阅读说明：本技术 无线谐振电路和可变电感血管监测植入物及其锚定结构 (Wireless resonance circuit, variable inductance blood vessel monitoring implant and anchoring structure thereof ) 是由 肖恩·昆兰 F·M·斯威尼 S·谢里丹 F·韦特林 于 2019-05-30 设计创作，主要内容包括：公开了无线的基于可变电感和谐振电路的血管监测设备、系统、方法和技术,包括为其专门配置的锚定结构,该无线的基于可变电感和谐振电路的血管监测设备、系统、方法和技术可用于协助医疗保健专业人员预测、预防和诊断各种心脏相关的健康状况和其他健康状况。(Wireless variable inductance and resonant circuit-based vascular monitoring devices, systems, methods, and techniques are disclosed, including anchoring structures specifically configured therefor, that may be used to assist healthcare professionals in predicting, preventing, and diagnosing various heart-related and other health conditions.)

1. An anchoring system for a vascular implant, the anchoring system comprising:

a plurality of implant attachment sections configured to attach to the vascular implant at spaced apart locations on the vascular implant, the attachment sections defining spaces between structures of the attachment sections for adhesive to enter and attach to the vascular implant; and

at least one anchoring section connected to each of the attachment sections, wherein at least one tissue engaging anchoring barb is disposed in each of the anchoring sections.

2. The anchoring system of claim 1, further comprising an anchoring isolation section disposed between the attachment section and at least one anchoring section, the anchoring isolation section configured to allow independent movement between the anchoring section and attachment section.

3. An anchoring system according to claim 1 or claim 2, comprising a plurality of individual anchoring elements, each having one said attachment section connected to one said anchoring section.

4. An anchoring system according to claim 3, wherein each of the individual anchoring elements is formed from a flat sheet or tube material and the at least one tissue engaging anchoring barb is cut from the surface of the material and bent outwardly.

5. An anchoring system according to claim 1 or claim 2, further comprising a plurality of anchoring sections coupled by crown sections to form an anchoring frame having a resilient concentric zig-zag structure.

6. An anchoring system according to claim 5, wherein crown segments provided at opposite ends of the anchoring section define first and second ends of the anchoring frame, and at least one attachment section is connected to each crown segment at least one end of the anchoring frame.

7. An anchoring system according to claim 5 or claim 6, wherein the frame is discontinuous with one of the crown sections forming a slotted crown having two crown section pieces spaced apart by a gap and an attachment section connected to each crown section piece.

8. An anchor for a vascular implant comprising a tubular member that is cut and formed in segments, the anchor comprising:

an anchoring section comprising at least one outwardly extending tissue engaging barb formed in the anchoring section by cutting and bending a portion of the anchoring section outwardly; and

an attachment section connected to the anchoring section, the attachment section configured to attach to the vascular implant, the attachment section defining a space between structures of the attachment section for adhesive to enter and attach to the vascular implant.

9. The anchor of claim 8, further comprising an isolation section disposed between the anchoring section and the attachment section, the isolation section configured to allow independent movement between the anchoring section and attachment section.

10. An anchoring frame for a vascular implant, comprising an elastic concentric zigzag structure formed by a plurality of support sections coupled to each other by circular crown sections, wherein:

the structure having two ends, wherein the crown section is disposed at one of the two ends and the support section is between the two ends;

at least a plurality of the support sections form an anchoring section having at least one tissue engaging barb;

at least one attachment section is connected to each crown section on at least one of the ends of the structure; and

each attachment section includes an elongated member defining a space between structures of the attachment section for adhesive to enter and attach to the vascular implant.

11. The anchoring frame of claim 10, further comprising an anchoring spacer segment disposed between each attachment segment and each of the crown segments, the anchoring spacer segment configured to allow independent movement between the anchoring segments and attachment segments.

12. An anchoring frame according to claim 10 or claim 11, wherein the frame is electrically discontinuous with a non-conductive gap formed in the zig-zag formation.

13. The anchoring frame of claim 12 wherein the non-conductive gap comprises one of the crown segments forming a slotted crown having two crown segment pieces separated by a gap and an attachment segment connected to each crown segment piece.

14. The anchoring frame of any one of claims 10-13 wherein each tissue engaging barb is disposed on the support section at an angle relative to the support section such that when the anchoring frame is deployed within a blood vessel lumen in contact with a lumen wall, the barb is positioned substantially parallel to a direction of blood flow in the blood vessel lumen.

15. The anchoring frame of any one of claims 10-14, wherein when deployed in a vessel lumen, the anchoring frame expands to contact the lumen wall, and the support sections are straight to allow apposition of each full support section and each crown section against the vessel lumen wall for multiple vessel lumen diameters with a single size anchoring frame.

16. An anchoring system according to any one of claims 1-7, an anchor according to any one of claims 8-9 or an anchoring frame according to any one of claims 10-15, wherein the attachment sections comprise alternating ridge and groove like structures when a groove like region provides space for adhesive to attach to the implant between ridge like structures.

17. The anchoring system of any one of claims 1-7, the anchor of any one of claims 8-9, or the anchoring frame of any one of claims 10-15, wherein the attachment section comprises a series of holes formed along the attachment section.

18. An anchoring system according to any one of claims 1-7, an anchor according to any one of claims 8-9 or an anchoring frame according to any one of claims 10-15, wherein the attachment section comprises a helical member having an inner diameter configured to be received on an outer diameter of an implant structure.

19. An anchoring system, anchor or frame according to claim 18, wherein the helical member is configured to engage the implant in an interference fit.

20. An anchoring system, anchor or frame according to any preceding claim, wherein the attachment section comprises a breakable connection to allow separation of the anchoring section from the implant.

21. An anchoring system, anchor or frame according to claim 20, wherein the breakable connection is configured to self-detach after a predetermined period of time.

22. An anchoring system, anchor or frame according to claim 20, wherein the breakable connection is configured to separate in response to externally directed energy.

23. An anchoring system, anchor or anchoring frame as defined in any preceding claim, further comprising a recapture feature disposed opposite the attachment section, the recapture feature configured to releasably engage a corresponding feature on a distal end of a deployment device.

24. The anchor of claim 23 wherein the recapture feature comprises a portion of the anchor segment opposite the attachment segment configured with a protrusion or opening.

25. The anchoring frame of claim 23, wherein the recapture feature comprises a recapture element extending from a crown section of the anchoring frame opposite the attachment section, the recapture element having a notch or opening engageable with a distal end of the deployment device.

26. A vascular implant adapted to be deployed and implanted in a patient's vasculature and positioned at a location in a vascular lumen in contact with a lumen wall, the implant comprising an anchoring system, plurality of anchors or anchoring frame according to any one of the preceding claims attached to a vascular device, wherein each attachment section is attached to a separate section of the vascular device.

27. The vascular implant of claim 26, further comprising a backflow material that melts into a space defined by the attachment section to secure the attachment section to the vascular device.

28. The vascular implant of claim 26 or claim 27, wherein:

the vascular device includes an elastic sensor construct configured to expand and contract in size with natural movement of the lumen wall;

the electrical characteristic of the elastic sensor configuration varies in a known relationship to the dimensional expansion and contraction of the elastic sensor configuration; and

the elastic sensor configuration generates a wireless signal indicative of the electrical characteristic, which can be wirelessly read outside the vessel lumen to determine a size of the vessel lumen.

29. The vascular implant of claim 28, wherein the elastic sensor configuration comprises an elastic concentric zigzag structure formed of a plurality of straight support sections coupled to one another by circular crown sections, wherein the straight sections are configured to allow juxtaposition of each complete straight support section and each crown section against the vessel lumen wall for the plurality of vessel lumen diameters with a single size elastic sensor configuration.

30. The vascular implant of claim 28 or 29, wherein:

the elastic sensor construct is configured and dimensioned to engage the cavity wall and substantially permanently implant itself on or in the cavity wall;

the elastic sensor arrangement having a variable inductance associated with dimensional expansion and contraction of the elastic sensor arrangement in at least one dimension; and is

When the elastic sensor arrangement is excited by an energy source for the arrangement, the elastic sensor arrangement generates a signal that is wirelessly readable outside the patient body that is indicative of the value of the at least one dimension, so that the size of the vessel lumen can be determined.

31. The vascular implant of any of claims 28-30, wherein the elastic sensor configuration comprises a coil configured to engage at least two opposing points on the wall of the vascular lumen, the inductance of the coil varying based on the distance between the two opposing points on the coil corresponding to the distance between the points on the wall of the lumen.

32. The vascular implant of claim 31, wherein the coil is rotationally symmetric about a longitudinal axis.

33. The vascular implant of any of claims 28-32, wherein the elastic sensor configuration is configured to expand and contract with the lumen wall along substantially any transverse axis of the blood vessel, thereby varying the variable inductance.

34. The vascular implant of any of claims 28-33, wherein the spring sensor configuration includes a resonant circuit having a resonant frequency that varies with the variable inductance, the signal being related to the resonant frequency.

35. The vascular implant of any of claims 31-34, wherein:

the coil comprises a resonant circuit having an inductance and a capacitance defining a resonant frequency, wherein the resonant frequency varies based on a distance between the at least two points; and

the coil is configured to be excited from outside the patient's body by a magnetic field directed at the coil.

36. The vascular implant of any of claims 31-35, wherein the coil is formed of litz wire.

37. A wireless vascular monitoring system comprising the vascular implant of any of claims 28-36 and a patient-external antenna loop, the patient-external antenna loop comprising:

a base layer having a sufficient length to form a discontinuous circumferential ring completely around a patient;

at least one continuous loop of antenna wire disposed on the base layer, the continuous loop having a length sufficient to extend substantially around the patient when the base layer is positioned around the patient;

a connection for a communication link between at least one continuous loop of the antenna core and a control system.

38. The wireless vascular monitoring system of claim 37, wherein at least one continuous loop of the antenna core wire has a sufficient length such that loop ends are substantially adjacent when the substrate is wrapped around a patient.

39. A patient-external antenna loop for a wireless vascular monitoring system, the patient-external antenna loop comprising:

a base layer having a sufficient length to form a discontinuous circumferential ring completely around a patient;

at least one continuous loop of antenna core disposed on the base layer, the continuous loop having a length sufficient to extend substantially around a substantially adjacently positioned patient loop end when the base layer is positioned around the patient;

a connection for a communication link between at least one continuous loop of the antenna core wire and a control system.

40. An anchor for a wireless vascular monitoring implant, the anchor comprising:

an anchoring section configured to engage a vessel lumen wall within a vessel lumen in which the monitoring implant is placed, the anchoring section comprising at least one outwardly extending barb; and

an attachment section configured for attachment to an elastic portion of the sensor construction, the attachment portion comprising a helical member dimensioned to slide over a wire or coil portion of the monitoring implant in an interference fit therewith, the helical portion further defining a space between the helices sufficient to receive a binder therebetween.

41. The anchor of claim 40, further comprising an isolation section disposed between the anchoring section and the attachment section, the isolation section configured to at least partially mechanically isolate movement of the anchoring section relative to the attachment section.

42. The anchor of any one of claims 40-41 wherein the bonding agent comprises a polymeric reflow material.

43. The anchor of any one of claims 40-42 wherein the helical member has an inner diameter sized to create a positional interference fit with an outer diameter of a coil portion of the monitoring implant.

44. A method of manufacturing a wireless vascular implant, comprising:

providing a resilient frame construction configured to assume a desired shape for the implant in a free state;

winding a plurality of coil wires around the frame construction to form a coil on the frame construction;

forming connection terminals on opposite ends of the coil wire;

placing a plurality of anchors over the coil formed on the frame construction, the anchors having a helical section configured to be received over the coil in an interference fit therewith;

bonding the anchor to the coil with a bonding material flowing between spaces in the helical section; and

attaching opposing terminals of a capacitor to the opposing connection terminals.

45. The method of manufacturing a wireless vascular implant as in claim 44, wherein the bonding the anchor comprises placing a polymeric return tube over the helical section on the coil and melting the return tube.

46. An implant for positioning in a body lumen in engagement with a wall of the lumen, the implant comprising:

an implant body comprising at least one wire component having an outer diameter; and

an anchoring element comprising an attachment portion for attaching the anchoring element to the at least one wire component, wherein the attachment portion comprises a helical section defining an inner diameter sized to fit over an outer diameter of the wire component engaged with the helical section.

47. The implant of claim 46, wherein the helical section is sized to form an interference fit with an outer diameter of the at least one wire member.

48. The implant of claim 47, further comprising a bonding material flowing between open areas of the helical section.

49. The implant of claim 47 or 48, wherein the interference fit is a positional interference fit.

50. An anchoring frame for a vascular implant, the anchoring frame comprising:

a resilient concentric zig-zag structure formed of a plurality of support sections joined to one another at acute angles by circular crown sections;

at least one tissue engaging barb disposed in a plurality of said support sections;

means for attaching the zig-zag structure to a vascular implant; and

a non-conductive gap formed in the zigzag structure such that the anchoring frame is electrically discontinuous.

51. The anchoring frame of claim 50, wherein:

the resilient concentric zigzag structure has two ends, wherein the crown section is disposed at one of the two ends with the support section therebetween;

the means for attaching comprises at least one attachment section connected to a plurality of crown sections on at least one of the ends of the structure;

each attachment section includes an elongated member defining a space between structures of the attachment section for an adhesive to enter and attach to the vascular implant.

52. The anchoring frame of claim 50 or claim 51, wherein the means for attaching comprises anchoring spacers for allowing independent movement between the resilient concentric zig-zag structure and an implant attached thereto.

53. The anchoring frame of any one of claims 50-52, wherein the non-conductive gap comprises one of the crown segments forming a slotted crown having two crown segment pieces spaced apart by a gap and an attachment segment connected to each crown segment piece.

54. The anchoring frame of any one of claims 50-53, wherein when deployed in a vessel lumen, the anchoring frame expands to contact the lumen wall, and the support segments are straight to allow apposition of each full support segment and each coronal segment against the vessel lumen wall for multiple vessel lumen diameters with a single size anchoring frame.

55. An anchoring frame for a vascular implant, wherein the anchoring frame expands to contact a lumen wall when the anchoring frame is deployed in a vascular lumen, the anchoring frame comprising:

a resilient concentric zigzag structure formed of a plurality of straight support sections coupled to one another by circular crown sections;

at least one tissue engaging barb disposed in a plurality of said support sections; and

means for attaching the zig-zag structure to a vascular implant;

wherein the straight configuration of the support segments allows for juxtaposition of each complete support segment and each crown segment against the vessel lumen wall for multiple vessel lumen diameters under a single size anchoring framework.

56. The anchoring frame of claim 55, wherein:

the resilient concentric zigzag structure has two ends, wherein the crown section is disposed at one of the two ends and the support section is between the two ends;

the means for attaching comprises at least one attachment section connected to a plurality of crown sections on at least one of the ends of the structure; and

each attachment section includes an elongated member defining a space between structures of the attachment section for adhesive to enter and attach to the vascular implant.

57. A wireless vascular sensor configured to be implanted in a lumen of a blood vessel in contact with a lumen wall, the sensor comprising an elastic sensor construct configured to expand and contract in size with natural movement of the lumen wall, wherein:

the elastic sensor configuration comprises an elastic concentric zigzag structure formed of a plurality of straight support sections coupled to each other by circular crown sections, wherein the straight support sections are configured to allow juxtaposition of each complete straight support section and each crown section against the vessel lumen wall for a plurality of vessel lumen diameters with a single size elastic sensor configuration;

the electrical characteristic of the elastic sensor configuration varies in a known relationship to the dimensional expansion and contraction of the elastic sensor configuration; and is

The elastic sensor configuration generates a wireless signal indicative of the electrical characteristic, which can be wirelessly read outside the vessel lumen to determine a size of the vessel lumen.

58. The wireless vascular monitoring implant of claim 57, wherein:

the elastic sensor construct is configured and dimensioned to engage the cavity wall and substantially permanently implant itself on or in the cavity wall;

the elastic sensor arrangement having a variable inductance associated with dimensional expansion and contraction of the elastic sensor arrangement in at least one dimension; and is

When the elastic sensor arrangement is excited by an energy source for the arrangement, the elastic sensor arrangement generates a signal that is wirelessly readable outside the patient body that is indicative of the value of the at least one dimension, so that the size of the vessel lumen can be determined.

59. The wireless vascular monitoring implant of any of claims 57-58, wherein the elastic sensor configuration comprises a coil configured to engage at least two opposing points on the wall of the vascular lumen, an inductance of the coil varying based on a distance between the two opposing points on the coil corresponding to a distance between the points on the wall of the lumen.

60. The wireless vascular monitoring implant of any of claims 57-59, wherein the elastic sensor configuration is configured to expand and contract with the lumen wall along substantially any transverse axis of the blood vessel, thereby varying the variable inductance.

61. The wireless vascular monitoring implant of any of claims 57-60, wherein the spring sensor configuration includes a resonant circuit having a resonant frequency that varies with the variable inductance, the signal being related to the resonant frequency.

62. The wireless vascular monitoring implant of any of claims 59-61, wherein:

the coil comprises a resonant circuit having an inductance and a capacitance defining a resonant frequency, wherein the resonant frequency varies based on a distance between the at least two points; and

the coil is configured to be excited from outside the patient's body by a magnetic field directed at the coil.

FIELD OF THE DISCLOSURE

The present invention relates generally to the field of vascular monitoring. In particular, the present invention relates to wireless vascular monitoring implants and anchoring structures therefor. More specifically, embodiments disclosed herein relate to fluid volume sensing in the Inferior Vena Cava (IVC) using a wireless, remote, or automatically actuatable implant for monitoring or managing blood volume.

Background

Others have attempted to develop vascular monitoring devices and techniques, including those directed to monitoring vascular arterial or venous pressure or vessel lumen size. However, many such existing systems are catheter-based (not wireless) and therefore can only be used in a clinical setting for a limited period of time and can carry the risks associated with prolonged catheterization. For wireless solutions, the complexity of deployment, fixturing, and interrelationships between these factors and detection and communication, at best, leads to inconsistent results with these previously developed devices and techniques.

Existing wireless systems focus on pressure measurement, which is less responsive to the fluid state of the patient in IVC than IVC sizing. However, systems designed for measuring vessel dimensions also have a number of disadvantages in monitoring in IVC. Electrical impedance based systems require the electrodes to be placed specifically across the width of the vessel. This type of device presents particular difficulties when attempting to monitor IVC size due to the fact that IVCs do not expand and contract symmetrically as most other vessels that may need to be monitored. The accurate positioning of such positioning-related sensors is an issue that has not been adequately addressed. IVC monitoring presents additional challenges arising from IVC physiology. IVC walls are relatively compliant compared to other blood vessels, and therefore they can be more easily distorted by the forces exerted by the implant to maintain positioning of the implant within the blood vessel. Thus, devices that can function satisfactorily in other blood vessels may not be able to be accurately monitored in an IVC due to the distortion created by the force of the implant on the wall of the IVC. Therefore, new developments in this area are desirable in order to provide physicians and patients with reliable and affordable wireless vessel monitoring implementations, particularly in the key area of heart failure monitoring.

Summary of the disclosure

Embodiments disclosed herein include wireless vascular monitoring devices, circuits, methods, and related techniques for assisting healthcare professionals in predicting, preventing, and diagnosing various conditions, indicators of which may include vascular fluid status. Using the disclosed embodiments, metrics including, for example, relative fluid state, fluid responsiveness, fluid tolerance, or heart rate may be accurately estimated.

In one implementation, the present disclosure is directed to a wireless vascular monitoring implant adapted to be deployed and implanted into a patient's vasculature and positioned at a monitoring location in a vessel lumen in contact with a lumen wall. The implant includes an elastic sensor configuration configured to expand and contract in size with natural movement of the cavity wall; wherein the electrical properties of the elastic sensor configuration change in a known relationship to its dimensional expansion and contraction; and the elastic sensor is configured to generate a wireless signal indicative of the electrical characteristic, the signal being wirelessly readable outside the vessel lumen to determine a dimension of the vessel lumen; the resilient sensor construct is configured and dimensioned to engage the cavity wall and substantially permanently implant the resilient sensor construct itself on or in the cavity wall; the elastic sensor configuration has a variable inductance associated with its dimensional expansion and contraction in at least one dimension; and the elastic sensor configuration, when powered by the energy source for the configuration, generates a signal wirelessly readable outside the patient's body indicative of a value of at least one dimension, whereby the size of the vessel lumen can be determined; wherein the elastic sensor configuration comprises a coil configured to engage with at least two opposing points on the vessel lumen wall, the coil having an inductance that varies based on a distance between the two opposing points on the coil, the distance between the two opposing points on the coil corresponding to a distance between the points on the lumen wall; wherein the coil is rotationally symmetric about the longitudinal axis; wherein the elastic sensor configuration is configured to expand and contract with the lumen wall along substantially any transverse axis of the blood vessel to cause the variable inductance to change; wherein the elastic sensor construct further comprises a frame having at least one elastic portion formed with at least two points configured to be positioned relative to each other so as to engage opposing surfaces of the lumen wall when the sensor construct is positioned in the monitoring position in contact with the lumen wall, wherein the coil is formed on the frame by at least one wire arranged around the frame so as to form a plurality of adjacent strands around the frame; wherein the resilient sensor arrangement comprises a resonant circuit having a resonant frequency which varies with variable inductance, the signal being related to the resonant frequency; wherein the coil comprises a resonant circuit having an inductance and a capacitance defining a resonant frequency, wherein the resonant frequency varies based on a distance between at least two points; and the coil is configured to be excited by a magnetic field directed to the coil from outside the patient's body.

These and other aspects and features of the non-limiting embodiments of the present disclosure will be apparent to those skilled in the art from the following description of specific non-limiting embodiments of the invention, which is to be read in connection with the accompanying drawings.

Brief Description of Drawings

For the purpose of illustrating the disclosure, the drawings show aspects of one or more embodiments of the disclosure. It should be understood, however, that the present disclosure is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 schematically depicts an embodiment of a wireless resonant circuit-based vascular monitoring ("RC-WVM") system of the present disclosure;

FIG. 1A schematically depicts a portion of an alternative embodiment of an RC-WVM system of the present disclosure;

fig. 2 and 2A illustrate an alternative embodiment of an RC-WVM implant made in accordance with the teachings of the present disclosure;

fig. 2B is a schematic detailed view of the capacitor segment of the RC-WVM implant illustrated in fig. 2;

fig. 3, 3A, 3B, 3C and 3D illustrate embodiments of strip antennas as schematically depicted in the system of fig. 1;

fig. 3E schematically depicts the orientation of the antenna strap relative to the implanted RC-WVM implant and the magnetic field generated thereby;

FIG. 4 is a block diagram illustrating an embodiment of system electronics;

fig. 5A and 5B illustrate fixed frequency RF burst excitation signal waveforms;

FIGS. 6A and 6B illustrate swept RF burst excitation signal waveforms;

fig. 7A and 7B illustrate multi-frequency RF burst excitation signal waveforms;

FIG. 8 illustrates waveform pulse shaping;

fig. 9 schematically illustrates aspects of an embodiment of a delivery system for an RC-WVM implant as disclosed herein;

fig. 9A schematically illustrates a distal end of an alternative embodiment of a delivery system for an alternative RC-WVM implant with an attached anchoring frame as disclosed herein;

fig. 10A, 10B, 10C, 10D and 10E illustrate signals obtained in preclinical experiments conducted using a prototype system and the RC-WVM implant shown in fig. 1 and 2;

11A, 11B and 11C illustrate another alternative RC-WVM implant embodiment in accordance with the teachings of the present disclosure;

FIG. 12 illustrates assembly of an alternative RC-WVM implant embodiment, such as that shown in FIGS. 11A-C;

FIG. 13 is a detailed view of the anchoring structure mounted on the implant prior to encapsulation;

14A, 14B and 14C illustrate alternative anchoring structures for use with the RC-WVM implant embodiment;

fig. 15A and 15B illustrate an alternative embodiment of a strip antenna for use with the RC-WVM implant and system as described herein;

fig. 16A and 16B illustrate a recapture feature that facilitates positioning and repositioning of the RC-WVM implant during placement using a delivery catheter disclosed herein;

FIG. 17 is a perspective view of an alternative RC-WVM implant embodiment with attached anchor frames and axial anchor barbs;

FIG. 18 is a perspective view of an anchor frame such as shown in FIG. 17;

FIG. 19 is a detail view showing the attachment of the anchor frame to the support section of the RC-WVM implant;

fig. 20 is a detail view showing a gap in the anchoring frame that prevents the magnetic field from coupling with the anchoring frame;

fig. 21 illustrates another alternative embodiment in which anchoring frames are provided on both ends of the RC-WVM implant;

fig. 22A, 22B and 22C illustrate another embodiment of the anchoring frame in which the anchoring barbs are oriented parallel to the anchoring frame posts.

23A, 23B, and 23C illustrate another embodiment of an anchoring frame with anchoring barbs oriented in the direction of flow in a blood vessel in which the RC-WVM is implanted;

fig. 24A and 24B illustrate yet another embodiment of an anchoring frame in which the anchoring barbs are positioned at the top of the anchoring frame;

fig. 25A illustrates a shaped anchor frame with adjacent anchor barbs on the same side of the frame posts; and figure 25B shows an alternative with dual anchors at each anchor location;

fig. 26A, 26B, 26C, 26D, 26E, 26F, 26G, and 26H each illustrate an alternative embodiment of an anchoring barb;

FIG. 27 is a schematic cross-sectional view showing the non-conductive connections of two anchoring frame members;

FIG. 28 shows a perspective view of another alternative anchoring frame embodiment; and

fig. 29A, 29B, 29C, and 29D each illustrate different alternative embodiments of anchoring frame attachment arms.

Detailed Description

Aspects of the present disclosure relate to wireless resonant circuit-based vascular monitoring ("RC-WVM") implants, systems, methods, and software, including an excitation feedback monitoring ("EFM") circuit that may be used to excite an RC-WVM implant with an excitation signal and receive a characteristic feedback signal generated by the RC-WVM implant. By automatically or manually analyzing feedback generated by the RC-WVM implant, healthcare professionals can be helped to predict, prevent, and diagnose various heart-related, kidney-related, or vessel-related health conditions. For example, feedback generated by the RC-WVM implant at a particular time may be compared to feedback generated by the RC-WVM implant at other times and/or feedback generated by a reference RC-WVM implant to understand vessel geometry and thereby estimate relative fluid status, fluid responsiveness, fluid tolerance, heart rate, respiration rate, and/or other metrics. One or more of these estimates may be automatically or manually generated to monitor the patient's state and provide feedback to the healthcare professional and/or patient in the event of any abnormalities or related trends.

Overview of the System

The unique physiology of IVC presents several unique challenges in attempting to detect and account for changes in the size of the IVC due to changes in the fluid status of the patient. For example, IVC walls in a typical monitoring region (i.e. between the hepatic and renal veins) are relatively compliant compared to other blood vessels, meaning that changes in vessel volume may cause changes in the relative distance between the anterior and posterior walls to be different compared to the medial and lateral walls. Thus, it is typical that a change in fluid volume will cause a conflicting change in the geometry and movement of the blood vessel; that is, as blood volume decreases, IVC tends to become smaller and collapse with breathing, while as blood volume increases, IVC tends to become larger and collapse with breathing decreases. The systems and implants disclosed herein are uniquely configured to compensate for and account for such conflicting changes.

As shown in fig. 1, a system 10 according to the present disclosure may generally include an RC-WVM implant 12 configured for placement in an IVC of a patient, a control system 14, an antenna module 16, and one or more remote systems 18, such as a processing system, a user interface/display, data storage, etc., in communication with the control and communication module via one or more data links 26, which may be wired or remote/wireless data links. In many embodiments, the remote system 18 may include a computing device and a user interface that serves as an external interface device, such as a laptop, tablet, or smartphone.

The RC-WVM implant 12 generally includes a variable inductance, constant capacitance, resonant L-C circuit formed as a resiliently collapsible coil structure that moves with the IVC wall as the IVC wall expands and contracts due to changes in fluid volume when positioned at a monitoring location within the patient IVC. The variable inductance is provided by the coil structure of the implant such that the inductance varies as the size of the coil varies as the IVC wall moves. The capacitive elements of the circuit may be provided by discrete capacitors or by specifically designed intrinsic capacitances of the implant structure itself. Embodiments of the RC-WVM implant 12 may also be provided with anchoring and isolation devices that are inherently designed into the implant structure, or with unique additional such structures, to ensure that the implant is securely and properly positioned in the IVC without unduly distorting the vessel wall, thereby distorting or otherwise negatively affecting the measurements determined by the implant. Typically, the RC-WVM implant 12 is configured to at least substantially permanently implant itself in the wall of a lumen in which it is placed upon deployment, and does not require physical connection (for communication, power, or other means) to a device outside the patient's body after implantation. As used herein, "substantially permanently implanted" means that in normal use, the implant will remain implanted in the vascular lumen wall throughout its useful life, and may integrate to varying degrees into the vascular lumen wall due to tissue ingrowth, but may be intentionally removed by an endovascular intervention or surgical removal procedure specifically performed to remove the implant as medically indicated. Details of alternative embodiments of implant 12 (as shown in fig. 2, 2A, and 11A-C) are provided below. In particular, it should be noted that any of the alternative RC-WVM implants described herein may be used in the alternative system 10 described herein without further modification of the system unless a modification can be determined.

Control system 14 includes, for example, functional modules for signal generation, signal processing, and power supply (generally including EFM circuitry and indicated as module 20) and a communication module 22, communication module 22 facilitating communication with and data transmission to various remote systems 18 over a data link 26 and optionally over other local or cloud-based networks 28. Details of exemplary embodiments of control system 14, modules 20 and 22, and elements in place of the EFM circuitry are described below and illustrated in FIG. 4. After being excited by the transmit coil of the EFM circuitry, the results may be communicated to the patient, caregiver, medical professional, health insurance company, and/or any other desired and authorized party via the remote system 18, either manually or automatically, in any suitable manner (e.g., orally, by printing out a report, by sending a text message or email, or otherwise) after analyzing the signals received from the RC-WVM implant 12.

The antenna module 16 is connected to the control system 14 by a power supply and communication link 24, and the communication link 24 may be a wired or wireless connection. Based on the signals provided by the EFM circuitry of the control system 14, the antenna module 16 generates a properly shaped and oriented magnetic field around the RC-WVM implant 12. The magnetic field excites the LC circuit of the RC-WVM implant 12, causing it to generate a "ring-back" signal indicative of the then current inductance value. Because the inductance value depends on the geometry of the implant, which, as described above, varies based on the size of the IVC in response to changes in fluid state heart rate, etc., the ringback signal may be interpreted by the control system 14 to provide information about the geometry of the IVC and the associated fluid state. Thus, the antenna module 16 also provides a receiving function/antenna as well as a transmitting function/antenna. In some embodiments, the transmit and receive functions are performed by a single antenna, and in other embodiments, each function is performed by a separate antenna. The antenna module 16 is schematically depicted in fig. 1 as an antenna strap, this embodiment being described in more detail below and shown in fig. 3A-D.

Fig. 1A illustrates an alternative embodiment of the antenna module 16 as an antenna board 16a, in which the transmit coil 32 and the receive coil 34 are disposed in a board or mattress 36, and the patient has his/her back lying on the board or mattress 36, with the RC-WVM implant 12 (implanted in the IVC) positioned above the coils 32, 34. The antenna module 16 as shown in fig. 1A is functionally equivalent to other alternative antenna modules disclosed herein; as described above, the antenna module 16 is connected to the control system 14 through the power supply and communication link 24. Another alternative embodiment of a strip antenna module is shown in fig. 115A and 15B. The planar antenna module may also be configured in a wearable configuration, for example, where the antenna coil is integrated into a wearable garment, such as into a backpack or vest. The antenna module 16 may also include a coil adapted to be secured directly to the patient's skin, for example over the abdomen or back, by tape, glue, or other means, or the coil may be adapted to be integrated into furniture, such as a chair back. As will be understood by those skilled in the art, the various embodiments of the antenna module 16 as described herein may be used with the system 10 as shown in fig. 1 without additional changes to the system or the antenna module, except as expressly noted herein.

The variable inductance L-C circuit produces a resonant frequency that varies with the change in inductance. With the implant securely fixed at a known monitoring location in the IVC, changes in the geometry or dimensions of the IVC cause changes in the configuration of the variable inductor, which in turn causes changes in the resonant frequency of the circuit. These changes in resonant frequency can be correlated to changes in vessel geometry or size by the RC-WVM control and communication system. Thus, not only should the implant be securely positioned at the monitoring location, but at least the variable coil/inductor portion of the implant should also have a predetermined elasticity and geometry. Thus, in general, variable inductors are specifically configured to change shape and inductance in proportion to changes in vessel geometry. In some embodiments, the anchoring and isolation device will include a shape and compliance in the sensor coil structure of the implant that is suitably selected and configured to move with the vessel wall while remaining positioned. Such embodiments may or may not include additional anchoring features as discussed in more detail below. Alternatively, the anchoring and isolation means may comprise a separate structure spaced apart and/or mechanically isolated from the variable inductor coil structure, such that the anchoring function is physically and/or functionally separated from the measurement/monitoring function, such that any distortion or constraint on the blood vessel caused by the anchor is sufficiently far away from and/or isolated from the variable inductor so as not to unduly affect the measurement.

The RC-WVM implant 12, which is a variable inductor, is configured to be remotely energized by an electric field delivered by one or more transmit coils positioned within an antenna module external to the patient. When energized, the L-C circuit generates a resonant frequency that is then detected by one or more receive coils of the antenna module. Because the resonant frequency depends on the inductance of the variable inductor, changes in the geometry or size of the inductor caused by changes in the geometry or size of the vessel wall cause changes in the resonant frequency. The detected resonant frequency is then analyzed by the RC-WVM control and communication system to determine changes in vessel geometry or size. Information derived from the detected resonant frequency is processed by various signal processing techniques described herein and may be transmitted to various remote devices (such as a healthcare provider system or patient system) to provide status or, where appropriate, alarm or treatment modification. To facilitate the measurement of the detected resonant frequency, it is desirable to provide a design with a relatively high Q factor, i.e., a resonant circuit configuration: the signal/energy is maintained for a relatively long period of time, particularly when operating at lower frequencies. For example, to achieve the advantages of the design using litz wire as further described herein, it is desirable to operate in a resonant frequency range below 5MHz, typically between about 1MHz and 3MHz, in which case it is desirable for the Q factor of the resonant circuit configuration to be at least about 50 or greater.

Examples of complete System embodiments

Details of one possible embodiment of the complete exemplary system 10 are discussed below with reference to fig. 2-8. Hereinafter, details of other alternative embodiments of the system components are described. However, it should be understood that the exemplary system is not limited to use with the particular elements or components illustrated in fig. 1-8, and that any of the alternative components described subsequently may be substituted without variation of the overall system, unless otherwise indicated.

Fig. 2 illustrates one example of an RC-WVM implant 12 according to the present disclosure that may be used in the example system 10. The enlarged detail in the box of fig. 2 represents a cross-sectional view taken as shown. (Note that in cross-sectional views, the respective ends of the very thin lines may not be clearly visible due to their very small size). In general, the RC-WVM implant 12 comprises a resilient sensor configuration that generally includes an induction coil formed around an open center that allows blood to flow therethrough substantially unimpeded, wherein the induction coil changes inductance as the geometry of the configuration changes due to forces applied thereto. In this example, the implant 12a is formed as a resilient concentric zig-zag or chained "Z-shaped" structure having a series of support sections 38, the series of support sections 38 being joined at their ends by rounded crown sections (rounded crown sections)40 that form acute angles. The resulting structure may also be considered sinusoidal in appearance. This structure may be formed by winding the wire 42 onto a frame or core 44. In this alternative, the RC-WVM implant 12a has a shaped 0.010 "nitinol wire frame 44 around which 300 strands of 0.04mm diameter individual insulated gilliers wires 42 are wound in a single loop. In the case of a single loop winding, as can be seen in the cross-sectional view of fig. 2, the strands of wire 42 appear substantially parallel to the frame at any given point. The individual insulators on the litz wire 42 may be formed as a biocompatible polyurethane coating. Also in this particular example, the discrete capacitor 46 is provided with a capacitance of about 47 η F (nanofarad); however, the capacitance may be in the range of about 180 picofarads to about 10 picofarads to cover all possible allowable frequency bands (from about 148.5kHz to about 37.5MHz) for the RC-WVM implant 12.

In one alternative, rather than a relatively large number of strands being arranged in a single loop, a relatively small number of strands (e.g., in the range of about 10-20 strands, or more specifically about 15 strands) may be arranged in a relatively large number of loops (e.g., in the range of about 15-25 loops, or more specifically about 20 loops). In this alternative embodiment, the discrete capacitor element is replaced with an inherent coil capacitance formed based on the space between the parallel strands.

In another alternative embodiment, the implant 12a is configured to ensure that the support sections 38 are straight support sections between the crown sections 40. The straight support section may provide the following advantages: regardless of the size of the vessel in which the support section is deployed, the support section is in contact with the vessel wall throughout its length. When the sensor construction frame is formed, for example, by laser cutting the construction from a nitinol tube, the straight configuration of the straight support section may be achieved by shaping the support section to maintain the desired straight configuration.

Referring also to FIG. 2B, litz wire 42 is formed around a shaped nitinol frame 44. The ends of the litz wire 42, which may be covered with a layer of PET heat shrink tubing 60, are joined together with a capacitor 46 to form a loop circuit. The capacitor 46 comprises a capacitor terminal 52 connected to the litz wire 42 by a solder connection 54 with a gold wire contact 56. Gold wire contacts 56 are formed by removing (or burning off) the respective insulators from short sections at the ends of the litz wire 42 and joining the ends to form solid contacts, which can then be joined to the capacitor terminals 52 by solder connections 54. The capacitors, capacitor terminals and gold wire contacts are encapsulated in a suitable biocompatible insulating material 58, such as a reflowed polymer or epoxy. In an alternative embodiment, the entire structure may then be covered with a layer of PET heat shrink insulator 60. Alternatively, if it is determined that a short circuit should not be created through the frame, a gap may be provided in the frame at the capacitor or elsewhere.

As shown in fig. 2, the RC-WVM implant 12a is also optionally provided with an anchor 48 to help prevent migration of the implant after placement in the IVC. The anchors 48 may also be formed from a nitinol laser cut section or shaped wire and bonded to each support section 38. Barbs 50 extend outwardly at the ends of the anchors 48 to engage the IVC wall. In one embodiment, the anchor 48 is bi-directional in the cephalad and caudal directions; in other embodiments, the anchor may be in one direction, a mixture of two directions, or perpendicular to the blood vessel.

The overall structure of the RC-WVM implant 12 balances between electrical and mechanical requirements. For example, an ideal electrical sensor is as close to the solenoid as possible, with the strut length as short as possible and ideally zero, while mechanical considerations of deployment and stability dictate that the implant strut length is at least as long as the diameter of the vessel in which the strut is to be deployed, to avoid deployment in the wrong orientation and maintain stability. The dimensions of the elements of the RC-WVM implant 12a are identified by the letters A-F in FIG. 2, and examples of typical values for these dimensions suitable for a range of patient anatomies are provided below in Table I. In general, based on the teachings herein, those skilled in the art will recognize that the uncompressed, free-state (overall) diameter of the RC-WVM implant 12 should not significantly exceed the maximum expected fully-extended IVC diameter of a patient in which the RC-WVM implant will be used. The RC-WVM implant height should generally be selected to balance implant stability with geometry/flexibility/elasticity at the monitoring location, providing accommodation in the intended area of IVC without affecting the ability of the hepatic or renal veins of most humans, which may compromise the sensed data produced by the implant. Among other factors, height and stability considerations will be affected by the particular RC-WVM implant design configuration and whether or not significant anchoring features are included. Thus, as will be appreciated by those skilled in the art, a primary design consideration for the RC-WVM implant 12 according to the present disclosure is to provide the following structure: the structure forms a variable inductance L-C circuit capable of performing the measurement or monitoring functions described herein, and is configured to securely anchor the structure within the IVC without distorting the IVC wall by providing sufficient but relatively low radial force to the IVC wall.

Another alternative structure for the RC-WVM implant 12 is illustrated by the RC-WVM implant 12b as shown in fig. 2A. The enlarged detail in the box of fig. 2A again represents a cross-sectional view taken as indicated. In this embodiment, the overall structure of the implant 12b is similar to that of the implant 12a, formed on a frame having a straight support section 38 and a curved crown section 40. In this embodiment, the discrete capacitors in the previous embodiment are replaced by distributed capacitances between several strand wires. A plurality of strands (e.g., about fifteen strands) 64 are laid parallel to each other and twisted into a bundle. The bundle is then wrapped multiple times around the entire circumference of a wire frame 66 (which may be, for example, a 0.010 "diameter nitinol wire) to provide multiple parallel turns of the strand. The insulator between the bundles results in a distributed capacitance that causes the RC-WVM to resonate as before. Overall dimensions are similar and may be approximated as shown in table I. The outer insulating layer or coating 60 may be applied as previously described or using a dipping or spraying process. In this case, the L-C circuit is created without discrete capacitors by instead tuning the inherent capacitance of the structure through selection of the material and length/configuration of the strands. In this case, 20 turns of 15 strands are used in conjunction with the outer layer of silicone insulation 60 to achieve a capacitance in the range of about 40-50 η F inherent in the implant 12 b.

Unlike implant 12a, frame 66 of implant 12b is not continuous so as not to complete an electrical loop within the implant, as this would negatively impact performance. Any overlapping ends of the frame 66 are spaced apart with an insulating material, such as a heat shrink tube, an insulating epoxy, or a reflowed polymer. The RC-WVM implant 12b (which may or may not include an anchor). Alternatively, the implant is configured to be compliant/resilient to permit it to move with changes in the geometry or dimensions of the IVC wall while maintaining its positioning with minimal distortion of the natural movement of the IVC wall. This configuration can be achieved by appropriate selection of materials, surface features and dimensions. For example, the support section length of the frame must balance electrical performance with stability considerations, where shorter support section lengths may tend to improve electrical performance but longer support section lengths may increase stability.

To excite the RC-WVM implant 12 and receive back signals from the implant, the antenna module 16 will functionally include a transmit and receive antenna (or antennas). The antenna module 16 may thus be provided with physically distinct transmit and receive antennas, or as in the presently described exemplary system 10, provided by a single antenna that switches between a transmit mode and a receive mode. The antenna strip 16b shown in fig. 3 and 3A-D illustrates an example of an antenna module 16 that employs a single switched antenna. The single loop antenna is formed from a single wire and is placed around the abdomen of the patient. The wire antenna is directly connected to the control system 14.

In terms of mechanical construction, the antenna strap 16b generally includes a stretchable web section 72 and a buckle 74 with connections for the power and data links 24. In one embodiment, to accommodate the size of antenna strap 16b for patients having different girths (e.g., patients having girths ranging from about 700 and 1200 cm), a multi-layer construction made of a combination of high-stretch and low-stretch materials may be employed. In such embodiments, the base layer 76 is a combination of high stretch sections 76a and low stretch sections 76b, which are joined, such as by stitching. The outer layer 78, which has substantially the same contour as the base layer 76, may be constructed entirely of a high stretch material, which may be a 3D mesh fabric. Within each section, the antenna core 82 is provided in a serpentine configuration, with an overall length sufficient to accommodate the overall stretch of the section. The core wire 82 itself should not be stretched. Thus, the stretchability of the fabric layer is paired with the total core length to meet the desired girth adaptation for a particular belt design. The outer layer 78 is attached to the base layer 76 along the edges. Covering the stitching with adhesive material 80 is one suitable means for joining the two layers. The layers may be further bonded together by a hot melt bonding material placed between the layers. The end 81 of the mesh segment 72 is configured for attachment to the buckle 74.

The core 82 forming the antenna element is disposed between the layers and is provided in an extendable serpentine configuration so that it can expand and contract as the band is stretched. The intermediate section 84 of the core wire 82 corresponding to the low tension section 76b has a larger width. This section provides maximum sensitivity for reading signals from the RC-WVM implant 12, which is intended to be placed in the middle of the patient's back with the antenna strap 16b worn at the bottom of the chest at approximately the chest level. As one possible example, the core 82 may be made of 300 stranded 46AWG copper wire with a total length in the range of about 0.5-3 m. For an antenna strap configured to stretch to accommodate a patient girth in the range of about 700 to 1200mm, the total length of the core wire 82 may be approximately 2 m. In some embodiments, it is preferable to place the antenna strap closer to the caudal end, at a height approximately that of the elbow of the patient when standing.

Many ways of providing an operable buckle for such an antenna strap may be derived by those skilled in the art based on the teachings contained herein. Factors to be considered in designing such buckles include physical safety, ease of manipulation by a less agile person, and protection from electric shock caused by inadvertent contact with the electrical connector. By way of example, the buckle 74 includes two half buckles, an inner half 74a and an outer half 74 b. The buckle 74 provides not only a physical connection for the strap ends, but also an electrical connection for the antenna circuit formed by the core wire 82. With respect to the physical connection, the buckle 74 is relatively large in size to facilitate manipulation by a less dexterous person. A magnetic latch may be employed to assist closure, such as a magnetic pad 86a on the inner buckle half 74a connected to a magnetic pad 86b correspondingly disposed on the buckle outer half 74 b. If desired, the system may be configured to monitor the integrity of the belt circuit and thus detect a belt closure. After confirming the band is closed, the system may be configured to evaluate the signal strength received from the implant and make a determination as to whether the received signal is sufficient to be a complete reading. If the signal is insufficient, instructions may be provided to reposition the band to a more optimal position on the patient.

Electrical connection of the core wire 82 may be provided by recessed connector pins disposed on the opposing connector halves 88a and 88 b. The connection of the power and data links 24 may be provided, for example, via a coaxial RF cable, with a coaxial connector (e.g., an SMA plug) on the buckle 74 and the control system 14. As just one possible example, a suitable length of power and data link using a conventional 50 ohm coaxial cable is about 3 m.

As mentioned above, using a single coil antenna as in antenna strap 16b requires switching the antenna between transmit and receive modes. Such switching is performed within the control system 14, an example of which is schematically depicted as control system 14a in fig. 4. In this embodiment, the control system 14a includes functional modules 20, namely a signal generator module 20a and a receiver-amplifier module 20 b. These functional modules, along with a transmit/receive (T/R) switch 92, provide the required switching of the antenna strap 16b between transmit and receive modes.

Figure 3E schematically illustrates the magnetic field generated by antenna strap 16bInteraction with the RC-WVM implant 12. Both the antenna strap 16b and the implant 12 are disposed generally about the axis (a). For best results with strip antennas, the axes about which each is disposed will lie in substantially parallel orientations and, to the extent practicable, will be positioned coincidentally, as shown in fig. 3E. When properly oriented relative to each other, the current (I) in the core 82 of the antenna strap 16b generates a magnetic fieldThe magnetic fieldThe coil of the implant 12 is excited to cause it to resonate at a resonant frequency corresponding to its size/geometry at the time of excitation. The orientation between the antenna strap 16b and the implant 12 as shown in figure 3E minimizes the power necessary to excite the implant coil and produce a readable resonant frequency response signal.

As with any RF coil antenna system, the antenna and system must be matched and tuned for optimum performance. The values of the inductance, capacitance and resistance and their interrelationships should be carefully considered. For example, the coil inductance determines the tuning capacitance, while the coil resistance (including the tuning capacitance) determines the matching capacitance and inductance. In view of the relatively low power of the disclosed system, these aspects are particularly addressed to ensure that the RC-WVM implant 12 generates a sufficiently readable signal when actuated by a driving magnetic field. With an adjustable perimeter band, such as antenna band 16b (or with a different size antenna band), additional considerations are addressed due to the variable or different lengths of the antenna coils controlled by the control system. To address these considerations, separate tuning-matching circuits 94, 96 (fig. 4) are provided in the signal generator module 20a and the receiver-amplifier module 20b, respectively, as is understood in the art.

Using conventional coaxial cables for RF power transfer, as described above in one embodiment of the power and data link 24, optimal RF power transfer between the antenna and the control system is achieved when the system and antenna are impedance matched to a real resistance of 50 ohms. However, in the embodiments described above, the resistance of the antenna strap 16b is typically much lower than 50 ohms. A transformation circuit as part of the tune-match circuits 94, 96 may be used to transform the antenna resistance to 50 ohms. In the case of antenna strap 16b, a parallel capacitor transformation circuit has been found to be effective for this purpose. .

In one example of tuning using the aforementioned system components, a series capacitor is used that in combination with a matching capacitor forms the overall resonance. Using the measurements as set forth in table II below, the target resonant frequency was calculated to be 2.6MHz based on inductance and capacitance. Considering the inductance change in the case of stretching of the antenna strap 16b at 2.6MHz, for a length change of the perimeter of the antenna strap 16b between 1200mm and 700mm, the resonance frequency was correspondingly measured to change only from about 2.5MHz to about 2.6 MHz. Considering a resistance of 11.1 ohms, the Q factor of the cable/tape assembly is calculated to be 3. This low Q factor translates to a pulse full width at half maximum of 600kHz (a full width of the pulse at half f maximum of 600 kHz). This is much less than the change in resonant frequency due to stretching of the circumference of the band from 700mm to 1200 mm. Thus, the tuning value of antenna strap 16b is determined to be at 2.6MHz, C_Matching2.2nF and C_Tuning＝2.2nF。

While it is contemplated that variable length antennas such as those included in antenna strip 16b may face difficulties in tuning and maintaining the antenna as the length changes, it has been found that this is not the case when utilizing the present configuration. As noted above, by intentionally employing a cable for the power and data link 24 that has a relatively large inductance compared to the antenna inductance, the proportional change in inductance due to the change in diameter of the ribbon is not small enough to degrade performance.

Referring again to fig. 4, in addition to the tune-to-match circuit 94, the signal generator module 20a includes components that generate the signals required to fire the RC-WVM implant 12. These components include a Direct Digital Synthesizer (DDS)98, an anti-aliasing filter 100, a preamplifier 102, and an output amplifier 104. In one embodiment, the signal generator module 20a is configured to generate an RF burst excitation signal having a single, constant frequency tailored to the particular RC-WVM implant being paired with the system (exemplary waveforms are shown in fig. 5A and 5B). The RF bursts comprise a predetermined number of sinusoidal waveform pulses at a selected frequency with set intervals between bursts. The selected RF burst frequency value corresponds to the natural frequency of the paired RC-WVM implant 12 that will produce the lowest amplitude in the implant reader output. By doing so, an optimal excitation is achieved in the worst case of the implant response signal.

In an alternative implementation, the control system 14 excites the antenna module 16 at a predetermined frequency that is within the expected bandwidth of the paired RC-WVM implant 12. Next, the system detects the response from the paired RC-WVM implant and determines the implant natural frequency. The control system 14 then adjusts the excitation frequency to match the natural frequency of the paired implant and continues to excite at that frequency for the full reading cycle. As will be appreciated by the skilled person, the frequency determination and adjustment as described for this embodiment may be implemented via software using digital signal processing and analysis.

In another alternative implementation, each individual RF burst includes a continuous frequency sweep within a predetermined frequency range equal to the possible bandwidth of the implant (fig. 6A). This produces a broadband pulse that can excite the implant at all possible natural frequencies (fig. 6B). The excitation signal may continue in this "burst frequency sweep mode" or the control system may determine the natural frequency of the sensor and adjust to emit at only the natural frequency.

In a further alternative implementation, the excitation includes a short sweep of frequencies over a set of discrete frequency values covering the possible bandwidth of the paired RC-WVM implant 12. The frequency is sequentially incremented for each RF burst and the RMS value of the RC-WVM implant response is evaluated after each increment. The control system 14 then establishes the frequency that produces the maximum amplitude in the RC-WVM implant response and continues to fire the paired RC-WVM implant at that frequency until a predetermined amplitude drop is detected and the frequency sweep is restarted.

In yet another implementation, the excitation signal includes a set of predetermined frequencies, wherein each frequency remains constant. The control system 14 excites the antenna module 16 (and thus the mated implant) by applying equal amplitudes at all frequency components. The system detects the response from the paired implant and determines its natural frequency. Control system 14 then adjusts the relative amplitudes of the excitation frequency sets to maximize the amplitude of the excitation frequency that is closest to the natural frequency of the paired implant. The amplitudes of the other frequencies are optimized to maximize the response of the mated implant while meeting the requirements of electromagnetic radiation and transmission bandwidth limitations.

In another implementation, a Direct Digital Synthesizer (DDS)98 may be provided as a multi-channel DDS system to generate a simultaneous predetermined number of discrete frequencies that pertain to the estimated operating bandwidth of the paired RC-WVM implant 12 as shown in fig. 7A and 7B. The amplitude of each frequency component can be independently controlled to provide optimal excitation to a particular RC-WVM implant 12 based on the individual coil characteristics of that particular RC-WVM implant 12. In addition, the relative amplitude of each frequency component can be independently controlled to provide optimal excitation to the implant, i.e., the amplitudes of the frequency components are selected in a manner that maximizes the excitation signal in the worst case (i.e., most compression) for the paired implant to emit a response signal. In this arrangement, all outputs from the multi-channel DDS system 98 are added together based on a high speed operational amplifier using a summing amplifier 120.

In yet another implementation, the signal generator module 20a may be configured to provide pulse shaping as shown in fig. 8. Arbitrary waveform generation based on direct digital synthesis 98 is employed to produce pulses having a predetermined shape whose frequency spectrum is optimized to maximize the response of the mated RC-WVM implant 12. The amplitude of the frequency component that results in the looped-back signal decreasing in amplitude is maximized while the amplitude of the frequency component that results in the looped-back signal increasing in amplitude is decreased in order to obtain a substantially constant output signal amplitude and thus an improved response from the RC-WVM implant 12.

Referring again to fig. 4, in addition to the tune-matching circuit 96, the receiver module 20b includes components for implant response detection, data conversion and acquisition for signal analysis, such as a single-ended output differential output circuit (SE to DIFF)106, a Variable Gain Amplifier (VGA)108, a filter amplifier 110, and an output filter 112. During the receive period, the T/R switch 92 connects the antenna strap 16b to the receiver-amplifier 20b via the tuning and matching network 96. The response signal to be induced in the antenna strap 16b by the implant 12 is applied to a unity gain single-ended to differential amplifier 106. The conversion from single-ended to differential mode helps to cancel common mode noise from the implant response signal. Since the amplitude of the implant response signal is in the microvolt range, feeding the signal into the variable gain differential amplifier 108 after conversion from single ended to differential, the variable gain differential amplifier 108 is able to provide up to 80dB (10000 times) of voltage gain. The amplified signal is then applied to an active bandpass filter-amplifier 110 to eliminate out-of-band frequency components and provide an additional level of amplification. The resulting signal is applied to a passive high order low pass filter 112 for further cancellation of out-of-band high frequency components. The output of the filter is fed into a data conversion and communication module 22. The data conversion and communication module 22 includes components to provide data acquisition and transfer from the electronic system to an external processing unit. A high-speed analog-to-digital converter (ADC)114 converts the output signal of the receiver module 20b into a digital signal having a predetermined number of bits (e.g., 12 bits). The digital signal is transmitted to the microcontroller 116 in a parallel mode. In one implementation, a level shifter circuit is used to match the logic level of the ADC to the microcontroller. The data output by the ADC is stored in sequence in the microcontroller's internal flash memory. To maximize data throughput, Direct Memory Access (DMA) is used in this process. The microcontroller 116 is synchronized with the direct digital synthesizer 98 so data acquisition begins when an RF burst is transmitted for exciting the implant 12. Once triggered, the microcontroller captures a predetermined number of samples (e.g., 1024). The number of samples multiplied by the sampling period defines an observation window within which the response signal from the implant 12 is assessed. The observation window is matched to the length of the response signal from the implant 12, which depends on the time constant of the signal decay.

As a means of reducing noise, the response signal of the implant 12 is observed a predetermined number of times (e.g., 256 times), and then an average response is calculated. This approach greatly helps to increase the signal-to-noise ratio of the detected signal.

The average response is then transmitted to the external interface device 18 (e.g., a laptop computer) via the communication module 118. Different methods can be used for this. In one embodiment, the communication is performed using a UART interface from a microcontroller and external hardware is employed to convert from UART to USB. In the second embodiment, a microcontroller having USB driving capability is employed, and in this case, connection with an external interface device is realized by using only a USB cable. In yet another implementation, the communication between the microcontroller and the external interface device is wireless (e.g., via bluetooth).

The system is powered by a low voltage Power Supply Unit (PSU) consisting of an AC-DC converter with insulation between mains input and output providing a minimum of 2 patient protection Means (MOPP) according to IEC60601-1:2005+ AMD1:2012 clause 8. In this manner, the power supply provides shock protection to the user. The PSU can accommodate a wide range of mains voltages (e.g. from 90 to 264VAC) and mains frequencies (e.g. 47 to 63Hz) to allow operating the system in different countries with different mains specifications.

The control system 14a as described above utilizes software-based frequency detection. Thus, once the excitation frequency is optimized in terms of signal emission, the system 10 employing the control system 14a with the signal generator module 20a operates in an open loop mode, i.e., one or more of the frequency and amplitude of the emitted signal is not affected by the RC-WVM implant 12 response. On the receive side, using the amplifier-receiver module 20b, the control system 14a detects the response signal from the RC-WVM implant 12 and digitizes the signal using a high speed data converter. The raw digitized data is then transferred to a processing unit (e.g., a laptop computer or other device microcontroller) and a digital signal analysis technique (e.g., fast fourier transform) is applied to establish the frequency content of the signal. Thus, one advantage of using these software-based techniques is that no phase-locked loop (PLL) circuitry or the like is used or required in the control system 14 a.

Yet another component of the overall RC-WVM system as described herein is an RC-WVM implant delivery system. Fig. 9A and 9A schematically illustrate aspects of an intravascular delivery system for placing the RC-WVM implant 12 at a desired monitoring location within an IVC, which may generally include a delivery catheter 122, the delivery catheter 122 including an outer sheath 124 and a pusher 126 configured to be received in a lumen of the outer sheath 124. Generally, the insertion of devices into the circulatory system of a human or other animal is well known in the art and therefore not described in detail herein. One skilled in the art, after reading this disclosure in its entirety, will appreciate that the RC-WVM implant 12 may be delivered to a desired location in the circulatory system using, for example, a loading tool to load a sterile RC-WVM implant into a sterile delivery system that may be used to deliver the RC-WVM implant to the IVC via the femoral vein or other peripheral vascular access point, although other methods may also be used. Generally, the RC-WVM implant 12 will be implanted using a delivery catheter, the delivery catheter 122 being an illustrative example of the delivery catheter, and the RC-WVM implant 12 will be optimized for delivery via as small a catheter as possible. To facilitate this operation, the bend of implant crown section 40 (or ear as described later, collectively referred to as the "sensor construct end") may be a smaller radius bend to promote a low profile when inserted into a delivery catheter as shown. In one alternative, the pusher 126 may be provided with a stepped distal end (stepped distal end)128 having a reduced diameter end portion 130, the reduced diameter end portion 130 being configured to engage an inner periphery of the RC-WVM implant 12 when the RC-WVM implant 12 is compressed for delivery. For implant embodiments employing an anchor (e.g., anchor 48 in fig. 2 or anchor 48s in fig. 11A, etc.), end portion 130 may be configured to engage an inner perimeter defined by the anchor in a compressed configuration, as shown in fig. 9B. Alternatively, the pusher distal end 128 may be provided with a straight flat end or other end shape configured to cooperate with the particular RC-WVM implant and anchor design. For example, as shown in fig. 9A, an RC-WVM implant 12t having an anchoring frame 150 (see, e.g., fig. 17 and 18) may be deployed with a flat distal pusher 128 abutting the crown section 40 of the implant 12t, with the anchoring frame 150 disposed opposite the pusher 128.

In one deployment option, an RC-WVM implant may be inserted into the IVC from a peripheral vein (such as the femoral or iliac vein) to be positioned at a monitoring location between the hepatic and renal veins. It will be appreciated that the implant may also be introduced from other venous locations. Depending on the implant configuration, a particular orientation of the RC-WVM implant 12 may be required to optimize communication with the band reader antenna coil when placed in the IVC for fluid condition monitoring. To facilitate the desired placement or positioning, the length and diameter of the RC-WVM implant 12 may be designed such that it gradually expands ("flowers") when held in place with the pusher 126 and the sheath 124 is withdrawn. This gradual partial deployment helps ensure that the RC-WVM implant 12 is properly positioned in the IVC. The ratio of the sensor length to the vessel diameter (where the length is always larger than the vessel diameter) is also an important design factor to ensure that the sensor is deployed in the correct orientation in IVC. In another alternative, the distal end 128 of the pusher 126 may be configured to releasably retain the anchor or proximally oriented portion of the implant prior to full deployment of the implant from the outer sheath 124 so that the implant may be retracted for repositioning if desired. For example, small radially extending studs (studs) may be provided near the ends of the end portion 130, the end portion 130 engaging behind the proximal crown of the implant 12 as long as the implant 12 is compressed within the outer sheath 124, whereby the implant may be pulled back from the partially deployed position, but self-releases from the studs upon full deployment by expansion after confirmation of positioning. Conventional radiopaque markers may be provided at or near the distal end of the outer sheath 124 and/or pusher 126, as well as on the RC-WVM implant 12, to facilitate visualization during positioning and deployment of the implant. Typically, where an anchoring feature is employed, the implant will be positioned with the anchoring feature having a proximal orientation, so the anchor is the last to be deployed portion to facilitate proper orientation within the IVC and possibly allow for pull back and repositioning as may be required. Once the implant is fully deployed, the delivery catheter 122 may be withdrawn from the patient, leaving the implant 12 in the blood vessel as a discrete, self-contained unit without attached wires, leads, or other structures extending away from the monitoring location.

Example 1

The system as described herein has been evaluated in preclinical testing (pre-clinical testing) using an RC-WVM implant 12a (as in fig. 2), an antenna strip similar to antenna strip 16b (as in fig. 3), and a control system 14a (as in fig. 4). The implant is deployed into the ovine IVC using a delivery system 122 (as in fig. 9) using standard interventional techniques. Deployment is confirmed angiographically using intravascular ultrasound and using antenna straps.

Fig. 10A, 10B and 10C show the raw ring down signal (raw ring down signal), the detection of the maximum frequency and the conversion of the maximum frequency to the IVC area using the reference characteristic curve, respectively. Fig. 10A shows the original ring down signal in the time domain, where the resonant response of the RC-WVM implant decays over time. Modulation of the implant geometry results in a change in the resonant frequency, which can be seen as a difference between two different plotted traces. Fig. 10B shows the RC-WVM implant signal converted into the frequency domain and plotted over time. The maximum frequency in fig. 10A is determined (e.g., using a fast fourier transform) and plotted over time. A larger, slower modulation of the signal (i.e., three wide spikes) indicates respiratory-induced motion of the IVC wall, while a faster, smaller modulation superimposed on the signal indicates motion of the IVC wall in response to the cardiac cycle. Fig. 10C shows the frequency modulation plotted in fig. 10A converted to an IVC area versus time graph. (in this case, the conversion is based on a characteristic curve determined by bench testing of a series of sample diameter lumens following a standard laboratory/test procedure.) fig. 10C thus shows the change in IVC area at the monitoring location in response to the respiratory and cardiac cycles.

The ability of the RC-WVM implant 12 (in this case, the implant 12a) to detect IVC area changes due to fluid loading is illustrated in fig. 10D and 10E. In one example, the result of which is shown in fig. 10D, a 100ml fluid dose is added to the animal at 10ml/s after placement of the RC-WVM implant 12 in the ovine IVC and confirmation of implant signal receipt. The grey bands in fig. 10D indicate the application of fluid doses. As reflected by the reduced frequency loopback signal (ring-back signal) from the RC-WVM implant 12, the added flow capacity causes the IVC and the implant to expand therewith, which in turn causes the inductance of the implant to change, thus changing the frequency of its loopback response to excitation. In another example, the results are shown in fig. 10E, tilting the console to divert fluid within the animal. Starting from the left side in fig. 10E, the first gray band indicates the time of the initial tilt table. The tilting of the table causes the fluid to be displaced away from the IVC, causing the IVC diameter to decrease, and thus increasing the frequency of the loopback signal of the RC-WVM implant 12 as the RC-WVM implant 12 moves to a smaller diameter IVC. The second gray band indicates the time to return the table from tilting to flat. At this point, the fluid is transferred back into the IVC, causing the IVC to increase in size due to the increased fluid capacity and thus reducing the frequency of the looped-back signal as explained above.

These output signals therefore demonstrate the detection of the modulation of IVC with breathing. In particular, it is to be understood that embodiments of the present invention may thus provide an unexpectedly powerful diagnostic tool that is capable of not only identifying the general trend of IVC geometry changes, but also distinguishing, in real time, changes in IVC geometry caused by respiratory and cardiac function.

RC-WVM implant design considerations and alternative implant embodiments

It will be appreciated that measurement of the dimensional change of an IVC presents unique considerations and requirements arising from the unique anatomy of an IVC. For example, IVC is a relatively low pressure, thin walled vessel that not only changes in diameter, but also changes in overall shape (cross-sectional profile) in correspondence with changes in blood volume and pressure. IVC does not expand and contract symmetrically around its circumference, but rather expands and collapses primarily in the anterior-posterior direction from a relatively circular cross-section at higher volume to a flattened elliptical cross-section at lower volume. Thus, embodiments of the RC-WVM implant 12 must monitor this asymmetric low pressure collapse and expansion in the A-P direction without excessive radial constraint, and must also engage the vessel wall with sufficient force to securely anchor the implant and prevent migration. Thus, the RC-WVM implant 12 must be capable of collapsing in the A-P direction with the vessel from a generally circular cross-section to an elliptical or flattened cross-section without excessive distortion of the natural shape of the vessel. These requirements are achieved according to the various embodiments described herein by appropriately selecting the material compliance and configuration so that the coil measurement section of the RC-WVM implant 12 maintains contact with the IVC wall without undue radial pressure that may cause it to distort. For example, the RC-WVM implant 12 according to the embodiments described herein may exert a radial force in the range of about 0.05N-0.3N at 50% compression. In another alternative, a possible increased safety of positioning may be achieved without compromising the measurement response by physically spacing the anchoring section and the measurement section so as to move the possible distortion of the vessel wall due to anchoring to a sufficient distance from the measurement section so as not to affect the measurement.

The RC-WVM implant 12 as described may be configured in various configurations, such as a collapsible ring or tube formed from wire having a resilient sinusoidal or "Z-shaped" bend, or in a more complex collapsible shape in which more resilient regions (such as "ridges") are joined by relatively less resilient regions (such as "ears"). Each structure is configured based on size, shape, and material to maintain its position and orientation via a bias between the resilient elements of the implant to ensure contact with the vessel wall. Additionally or alternatively, anchors, surface textures, barbs, scales, pin spikes, or other fastening components may be placed on the structure to more securely engage the vessel wall. Coatings or coverings may also be used to promote tissue ingrowth. In some embodiments, it may be preferable to configure certain portions of the structure (e.g., coil spines) to position the retention engagement portions so as to reduce any effect of the biasing force on the movement of the vessel wall as sensed at the coil ears, or vice versa. In other embodiments, a separate anchoring structure may be coupled to the coil measurement portion of the implant. These anchoring structures may include hooks, expandable tubular elements, or other tissue engaging elements that engage the vessel upstream or downstream of the coil portion so as to minimize any interference with the natural expansion or contraction of the vessel in the region of the coil itself. Sensing modalities and positioning are described in more detail below.

When the RC-WVM implant 12 is energized, it must generate a signal of sufficient strength to be wirelessly received by an external system. In the case of a variable inductance circuit, the coil that transmits the signal to the external receiver must maintain a tubular shape or central antenna bore of sufficient size, even when the vessel collapses, so that its inductance is sufficient to generate a field strong enough to be detected by the external antenna. Thus, in some embodiments, it may be desirable for the variable inductor to have a collapsed portion that deforms with expansion and collapse of the blood vessel and a non-collapsed portion that deforms relatively little when the blood vessel collapses and expands. In this way, a substantial part of the coil remains open, even when the vessel collapses. In other embodiments, the coil may be configured to deform in a first plane containing the anterior-posterior axis and deflect relatively less in a second orthogonal plane containing the medial-lateral axis. In other embodiments, a first inductive coil may be provided that expands and collapses with the vessel, and a separate transmit coil that deforms substantially less to transmit a signal to an external receiver may be provided. In some cases, the transmitting coil may also serve as an anchoring portion for the implant.

Turning to the specific alternative RC-WVM implant embodiments disclosed herein, a first exemplary alternative embodiment is the RC-WVM implant 12s shown in fig. 11A, 11B, 11C and the alternative anchor 48s shown in fig. 14A, 14B, and 14C.

The RC-WVM implant 12s utilizes PTFE coated gold litz wire 42s wound on a nitinol wire frame 44 s. PTFE has good heat resistance to withstand the manufacturing process while being biocompatible. The overall configuration of the implant 12s includes a support section 38 and a crown section 40 substantially as described above. Alternatively, as described below, anchor 48s is secured adjacent crown section 40. The section of heat shrink tubing 61s is used to help ensure compression of the reflow material and may be removed in a later assembly step. A section of heat shrink tubing 60s may be used to cover and insulate the capacitor 46s, which in one embodiment may be a 47nF capacitor, or the heat shrink tubing may also be removed as described above.

The capacitor 46s may include any suitable structure to provide a desired capacitance, such as the capacitance of 47nF mentioned in one embodiment. For example, the desired capacitance may be achieved by a gap of a particular size, different terminal materials (e.g., lead wires, etc.), overlapping wires, or it may be a gap in the tube having a particular dielectric value. In the illustrated exemplary embodiment, the surface mount capacitor 46s is soldered between two terminals 56s formed by the joining of the 300-stranded litz wire 42 s. Other electrical attachments may also be employed, such as crimping or direct attachment to the terminal of the braze cap without soldering. The capacitor segment is then encapsulated using a reflow process that includes positioning a polymer reflow tube 59s over the capacitors, connections, and terminals, and then a heat shrink tube 60s is positioned over the reflow tube. The return tube 59s and heat shrink tube 60s are placed over the litz wire/nitinol frame assembly before the capacitor is welded in place (fig. 12 illustrates the return tube and heat shrink tube for the anchor, which are similarly positioned). The outer diameters of these tubes and their adapted tolerances are selected to facilitate assembly, minimize the overall profile of the final implant configuration, and optimize the flow of material to increase bond strength (bond strength). Heat is then applied to melt the polymer tube and shrink the heat shrink, thereby compressing the melted polymer over the capacitor to form a seal. Then, the heat shrinkable tube is removed. Alternative designs may employ an overmolding process, an impregnation process, epoxy potting, or the like using a suitable biocompatible material.

Details of an alternative anchor 48s are shown in fig. 14A-C. The anchor 48s is typically formed with at least two sections, an attachment section 49s where the anchor is secured to the implant and an anchor section 51s that provides fixation to the vessel wall. In some embodiments, as shown in fig. 14A-C, an additional isolation section 53s is interposed between the anchoring section and the attachment section to allow independent mechanical movement between the anchoring section and the attachment section to help isolate the action of the anchor acting on the vessel wall from the sensing function of the implant. A plurality of anchors 48s may be used in the anchoring system, with the plurality of attachment sections 49s forming attachment sections of the anchoring system and the plurality of anchors or anchor sections 48s forming anchor sections of the anchoring system.

The anchors 48s may be formed by laser cutting a pattern from a nitinol tube and shaping the anchoring barbs via a heat treatment process. Other embodiments may be formed using the following: various lines of material, shaped or bent using standard processes, or laser cut from other metals or bioabsorbable polymers. The outer surface of the anchor may utilize different shapes or different surface finishes of the anchor to engage the vessel wall and prevent migration of the implant. The overall length of the anchor 48s extending beyond the crown section 40 of the implant 12s is selected to facilitate expansion of the implant upon deployment from the delivery system 122 (fig. 9) while minimizing the effect on the movement of the implant with the vessel. This occurs as described above when the distal end of the implant is ejected from the outer sheath 124 and engages the vessel wall. The length of the anchor projection is selected to allow expansion to occur efficiently. If the protrusion is too long, the implant may not be deployed in an expanded, flowering fashion as desired. In one embodiment, the protrusion of the anchor beyond the crown section 40 (dimension D in fig. 11B) is less than the inner diameter of the outer sheath 124 of the delivery catheter.

The attachment section 49s may be formed using a tube laser cutting process to produce a helical section of tube. As indicated in fig. 12, each anchor 48s is positioned by wrapping the spiral of the attachment section around the sensor post. In one embodiment, the internal dimensions of the helical portion of the attachment section are smaller than the external dimensions of the implant strut 38 such that an interference fit is formed, securing the anchor in place. In another embodiment, the internal dimension of the helical portion is smaller than the external dimension of the terminal 56s, but larger than the external dimension of the implant post 38, and thus can be moved once wound into place on the post. In one illustrative example, the inner diameter of the attachment section helix may be about 1.156 ± 0.05mm (outer diameter about 1.556 ± 0.05mm) for an implant coil strut having a nominal diameter of about 1.143 mm. In general, the relative dimensions of the outer diameter of the implant coil and the inner diameter of the anchor helix can be selected to provide a positional interference fit.

After placement of the anchor on the implant strut, a polymeric return tube 59s is positioned over the assembly and an additional heat shrink tube 61s is placed over the assembly. Heat is then applied to melt the polymer tube and shrink the heat shrink tube, forcing the polymer between spaces in the helix of the anchoring section, thereby enhancing the fixation of the anchor to the implant assembly. The return tube 59s may also be sized to have a slight interference fit between the outer surface of the implant assembly and the inner surface of the anchor attachment section to provide some fixation of longitudinal and rotational movement during assembly. The spacing between the spirals is designed to allow the reflow material to flow into the space and form a bond. The width of the helix is designed to allow manipulation of the helical sections into position during assembly, while still providing sufficient rigidity when fully assembled. The thickness of this section is minimized to reduce the overall profile of the implant. One advantage of the attachment section 49s employing a helical portion as an attachment means is that it allows the anchor to be attached to any wire-based implant, including insulated wire implants, without interfering with or penetrating the insulation layer. The spiral portion as described distributes the attachment force over the entire space of the insulating layer to avoid damage to the layer and the space between the spirals facilitates the adhesive attachment. Another advantage of using a helical portion for attachment as described above is that the aspect ratio of the helical section can be selected to allow the helix to be slightly loosened, allowing the anchor to be placed in the middle of the implant support section without passing it past the ends of the capacitor terminals. Alternative embodiments of the attachment section 49s may take other shapes, such as a T-shape rather than a helical section, to prevent rotation and disengagement from the sensor. Further alternatives may also include replacing the polymer return tube 59s with a heat shrink that may only be left in place, or using an adhesive or other bonding technique.

As shown in fig. 14A-C, the anchoring section 51s includes two laser cut and shaped anchoring barbs 50 s. Barbs 50s are positioned on the vessel-facing surface of the anchor, and in some embodiments are angled at an angle of between about 10 to 80 degrees to provide fixation with the vessel wall, resistance to anterior and posterior implant migration, and also facilitate collapse for loading and deployment of the implant by its delivery system. The barbs 50s are shaped to point into engagement with the vessel wall and have a length sufficient to penetrate the vessel without penetrating it, typically between about 0.5 and 2.0 mm. The distal end of the anchoring section 51s may have a flat end face 47s to engage with the pusher of the deployment system and may be chamfered to avoid any sharp edges that may cause unwanted vascular reactions or get stuck on the delivery system. Other alternative embodiments may include multiple barbs or different surface treatments or barb shapes to optimize vessel fixation.

The isolation section 53s is designed to isolate or reduce the transmission of mechanical motion from the anchoring section 51s to the attachment section 49s or from the attachment section 49s to the anchoring section 51s to allow the implant to move freely and at least substantially without distortion caused by contact of the anchoring section with the vessel wall. The spacer section 53s may thus comprise a narrow cross-sectional area to provide flexibility while keeping the thickness constant to provide sufficient support. The rounded/curved surfaces as shown are maintained to avoid stress concentrations that can lead to fatigue or undesirable tissue damage. Alternative embodiments of isolation section 53s may include varying the thickness of the tube to provide greater flexibility, or varying the cross-section in a non-mirrored fashion to provide preferential flexibility in one direction.

Fig. 15A and 15B illustrate an alternative embodiment of the antenna strip module 16 s. To accommodate patients of different girths, the strap antenna 16s employs a loop antenna wire 82s mounted on or within the base layer 76s that wraps around the patient to form a discontinuous circumferential loop. The communication link 24s is provided substantially as described above. By using a loop-shaped core, the core forms a loop antenna without having to extend all the way around the patient. In this manner, a buckle or clasp (not shown) that closes the strap is also not required to provide an electrical connection to complete the antenna loop. Thus, the simplified buckle may use a variable attachment method, such as hook and loop fasteners or other attachment means, thereby eliminating the need for multiple sizes of straps. As shown in fig. 15A and 15B, the antenna strap 16s utilizes a single (or multiple) looped core wire 82s wrapped around the patient. When the substrate is wrapped around a patient, the loop ends 83s of the core 82s should be substantially adjacent, typically about 2cm to about 10cm apart. Depending on certain design parameters, the signal strength provided by the discontinuous circumferential core 82s may be less than the signal strength provided by the continuous circumferential core 82 as described above. However, the simplified clasp and ease of use provided by the antenna strap module 16s may provide usability advantages over signal requirements depending on the application and particular clinical requirements.

Relocatability of the implant or even recapture with a deployment system may be facilitated by adding recapture features in the distal end of the anchor and pusher tip, exemplary embodiments of which are shown in fig. 16A and 16B. Such recapture features allow the sensor to remain attached to the pusher while partially deployed. From this point, the mechanical means can be used to fully deploy the sensor, reposition the device while the sensor is still attached to the pusher, or recapture the device by advancing the sheath over the sensor and removing the sensor. These features may take a variety of forms, including interlocking elements, screws, or release tabs. In one embodiment, as illustrated in fig. 16A, the recapture features 127, 129 may comprise a "T-shaped" extension 127 of the anchor that engages a suitably shaped recess 129 in the distal end of the pusher 126. In another alternative, as shown in fig. 16B, the recapture features 127', 129' include through holes 127 'in the distal end of the anchor through which pin-shaped extensions 129' from the pusher 126 engage to provide engagement while remaining within the outer sheath 124. Such recapture features may be used to partially deploy the sensors while retaining the ability to reposition or recapture the sensors. The recapture feature remains engaged while the distal end of the anchor remains within the sheath. When the operator is satisfied with the final position, the sheath will be fully withdrawn, releasing the interlock feature and deploying the sensor.

Although the anchors 48s are shown in fig. 11A-C as being attached only at one end of the implant (to facilitate flowering deployment as described above), it is contemplated that the anchors may be placed at both ends of the implant, with fewer or more anchors being provided than the four shown in the figures.

In other alternative embodiments, as shown in fig. 17-29D, one or more anchoring elements that help prevent migration may be provided in an integrated anchoring frame, relative to the various anchoring elements described above. In one example, as shown in fig. 17, an RC-WVM implant including an anchoring frame 150 is attached to the RC-WVM sensor section 12 t. The RC-WVM sensor section (or simply "sensor section") 12t may comprise any of the previously described "Z-shaped" coils or similar RC-WVM implants 12 as described above, which generally include support sections 38 coupled by crown sections 40. For clarity, in the following, with reference to the embodiments described with reference to fig. 17-29D, the RC-WVM implant (or simply "implant") refers to the combined RC-WVM sensor segment and anchor frame 150. The anchoring frame 150 may be formed from a nitinol wire or laser cut tube, thereby expanding the tube to the equivalent diameter of the sensor segment. Nitinol or other materials having similar properties are well suited for use as the material of the anchoring frame 150 because it allows the anchoring frame to collapse in the loader into the same loading configuration as the RC-WVM sensor section (see fig. 9A).

Fig. 18 shows an example of the anchor frame 150 prior to attachment to a sensor segment (such as the RC-WVM sensor segment 12 t). Similar to the RC-WVM sensor segment 12t, the anchor frame 150 includes a series of straight support segments 152 (also referred to as anchor segments) that are joined by curved crown sections 154 to form a resilient concentric zigzag or linked "Z-shaped" structure that may also be considered sinusoidal in appearance. One or more anchoring barbs 156 are provided within the support section or anchoring section, as described in more detail below. The anchoring frame 150 as shown in fig. 17 and 18 includes only a single anchoring barb 156 on each support section 152. The anchor frame 150 is attached to the sensor section by attachment arms 158 that overlap the support section 152 of the sensor section. It is also noted that the crown segment 154 on the end opposite the attachment segment may be provided with recapture features, such as recapture features 127, 127', as shown in fig. 16A and 16B, that mate with corresponding recapture features 129, 129' formed on the distal end of the deployment pusher 126.

As shown in fig. 19, a polymeric return tube 160 is positioned over the attachment arm 158 and an additional heat shrink tubing 162 is placed over the return tube. As illustrated in fig. 19, the attachment arm 158 is visible through a clear return tube 160 and a heat shrink tube 162. Heat is then applied to melt the polymer return tube 160 and shrink the heat shrink tube 162, forcing the polymer between and around the attachment arms 158, thereby securing the anchor frame 150 to the RC-WMV sensor segment. The return tube 160 may be sized with a slight interference fit between the outer surface of the support section 38 and the inner surface of the return tube to provide some stability in both longitudinal and rotational movement during assembly. The attachment arm 158 may be configured to include an anchor isolation section 159. The isolation section 159 is one form of isolation device as previously described. The radial force requirements of the anchor frame 150 and the function of the isolation section 159 are also discussed in more detail below.

The attachment arm 158 may contain a serrated configuration as shown in fig. 19, wherein the spaces between the teeth 164 allow the reflow material to flow between the teeth and form a more secure bond. Other alternative configurations of the attachment arms 158 (which provide this increased surface) are believed to increase bond strength, such as zig-zag, T-shaped connectors, S-shaped connectors, and voids in the center of the post, respectively, are shown in FIGS. 29A-D. Other alternatives include surface finish or texturing on the attachment arm 158. In certain designs, such alternative configurations may allow the thickness of the attachment arms to be minimized to reduce the overall profile of the implant.

In some embodiments, such as shown in fig. 18 and 20, it may be desirable to provide a gap 166 in the anchoring frame 150 so as not to create a continuous loop of conductive material that may interfere with sensor readings. The gap 166 provides a discontinuity in the anchoring frame to prevent magnetic fields from external readers from coupling into the anchoring frame and possibly providing interference with the RC-WVM implant signal generated by the sensor segment. The slot 166 in the anchor frame 150 is advantageously located near the sensor segment, e.g., approximately in the center of the anchor frame crown 154, so that the slot in the frame does not significantly compromise the structural integrity of the anchor frame 150. In one such example, as shown in fig. 18 and 20, the slotted crown 154S is provided with dual attachment arms 158, one of which can be secured to each support section 38 on the opposite side of the corresponding implant crown section 154. In other embodiments, the slot may be located elsewhere on the anchoring frame, as described below. If desired, a double attachment arm 158 may also be provided for the seamless anchor crown 154.

In other embodiments, the decoupling slots 166 of the anchor frame may be located elsewhere on the frame, and in such cases are preferably structurally reinforced by bridging with additional metal or polymer components that provide sufficient structural integrity to the anchor frame while maintaining the discontinuous configuration. Alternatively, the continuous anchoring frame structure can be designed by carefully selecting the amount of metal material of the frame and the shape of the frame to minimize or control interference with the RC-WVM implant signal so that it can be otherwise compensated for in the signal processing.

In some embodiments, the anchor frame 150 may be attached to the RC-WVM sensor section and loaded into the deployment system, with the orientation of the anchor frame first exposed during deployment. In this case, pusher 126 of delivery system 122 is carried on crown section 40 of the sensor segment (see, e.g., fig. 9A). In other embodiments, the configuration may be reversed, with the sensor segments deployed first, and the pusher of the deployment system carried on the crown 154 of the anchoring frame 150. Orientation may vary depending on factors such as the access site of the implant (e.g., femoral and jugular veins). In another alternative, as shown in fig. 21, to improve anchoring, an anchoring frame 150 may be provided on each end of the RC-WVM implant (e.g., the sensor segment 12t), in which case the anchoring frame will be deployed first regardless of the orientation of the RC-WVM implant in the delivery system.

Once the RC-WVM implant employing anchoring frame 150 is deployed within a vessel, barbs 156 engage the vessel wall in various orientations to prevent movement of the device. Fig. 22A, 22B, and 22C illustrate one embodiment of an anchor frame 150a in which the anchor barbs 156a are disposed parallel to the anchor frame posts 152. It is also noted that anchoring frame 150 may employ two attachment arms 158 at each implant-facing crown, some of which are provided with serrations 164 and some of which are absent. In another embodiment, the planar direction of the anchoring barbs may be offset such that they correspond to the axial direction in the axial direction of blood flow within the IVC or any increment therebetween over the indicated dimensional range for the RC-WVM implant. Fig. 22C depicts the anchoring barb 156a parallel to the post 150a to which it is attached in its final shape state, but shaped such that its tip is not within the plane defined by the post and parallel barb, i.e., out of the plane of the page as shown in fig. 22C. The out-of-plane protrusions facilitate engagement of the anchoring element with the vessel wall, thereby preventing migration. The deployed configuration of the anchor is shown in fig. 22A, where the anchor is parallel to the strut 150a and thus at an angle to the direction of blood flow in the vessel.

In another example, as shown in fig. 23A, 23B, and 23C, the axially facing anchoring barbs 156B are positioned such that when the anchoring frame 150B is deployed within a blood vessel, the anchoring barbs 156B are parallel (or nearly parallel) to the direction of the blood vessel and parallel to the flow within the blood vessel. In another embodiment, as shown in fig. 24A and 24B, the anchoring barbs 156c of the anchoring frame 150c are located at the crowns 154 of the anchoring frame and are outwardly shaped to engage the vessel wall. Fig. 24A and 24B also provide examples of possible approximate dimensions of embodiments of the anchoring frame. Fig. 23C depicts the anchoring barb 156b at an angle to the post 150b to which it is attached in its final shape, and shaped such that its tip is also out of the plane defined by the anchoring barb and the post to which it is attached. This out-of-plane protrusion in both axes facilitates engagement of the anchor with the vessel wall in a better, more axial orientation, potentially providing increased migration resistance. The deployed configuration of the anchor is shown in fig. 23A, where the anchor is at an angle to the strut 150b, and thus is substantially parallel to the direction of blood flow in the blood vessel. This final positioning of the anchor tips (off the plane of the struts in both axes) can also be seen in fig. 25A.

Fig. 25A depicts an anchor frame embodiment 150a formed with straight support sections 152s between crown sections 154. The straight support section 152s may provide the following advantages: the support section is in contact with the vessel wall throughout its length, regardless of the size of the vessel in which it is deployed. When the frame is formed, for example, by laser cutting the construct from a nitinol tube, the straight configuration of the straight support segments 152s may be achieved by shaping the support segments to maintain the desired straight configuration. Fig. 25B shows an alternative anchoring frame embodiment 150B that is formed around the surface of a cylindrically shaped mandrel, resulting in a curved support section 152 c. The curved support section 152c may provide the advantage of increasing the local force with which the anchoring barbs 156 (shown as bifurcations) are pushed into the vessel wall for fixation, but may have the disadvantage that the crowns do not contact the vessel wall, particularly when the device is implanted in a small vessel.

Various orientations and configurations of the anchoring barbs 156 may be provided in different embodiments as illustrated in fig. 26A-26G. For example, as shown in fig. 26A, the anchoring barbs 156 may extend outwardly at an angle (a) of between about 10 ° and 90 ° at the center of each strut 152 of the anchoring frame 150. The anchoring barbs 156 may face alternately in one or both of the rearward or forward directions in the plane of the shaped strut 152 or extend out of that plane. In another embodiment, as shown in fig. 26B, there may be multiple anchoring barbs 156a on each strut 152 facing in each direction. A plurality of anchoring barbs 156a are located on one side of the strut 152 facing in the opposite direction as shown in fig. 26B, while in fig. 26E the anchoring barbs are on the opposite side of the strut facing in the same direction. In another embodiment, as shown in fig. 26C and 26D, the anchoring barbs 156B are contained within the thickness of the strut 152, rather than on the sides of the strut as shown, for example, in fig. 26A and 26B. The anchoring barb arrangement shown in figures 26C-D may be formed in a manner similar to anchoring barb 50s shown in figures 14A-C and described above.

In other embodiments, in the example shown in fig. 26E-H, the anchoring barbs 156 may have differently configured overall shapes and/or points, which may facilitate insertion and retention of the anchoring barbs within the vessel wall in various clinical situations. Fig. 26E illustrates a single forked barb 156c and fishhook barb 156d facing in the same direction, positioned on opposite sides of the strut 152. Fig. 26F, 26G, and 26H show additional examples of anchoring barb designs, in this case serrated barbs 156e, twoedged barbs 156F, and double sided hook barbs 156G, respectively. These barbs may be located on the sides of the anchor frame posts and also within the thickness of the posts as described above.

As described above, it may be desirable to configure the anchoring frame 150 such that it does not form a coil that may interfere with the RC-WVM implant signal. As mentioned above, one solution is the gap 166. In other embodiments, for example, where other design considerations may make the discontinuity less preferred such that the anchor frame wire is mechanically and electrically coupled (e.g., a crimp joint), the ends of the wire terminals that are coupled to and in contact with each other may be electrically insulated so as not to form a coil that is capable of coupling with a magnetic field. An example of such insulation is a polymer coating. In other embodiments, for example, where the anchoring frame may be formed of nitinol laser cut tubing, a mechanical coupling or bond may be required for this, the terminals of the nitinol frame may be physically and electrically separated by using a non-conductive adhesive (such as a polymer, epoxy, or ceramic material). Fig. 27 shows such a non-conductive coupling in cross section. In this example, end 170 of anchor frame 150 has an interlocking portion that may be bonded with a non-conductive adhesive 172, which non-conductive adhesive 172 also surrounds the joint for added strength.

As previously discussed, the radial force exerted by the RC-WVM implant should cause the sensor segment to move with the natural motion of the IVC as it expands and contracts due to changes in fluid capacity. The anchoring frame 150 is configured to apply an outward radial force sufficient to ensure engagement of the anchoring barbs 156 into the vessel wall to help prevent migration along the vessel without interfering with the motion and electrical performance of the RC-WVM sensor segment. Thus, the radial force exerted by the anchoring frame 150 may generally be equal to or higher than the radial force exerted by the sensor segment of the RC-WVM implant in order to provide migration resistance while being substantially isolated from the lower radial force sensor segment by the isolation segment 159, which is configured to allow the IVC to naturally expand and contract in response to different fluid conditions.

The isolation section 159 allows for attachment between the sensor section and the anchoring frame, but also allows the sensor section and the anchoring frame to function independently of each other. Thus, the RC-WVM sensor segment may contract and expand at the monitored location within the vessel independent of expansion and contraction of the anchoring frame at the anchoring location in the vessel. One design consideration in selecting the configuration of the anchoring frame is that the radial force exerted by the anchoring frame should be sufficient to prevent migration of the RC-WVM implant, but low enough not to dilate or distract the vessel.

Fig. 28 illustrates how the radial force of the anchoring frame 150 can be adjusted or modified to control the applied radial force by changing the configuration through variations in shaped diameter, strut width, strut thickness, strut shape, crown diameter, number of crowns, strut length, material properties, distance between the sensor segment and the anchoring frame, and overall length. Another alternative to increasing the fixation of the RC-WVM implant is to provide anchoring frames on both ends of the sensor segment, as shown in fig. 21. Fig. 28 shows an alternative anchoring frame 150a having a relatively short strut 152 length, more crowns 154 (here 16 crowns instead of 8 crowns in the previous embodiment), and smaller crown diameters. The isolation section 159 is also longer so that the distance between the anchoring frame and the sensor section increases.

The configuration of the anchor frame 150a in fig. 28 is selected to address the appropriate radial forces while minimizing areas of high strain concentration that may cause fatigue life reduction. Factors that affect the amount of radial force that the anchor frame can apply without unduly affecting the sensor segments include the distance between the anchor barbs 156 and the sensor segments, which can be adjusted depending on the positioning of the anchor barbs on the strut 152 and/or by assisting in the length of the isolated isolation segments 159. In addition to varying the length of the isolation section 159, other adjustments include varying the thickness and/or straightness relative to the curved section. For example, a straight anchor isolation section 159 is shown in fig. 28 and in another example, a curved or S-shaped anchor isolation section 159 is shown in fig. 24A.

In another alternative embodiment, the anchoring frame may be configured to intentionally break and self-separate from the sensor segment over time. In this embodiment, the connection point between the anchoring frame and the sensor section, for example in the isolation section 159, is designed to break intentionally. The purpose of the intentional fracture is to completely isolate the anchoring frame from the sensor segment after the fracture. In such embodiments, when first deployed in a vessel, the anchoring frame will secure the RC-WVM implant to prevent migration. Over time, the risk of migration is reduced as the sensor segments are embedded in the tissue. Thus, the function of the anchoring frame is no longer required. Once no longer needed, this embodiment may allow the anchoring frame to be disconnected from the device without surgery.

The material and design of the isolation section 159 may be selected to provide different time periods for the fracture to occur. For example, the geometry, design, movement and material of the sensor section, isolation section and anchoring frame may be tuned such that fatigue-induced fracture occurs after/within a given time due to fatigue. Alternatively, the cleavage may be induced by external means. For example, ultrasound/RF may be used to cause the fracture by breaking the material or bond between the anchoring frame and the sensor section at a predetermined frequency or energy. In another alternative embodiment, chemically induced fracture of the isolation section 159 can be achieved by, for example, a biodegradable polymer (e.g., PLA, PCL, PLGA, PLG) or other material that acts as a bond/connection between the anchoring framework and the RC-WVM implant framework. Chemically induced cleavage takes advantage of the material properties of the biodegradable polymer, which can degrade at a controlled rate, including such things as pH, temperature, presence of microorganisms and water.

In another alternative embodiment, the anchoring frame 150 may be made of a bioabsorbable/biodegradable material such as is commonly used for bioabsorbable struts. Similar to other embodiments of the anchoring frame, the purpose of the bioabsorbable anchoring frame is to help prevent migration. Again, as the sensor segments embed into the tissue over time, the risk of migration is reduced. Thus, the function of the anchoring frame is no longer required. The material and design of the bioabsorbable anchoring frame can be selected for different periods of absorption.

The foregoing has been a detailed description of illustrative embodiments of the invention. It should be noted that, in this specification and the claims appended hereto, unless specifically stated or otherwise indicated, connectives such as those used in the phrases "at least one of X, Y and Z" and "one or more of X, Y and Z" shall mean that each item in the connected list can appear in the list in any number other than every other item or in any number in combination with any or all other items, each of which can also be present in any number. Applying this general rule, the conjoin phrases in the above example, where the conjoin list consists of X, Y and Z, should each include: one or more of X; one or more of Y; one or more of Z; one or more of X and one or more of Y; one or more of Y and one or more of Z; one or more of X and one or more of Z; and one or more of X, one or more of Y, and one or more of Z.

Various modifications and additions can be made without departing from the spirit and scope of the invention. The features of each of the various embodiments described above may be combined with the features of the other described embodiments as appropriate to provide a variety of combinations of features in the associated new embodiments. Furthermore, while the foregoing describes a number of separate embodiments, what has been described herein is merely illustrative of the application of the principles of the invention. Additionally, although particular methods herein may be shown and/or described as being performed in a particular order, the ordering is highly variable as would occur to one of ordinary skill in the art to implement aspects of the disclosure. Accordingly, this description is meant to be taken only by way of example and not otherwise limiting the scope of the invention.

Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. Those skilled in the art will appreciate that various changes, omissions and additions may be made to the specifically disclosed matter herein without departing from the spirit and scope of the invention.