阅读说明：本技术 血压测量系统和方法 (Blood pressure measurement system and method ) 是由 A·R·希尔格斯 K·H·J·德利莫雷 于 2019-03-06 设计创作，主要内容包括：一种血压监测系统用于安装在身体肢体或者指头周围,其中,电活性材料致动器的阵列提供向内的力。被最佳定位用于执行血压监测的一个或多个电活性材料致动器被识别并且这些然后用于施加压力。通过在控制所识别的一个或多个电活性材料致动器的同时执行脉搏监测,可以确定所述血压。(A blood pressure monitoring system for fitting around a body limb or digit wherein an array of electroactive material actuators provide an inward force. One or more electroactive material actuators that are optimally positioned for performing blood pressure monitoring are identified and these are then used to apply pressure. By performing pulse monitoring while controlling the identified one or more electro-active material actuators, the blood pressure may be determined.)

1. A blood pressure monitoring system comprising:

a carrier (20) having a first side, the carrier being configured for mounting at least partially against or around a body part (22), wherein the first side of the carrier faces the body part;

a plurality of electro-active material actuators (24) arranged at different lateral positions at the first side of the carrier, each electro-active material actuator of the plurality of electro-active material actuators being independently actuatable to provide a displacement and/or a force at least in a direction away from the carrier;

a pulse monitor (30) for performing pulse monitoring and outputting a pulse monitoring signal; and

a controller (32) adapted to:

actuating the plurality of electroactive material actuators (24);

identifying one or more preferred electroactive material actuators of the plurality of electroactive material actuators for use with performing the pulse monitoring;

controlling the pulse monitor to perform pulse monitoring while or just after actuating the identified one or more of the plurality of electroactive material actuators;

determining the pulse monitoring signal obtained with the pulse monitoring; and is

Determining a blood pressure from the pulse monitoring signal.

2. The system as recited in claim 1, wherein the pulse monitor (30) includes a PPG sensor.

3. The system according to any one of the preceding claims, wherein the controller (32) is adapted to identify the one or more electroactive material actuators by actuating the electroactive material actuators in a sequence and monitoring the effect on the pulse monitoring signal.

4. The system according to any one of the preceding claims, wherein each electroactive material actuator (24) comprises a beam that bends upon actuation.

5. The system of any one of the preceding claims, wherein the plurality of electro-active material actuators comprises between 2 and 20 actuators laterally spaced apart at the first side of the carrier.

6. The system according to any one of the preceding claims, further comprising a respective force propagating unit (40) attached to each electroactive material actuator (24).

7. The system of any one of the preceding claims, wherein the identified one or more electro-active material actuators includes at least one electro-active material actuator identified as being adjacent to an artery and at least one diametrically opposed electro-active material actuator for enhancing a compression effect.

8. The system according to any one of the preceding claims, further comprising a pressure sensor (34) for monitoring pressure applied by the array of electroactive material actuators.

9. The system of claim 8, wherein the pressure sensor comprises a set of pressure sensing elements, wherein at least one pressure sensing element is associated with each electro-active material actuator.

10. The system of claim 9, wherein the controller is adapted to operate each electro-active material actuator to perform a pressure sensing function such that each electro-active material actuator functions as its own pressure sensing element.

11. The system according to any one of the preceding claims, wherein the carrier (20) is flexible.

12. A method of controlling a blood pressure monitoring system, comprising:

a carrier (20) having a first side, the carrier being configured for mounting at least partially against or around a body part (22), wherein the first side of the carrier faces the body part;

a plurality of electro-active material actuators (24) arranged at different lateral positions at the first side of the carrier, each electro-active material actuator of the plurality of electro-active material actuators being independently actuatable to provide a displacement and/or a force at least in a direction away from the carrier;

a pulse monitor (30) for performing pulse monitoring and outputting a pulse monitoring signal,

wherein the method comprises the following steps:

actuating the plurality of electroactive material actuators (24);

identifying one or more preferred electroactive material actuators of the plurality of electroactive material actuators for use with performing the pulse monitoring;

controlling the pulse monitor to perform pulse monitoring while or just after actuating the identified one or more of the plurality of electroactive material actuators;

determining the pulse monitoring signal obtained with the pulse monitoring; and

determining a blood pressure from the pulse monitoring signal.

13. The method of claim 12, comprising:

(50) independently actuating the plurality of electroactive material actuators and performing pulse monitoring, thereby identifying the one or more preferred electroactive material actuators that are optimally positioned for performing pulse monitoring.

14. The method of claim 13, wherein identifying the one or more electroactive material actuators comprises actuating the electroactive material actuators in a sequence and monitoring an effect on a pulse monitoring signal.

15. A computer program comprising computer program code means adapted to implement the method of controlling the system of any of claims 12 to 14 when said program is run on a computer.

Technical Field

The invention relates to a blood pressure monitoring system, a blood pressure monitoring method and a computer program product for performing said method.

Background

There is an increasing need for non-interfering health sensing systems. In particular, there is a shift from traditional hospital treatment towards individual-centric non-interfering vital sign sensor technologies to provide better information about the general health of the body.

Such vital signs monitoring systems help to reduce treatment costs and improve quality of life through epidemic prevention. Improved physiological data may be provided to a physician for analysis in an attempt to diagnose general health of the body. Vital signs monitoring typically involves monitoring one or more of the following physical parameters: heart rate, blood pressure, respiratory rate, and core body temperature.

In the united states, approximately 30% of the adult population has hypertension. Only about 52% of this population have their condition controlled. Hypertension is a common health problem that has no obvious symptoms and can ultimately lead to death, and is therefore often referred to as a "silent killer. The risk of blood pressure generally rising with age and becoming hypertensive later in life is quite high. Approximately 66% of people in the 65-74 age group have hypertension. Persistent hypertension is one of the key risk factors for stroke, heart failure and increased mortality.

The condition of hypertensive patients can be improved by lifestyle changes, healthy dietary options and medications. Especially for high risk patients, continuous 24 hour blood pressure monitoring is very important and systems that do not impede ordinary activities of daily living are clearly desirable.

Blood pressure is typically measured as two readings: systolic and diastolic pressures. Systolic pressure occurs in the arteries during the maximum contraction of the left ventricle of the heart. Diastolic pressure refers to the pressure in the arteries when the heart muscles rest between heartbeats and refill with blood. The normal blood pressure was considered to be 120/80 mmHg. One can consider an artificial hypertension when the blood pressure is above 130/90 or 140/90mmHg (depending on the guidelines followed), and for increased blood pressure levels, two phases of hypertension can be defined, where hypertension crisis is are defined when the blood pressure reaches 180/110 mmHg. Note that 760.0mmHg is equal to 101.325kPa (1mm Hg 133.32Pa) in order to convert these values into metric equivalents.

There are two main categories of methods for monitoring blood pressure.

For invasive direct blood pressure monitoring, the gold standard is catheterization. A strain gauge in the fluid is placed in direct contact with the blood at any arterial site. This method is only used when accurate continuous blood pressure monitoring is required in a dynamic (clinical) environment. Real-time monitoring of blood pressure is most commonly used in monitoring medicine and anesthesia.

For non-invasive indirect blood pressure monitoring, auscultatory and oscillometric methods are known. Both of these methods use a cuff placed around the arm that is inflated at a pressure higher than the systolic pressure and then slowly deflated. The auscultation method is based on listening to Korotkoff sounds (typically by a practitioner using a stethoscope) under the cuff that appear when the cuff pressure equals the systolic pressure and disappear when the remaining pressure equals the diastolic pressure. The oscillometric method is based on measuring (electromechanical) pressure oscillations. These occur when the pressure in the cuff equals the systolic pressure, they are at a maximum at the mean pressure, and they disappear at the diastolic pressure.

In order to use a clamp or cuff to determine the blood pressure (with the help of a suitable pressure sensor), a device is needed which is capable of pressurizing the cuff or (part of) the clamp to the required pressure and/or which is capable of delivering the required pressure change.

Typically, compressor-like devices are used to deliver the required pressure. Such devices are often unsuitable due to the requirement for a blower-like device that requires a cuff pressure of at least 100mmHg (about 13kPa) above atmospheric pressure. Typical pumps used for this purpose operate, for example, at currents of 6V and about 400mA and generate, for example, up to 55dB (at 30cm from the pump) of noise.

To avoid the need for an inflatable cuff, it has been proposed to perform blood pressure measurements using PPG sensors. For example, pulse wave velocity may be measured using multiple PPG sensors. Pulse Wave Velocity (PWV) is the velocity at which a pulse travels within an artery. PWV is known to be a measure of arterial stiffness and is also related to blood pressure (or Mean Arterial Pressure (MAP) or Pulse Pressure (PP)). PWV can be calculated from the pulse transit time (PTT: the time it takes a blood pulse to travel from the heart to a certain location) or more generally from the pulse delay (PD: the difference in PTT at two different locations on the body). PWV measurements can be made by measuring the time difference between pulses arriving at one location on the body (e.g., the upper arm) and another location (e.g., the wrist). By detecting the change in blood volume using a PPG sensor, a periodic signal corresponding to a pulse is obtained. PPG sensors, such as pulse oximeters, are thus typically used to provide a measurement of pulse rate.

Another way of measuring blood pressure (and without using any optical device such as a PPG sensor) is the tensiometer method. The method is based on applying a controlled force normal to the wall of the superficial artery against the bone. The force sensor measures pressure when in contact. This action on the superficial artery creates a local occlusion. A surrounding cuff is not required but instead a support device to which an impulse can be applied is required. The force applied must be small in order not to close the artery completely, since in this case the blood pressure is not measured and there is a risk of ischemia. The applied force varies to follow the pulse-pressure wave.

For correct measurement, it is important to position the tensiometer over the centre of the artery and to apply the force. The difference between correct placement and incorrect placement is in the millimeter wave regime. When the sensor is placed incorrectly, it will result in a non-linear effect of the blood pressure on the sensor. As a result, blood pressure will not be measured correctly. The tensiometer is thus highly sensitive to movements, so it requires continuous accurate positioning of the sensor. Thus, the tensiometer is normally performed when the object is stationary. Accuracy typically decreases rapidly over time and during daily activities, the device is very uncomfortable for the subject.

There are also cuff-based systems that utilize PPG measurements of the pulse. For example, in SH Song et al, Computers in medicine 2009; 36; the combination of PPG measurements with an inflatable Wrist cuff has been proposed in the article "assessment of Blood pressure using Photoplethysmography on the Wrist" 741-744. Again, this requires a compressor-like device to deliver the required pressure.

Finger-based cuffs with PPG measurement for determining blood pressure are also known and commercially available in practice, where the applied pressure is controlled to maintain a constant PPG signal. These typically operate at high pressures to provide partial occlusion of blood flow.

All these solutions have different problems associated with them, so that there is still a need for a low cost, low noise, compact and non-invasive way of measuring blood pressure.

US 2017/3687597 discloses a blood pressure monitoring system and method in which an actuator is used to apply pressure to a finger or wrist. The transfer function between the applied pressure and the measured pulse signal (e.g. using a PPG sensor) is used to derive a blood pressure measurement.

Disclosure of Invention

According to an example of an aspect of the present invention, there is provided a blood pressure monitoring system as defined in the independent claim.

The invention provides a blood pressure monitoring system, comprising:

a carrier having a first side, the carrier being configured for mounting at least partially against or around a body part, wherein the first side of the carrier faces the body part;

a plurality of electro-active material actuators arranged at different lateral positions at the first side of the carrier, each electro-active material actuator of the plurality of electro-active material actuators being independently actuatable to provide a displacement and/or a force at least in a direction away from the carrier;

a pulse monitor for performing pulse monitoring and outputting a pulse monitoring signal; and

a controller adapted to:

actuating the plurality of electroactive material actuators;

identifying one or more preferred electroactive material actuators of the plurality of electroactive material actuators for use with performing the pulse monitoring;

controlling the pulse monitor to perform pulse monitoring while or just after actuating the identified one or more of the plurality of electroactive material actuators;

determining the pulse monitoring signal obtained with the pulse monitoring; and is

And determining the blood pressure according to the pulse monitoring signal.

The system thus comprises a carrier for mounting at least partially against or around a body part, such as the neck, limbs (arms or legs) or fingers/fingers. The carrier has a first side on which actuators are arranged at different lateral positions. Thus, the positioning is such that different actuators of the plurality of actuators are located at different spatial or even angular positions with respect to the contour/circumference of the body part when the carrier is mounted against or around the body part. With respect to the carrier, the actuator thus faces inwardly from the carrier.

Each electroactive material actuator is independently controllable/actuatable to provide a displacement and/or force in at least a direction away from the carrier. This means that at least a component of the force generated by the actuator can be provided towards the body part when the carrier is positioned against or around the body part. They can thus be actuated inwardly in response to actuation and that actuation means that a force or pressure is applied to the body part.

The system includes a pulse monitor for performing pulse monitoring and outputting a pulse monitoring signal.

A controller is provided that is capable of actuating the actuators and controlling the pulse monitor such that one or more of the plurality of actuators are actuated while the pulse monitor is monitoring. Thus, during the pulse monitoring, the one or more actuators that are actuated provide pressure to the body part. Thus obtaining a pulse monitoring signal when the actuation is performed or just after the actuation is performed.

The controller can provide the pulse monitoring signal, for example for further manipulation by the controller or other device, or for communication to a user through a user interface such as a display or sound providing device.

The system and/or controller may be adapted to determine a blood pressure from the pulse monitoring signal and output the determined blood pressure result for further manipulation or output to a user using a user interface. The controller of the system may be adapted for this purpose. A user interface, such as a display, may be present to provide the pulse monitoring signal and/or the blood pressure to a user. Alternatively or additionally, the system may have a data transmission unit connected wirelessly or by wire to a remote control device, such as a processor or a computer, for providing the pulse monitoring signal to the processor or remote control device, which in turn is configured to determine the blood pressure from the transmitted data and to output the data and or the determined blood pressure to a user interface, such as a display.

The pulse monitoring provides a signal that varies depending on the pressure applied by the actuation of one or more of the plurality of actuators. Thus, actuation may be employed to investigate the blood pressure. For example, much like some of the known methods described herein before, the pressure applied with actuation may be used/adjusted to extinguish the pulse signal in order to find or determine a characteristic of the blood pressure. The reoccurrence of the pulse signal is for example related to the systolic blood pressure. The diastolic blood pressure may be determined based on an analysis of the pulse signal shape.

The disclosed arrangement utilizes a type of cuff formed from a carrier comprising an electro-active material actuator to apply pressure to the body part (such as a limb or digit) around which the carrier or cuff is attached or attached. The carrier as defined herein is advantageous for use with a blood pressure monitoring system. It enables low noise operation and compact or non-bulky devices so that even less invasive solutions are provided for blood pressure monitoring. The independent controllability of the actuators means that only those actuators are used which are needed to provide the pressure at the appropriate location. This may provide improved comfort during use.

The controller may be further adapted to be able to identify one or more preferred electroactive material actuators of the plurality of actuators for use while performing blood pressure monitoring. Preferred multiples are electroactive material actuators such as those that yield improved signal stability or sensitivity during measurement. Such preferred electroactive material actuators may be those having an improved or optimal position with respect to a position on the body part. These actuators are identified during a calibration procedure that involves identifying the preferred (best used) actuator. In this way, the subsequent control of the actuator is more comfortable, since local pressure may be applied near the location (which may be related to the location of the artery) rather than around the entire body part.

The system may for example be used for fitting around a finger, wrist, arm or leg.

The system may be used as a wearable micro system for continuous blood pressure measurement. It avoids the need for a large volume air pump and can make pressure changes quickly. Even finger-based systems with small cuff volumes would require a relatively powerful pump and thus have high power consumption to inflate the cuff and adapt to the pressure. The system of the invention has low power consumption and can also operate with very low noise.

The pulse monitor preferably comprises a PPG sensor. This provides a low cost, compact, silent and low power monitoring method. However, other parameters related to pulse may be measured, such as oxygen saturation level, SpO 2.

The pressure applied by a given level actuation of the actuator may be based on factory calibration. To account for different possible finger or limb sizes, the actuator may be advanced until contact is made, and then additional actuation is related to the applied pressure.

The controller is adapted to identify one or more electroactive material actuators, for example, by sequentially actuating the electroactive material actuators and monitoring the effect on the pulse monitoring signal. The sequence may for example comprise a circumferential sweep of the actuator while monitoring the effect on the pulse monitoring signal.

This may be performed once, for example, as a calibration step when the system is adapted. However, it may also be performed periodically to take into account possible movements of the system over time, or different limb positions may be changed for the mapping between actuator levels and the actual applied pressure.

Each electro-active material actuator may include a beam (beam) that bends inward when actuated. This provides a simple way of providing inward deflection. The beam may be fixed at one or both ends. It may also be in a freely suspended form held in place within the carrier using a sliding bracket or the like.

The plurality of electroactive material actuators may be arranged as an array of actuators. The plurality or array may for example comprise between 2 and 5, between 2 and 10 or between 2 and 20 or more actuators. In a suitable range of the previously mentioned number of actuators, the minimum number of actuators 2 may be increased to 5 or even to 10. Preferably, there are more than 4 actuators or even more than 8 actuators. The number of actuators may depend on the size of the carrier, e.g. on whether it is for a finger, wrist, arm or other body part. The solution may be such that one actuator will be sufficient to apply pressure to the arterial site and the actuators are sufficiently close together that pressure can be applied to any point.

The plurality of actuators, or at least a portion thereof, may be spaced along the length of the carrier, wherein the length is along the direction of bending (around a body part such as a finger, leg, arm or other digit) when in use. Alternatively or additionally, there may be actuators spaced apart in the width direction (perpendicular to the length direction). The width direction may be a direction in which the carrier is substantially not bent when used against a body part such as a finger, leg, arm or other digit. The actuators are thus laterally spaced apart at the first side of the carrier (and typically the interior of the carrier when mounted around the body part).

The carrier may have a cylindrical shape at least in use (i.e. mounted around or against a body part), wherein the cylindrical portion has a cross-section having a radial dimension and a width dimension, the width dimension being a direction in which the carrier does not substantially bend when mounted around the body part. The actuators may have a bending direction along which the others bend upon their actuation. They may be attached to the carrier with the bending direction being parallel to the width direction, perpendicular to the bending direction or at an angle to the bending direction (e.g. between 10 and 80 degrees or between 20 and 70 degrees). Combinations of one or more of these directions are also possible. When many actuators having a considerable size are to be mounted, which need to be juxtaposed to each other in a small circumferential cross section of the carrier, it is advantageous to have the bending direction not perpendicular to the width dimension of the carrier.

The system may further include a respective force propagation unit attached to each electro-active material actuator. The force spreading unit may have subunits, each of which is associated with at least one actuator or at most one actuator. Alternatively, there may be one such unit that is flexible and associated with all of the plurality of actuators. The actuator may provide a single point of contact at which pressure is applied. The force spreading unit ensures that pressure can be applied to all positions around the circumference of the limb or digit.

The identified one or more electroactive material actuators (i.e., those most suitable for blood pressure measurement) may include at least one electroactive material actuator identified as being proximate to the artery and at least one diametrically opposed electroactive actuator to enhance the compression effect. In this way, by implementing the nip-type compression, the pressure can be applied to a desired position more reliably.

The system may further include a pressure feedback system, such as a pressure sensor for monitoring the pressure applied by the array of electroactive material actuators. This enables a mapping between the actuation level and the actual pressure applied, so that the blood pressure level can be determined more accurately. Pressure sensing also enables identification of the point at which actuation of the actuator results in initial contact all around the limb or digit.

The pressure sensor may comprise a set of pressure sensing elements, wherein at least one is associated with each electro-active material actuator. This enables local pressure sensing feedback.

The controller may be adapted to operate each electro-active material actuator to perform a pressure sensing function such that each electro-active material actuator functions as its own pressure sensing element. This approach takes advantage of the possible sensing functionality of some types of electroactive material actuators. The pressure sensing function can even be used as a pulse monitor by detecting skin palpitations.

The carrier may be flexible, e.g. elastic and stretchable. This may, for example, enable the carrier to be adapted for contact with limbs or fingers of various sizes, such that initial actuation of the actuator results in applied pressure. The carrier may also comprise a plurality of rigid parts movably connected to each other to form what may be said to be a chain.

The invention also provides a method of blood pressure monitoring using a blood pressure monitoring system mounted around a body limb or digit, wherein the system comprises a carrier and an array of electroactive material actuators facing inwardly from the carrier at different angular positions around the interior of the carrier,

wherein the method comprises the following steps:

independently controlling the electro-active material actuators to displace inward and monitor the pulse to identify one or more electro-active material actuators that are best positioned for performing blood pressure monitoring; and

performing pulse monitoring while applying pressure using the identified one or more electroactive material actuators, and thereby determining blood pressure.

The method identifies the most suitable actuator or set of actuators before performing blood pressure monitoring using the actuator or set of actuators.

The pulse monitoring may include PPG sensing.

Identifying the one or more electroactive material actuators includes, for example, actuating the electroactive material actuators in a sequence and monitoring an effect on the pulse monitoring signal.

The method may be implemented at least in part in computer software. The software can then perform the method by controlling the controller to cause it to perform the method using the system.

The method may comprise the steps of mounting the device on a body part and determining the blood pressure.

Drawings

Examples of the invention will now be described in detail with reference to the schematic drawings in which:

FIG. 1 illustrates a known blood pressure monitoring system;

fig. 2A to 2C show examples of a carrier with an actuator in a blood pressure monitoring system;

FIG. 3A shows an overall blood pressure monitoring system using the sensor component of FIG. 2;

FIGS. 3B and 3C illustrate examples of possible positions of the pressure sensor with respect to the actuator;

FIGS. 4A and 4B illustrate the use of additional contact elements associated with each actuator;

fig. 5A and 5B show different orientations of the actuator with respect to the width direction of the carrier of the system.

Fig. 6 shows a blood pressure monitoring method.

Detailed Description

Embodiments and examples of the present invention will be described with reference to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems, and methods of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings. It should be understood that the figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the figures to indicate the same or similar parts.

A blood pressure monitoring system for fitting around a body limb or digit is disclosed in which an array of electro-active material actuators provides an inward force, i.e. a force directed towards the body limb or digit. One or more electroactive material actuators are identified that are optimally positioned for use with performing blood pressure monitoring and these are then used to apply pressure. By performing pulse monitoring while controlling the identified one or more electroactive material actuators, blood pressure may be determined.

As mentioned above, partial occlusion procedures for measuring blood pressure using a finger cuff are known. This is known, for example, as a volume clamping method and is known from "A review of methods for non-innovative and continuous air-flow compression monitoring? "(sciences direct, 2014).

By way of example, fig. 1 shows a known arrangement of a cuff 10 placed around a finger 12 with a PPG sensor for measuring pulse signals, comprising a light source 14 and a detector 15. The controller 16 controls the application of pressure to the cuff to maintain a constant flow of blood under the cuff during each heartbeat. The PPG sensors 14, 15 do not provide a blood pressure value but represent a change in the blood volume in the artery. Unfortunately, these volume changes cannot be converted into pressure values due to the non-linearity of the elastic component of the arterial wall. Based on the change in blood volume, the pressure in the cuff also changes. The solution is to make the blood volume constant below the cuff. The blood pressure value may then be evaluated as the pressure value in the cuff. Thus, the continuously changing pressure applied from outside the finger corresponds to the intra-arterial pressure and thus it is an immediate continuous measure of the arterial blood pressure.

Although the volumetric clamping method has drawbacks, in particular the reasonably high pressure applied to the tissue together with the high frequency of pressure oscillations causing discomfort to the patient, it is an attractive solution for continuous blood pressure monitoring in certain applications, such as interventions for example. Thus, several products are available that operate using this scheme.

An improvement proposed to these systems is to apply a pre-pressure in the range of systolic blood pressures and then adjust this pressure by a relatively small amount based on a PPG signal measured simultaneously by evaluation. This avoids the need to apply high pressures.

However, as explained above, there are problems associated with the use of pressure cuffs.

Fig. 2A shows an example of physical sensor components of a blood pressure monitoring system according to an example of the invention.

The sensor component comprises a carrier 20 for mounting around a body part such as a body limb or a finger. The example shown is intended to fit around a finger 22 and for this purpose has a radius according to the size of the finger. The carrier may be configured to be movable with respect to the body part. It may have suitable fastening means or devices for this purpose. It may also be part of a retractable strap that can be placed around a body part. Other ways of attaching the carrier to the body part may be employed.

The array of electroactive material actuators 24 is provided at different spaces facing inwards from the carrier 20, and in this case also at angular positions around the inside of the carrier. Each electro-active material actuator 24 is independently controllable to displace inwardly in response to an actuation signal. The solid lines represent the non-actuated configuration of the actuator and the dashed lines represent the actuated configuration of the actuator. As can be seen in fig. 2A, in the context of the present invention, the term "inwardly" means that the actuator is arranged to be able to provide a force component and/or a displacement component along the radial direction R and/or at least towards the enclosed finger. For clarity, only one example of a radial direction is shown.

Each electro-active material actuator 24 comprises a beam fixed at both ends (a double clamping arrangement) such that it bends inwardly when actuated as shown. This provides a simple way of providing inward deflection of the actuator against the finger. The actuators comprise, for example, electroactive polymer actuators (examples of which are described herein below), and they may comprise rectangular and/or elongate beams. Shapes such as square, circular, oval, etc. are also possible. Other clamping arrangements or clamping around the entire circumference (e.g., for circular/elliptical actuators) are also possible. The actuator may have a pre-bend, depending on the requirements. The entire actuator array may be incorporated into a rigid, semi-rigid, or rigid carrier 20, such as a loop or bandage-like configuration secured with hook and loop fasteners. However, the carrier may also be flexible, but not stretchable.

The example shows 8 actuators located around the circumference of the carrier. More generally, there may be between 2 and 20 actuators or more spaced around the interior of the carrier. Preferably there are at least 4. The number of actuators will depend on the size of the system (and may be determined by use on a particular body part) and/or the required ability and/or accuracy of the pressure providing device. In this example, the actuators are together designed such that pressure is applied around the circumference so that pressure can be applied no matter where in the finger the artery is located. This provides freedom to install the device while being able to provide pressure to a preferred location without requiring a location. The solution may be such that one actuator will be sufficient to apply pressure to the arterial site.

While having actuators around the circumference may provide the best flexibility to the device for the reasons indicated above and/or in terms of the utility of freedom of orientation of the device around a body limb after it is installed, actuators located around the entire circumference of the carrier are not required. This may reduce the complexity of the device. Fig. 2B and 2C show examples in which only a portion of the circumference has an actuator. In the example of fig. 2B, there is a set of contiguous actuators (4 total) covering half of the circumference of the carrier 20, which part is to be placed around the finger or other body part to be measured, so that at least one artery 26 is within the portion of the circumference covered by the actuators. The user, in particular a medically trained user, can install the device in this way with little effort. The actuators are adjacent to each other to cover an extended circumferential area, so that installation is relatively easy and the best one or combination of actuators can be used/found for providing pressure during monitoring. The part of the circumference not covered with actuators will be placed against the body part for measurement. This part of the interior of the carrier may be provided with a lining (not shown in the figures) specifically shaped to contact a specific body part in order to improve pressure distribution and/or patient comfort.

Fig. 2C shows another example of actuators on opposite sides of the circumference of the carrier. Now a reaction force is provided from the opposite side, which may improve the monitoring. There may be multiple sets of actuators located around the circumference and each of them may have at least 2 actuators or more adjacent to each other.

Fig. 3 shows an example of an overall system. In addition to the actuator array shown, for example, in fig. 2A or 2B or 2C, there is a pulse monitor 30 and a controller 32.

The pulse monitor may be a separate monitoring device from the array of actuators shown in fig. 3B. In this figure, the unwrapped pulse monitor 30 is shown pressed against a wall 36 of a body limb (e.g., a finger). The artery 38 travels along the wall. An actuator 35 as described herein above is located near the sensor 30 and is capable of compressing the artery at a location 37 to affect pulse characteristics at the location of the sensor 30. It may be a single sensor for providing a signal indicative of a pulse.

However, the sensors may instead be integrated into the structure of the array of actuators, for example as shown in fig. 3C. In this figure, the sensor 30 is mounted on an actuator 35 to press against the wall 36 of the finger to apply pressure at the location 37 of the artery 38.

If the sensors are separate from the actuators, they can be positioned between successive actuators around the circumference. Alternatively, they may be positioned next to the actuator in the width direction of the cylindrical carrier. See, for example, the discussion of fig. 5 in this regard.

There may be more than one pulse monitor throughout the system. Thus, the pulse monitor sensors may be provided, for example, on top of each actuator, or on top of a subset of the actuators. Also, the plurality of sensors may be separate from the actuator.

The or each pulse monitor is preferably a PPG sensor which generates a PPG signal "PPG", although other sensors such as a SpO2 sensor may be used.

The controller generates an actuation signal "ACT" for the actuator and outputs one or more blood pressure measurements "BP".

In a preferred example, the system further comprises pressure sensing feedback. In one set of examples, the system then further includes a pressure sensor 34 for monitoring the pressure applied by the array of electroactive material actuators and providing a pressure feedback signal "PR". This enables a mapping between the actuation level and the actual pressure applied. Pressure sensing may also enable the level of actuation at which initial contact is made everywhere around the limb or digit to be identified.

The pressure sensor 34 may include a set of pressure sensing elements, wherein at least one pressure sensing element is associated with each electro-active material actuator. The pressure sensors may be integrated in or on the physical structure of each actuator. This enables local pressure sensing feedback. The pressure sensing function may instead be implemented by the actuators themselves, if they have both an actuating function and a sensing function.

The controller performs various functions as part of an overall control algorithm. It is used to actuate an array of electroactive material actuators, but with individual control of the actuators. In particular, there is a calibration cycle in which one or more electroactive material actuators that are optimally positioned for performing blood pressure monitoring are identified. Pulse monitoring using the pulse monitor is then performed while controlling the identified one or more electro-active material actuators to apply pressure, and a blood pressure is obtained from the pulse monitoring signals.

The independent controllability of the actuators means that only those actuators are used which are needed to provide the pressure at the appropriate location. A comfortable system results in applying pressure only at the locations needed to conduct blood pressure monitoring.

The use of an actuator avoids the need for an inflatable cuff. Note, however, that the actuator may be combined with existing inflatable cuffs. The cuff may be used to provide a default pressure level and the actuator then takes over control. Alternatively, a pressure cuff may be used as the pressure sensing arrangement. For example, a small (closed) air cuff may be provided around the actuator array. The deformation of each actuator causes an increase in pressure towards the tissue but simultaneously in the small occlusive cuff. This allows, for example, known air pressure sensing methods to be used for pressure sensing feedback, for example by having an air pressure sensor associated with each cuff. Such pressure sensing can be used both to measure pressure and to detect blood oscillations.

As mentioned above, in one preferred set of examples, the pressure feedback is achieved by an actuator capable of operating in a sensing mode.

One solution is to combine the DC actuation signal with a high frequency superimposed AC signal for sensing. This solution is described in detail in WO 2017/036695. WO 2017/037117 discloses another example of sensors and actuators that enable pressure sensing as well as temperature sensing.

During actuation, the actuator generates a well-defined force and/or deformation due to an applied actuation signal, which is a voltage if the actuator is a voltage controlled actuator. The signals may also have different properties as determined by the type of actuator used. This deformation can be assumed to be known from the calibration process, even at different loads (different actuation loads are equivalent to generating different pressures to the tissue).

During actuation, the change in impedance of the actuator may also be measured as a sensing function. This impedance, in combination with the applied voltage, allows determining the (quasi-static) pressure generated towards the tissue.

In this quasi-static mode, pressure changes resulting from pulsatile blood flow can also be detected by using actuators only in the sensor mode. Palpitations (of the skin) will also deform the actuator slightly and this will change the impedance.

Thus, global slow pressure regulation and local fast pulse pressure changes can be detected. The local variations may be used to generate a desired pulse signal and the actuator may thus also be used as a pulse monitor. Alternatively, the detected pulse signal may be used as additional sensing information to the PPG signal.

The application of Pressure and the monitoring of pulse intensity or signal shape may follow known protocols, such as outlined in the above-referenced "assessment of Blood Pressure Using Photoplethysmography on the Wrist".

The applied pressure may for example be increased to cause the pulse monitoring signal to disappear. The reoccurrence of the pulse signal is for example related to systolic blood pressure. The diastolic blood pressure may be determined based on an analysis of the pulse signal shape.

The control algorithm relies on the actuation levels of the actuators and the sensed pressures in order to control the pressure applied by each of the actuators. When each actuator also acts as a sensor, once steady state is reached, the local pressure applied by each actuator can be determined and then the actuation level adjusted in order to obtain an accurate and reliable PPG measurement while ensuring patient comfort.

The control algorithm therefore functions differently than the cuff, since the pressure in the cuff is not locally changed as is achieved using a single actuator.

In the non-actuated state of the system, the actuator array can be easily placed over the finger because the actuator array is not inflated. After applying the array to the finger, it may be activated, i.e. a voltage may be applied to the individual actuator elements of the array, and thus each actuator starts to deflect. Due to the dual clamping arrangement, the only direction of movement of the actuator is towards the finger. Thus, with increasing voltage and resulting advancing movement, the tissue will be gradually compressed until the desired pressure is reached, and the voltage applied to the actuator will then not increase any further.

The arrangement of actuators shown in fig. 2 may produce a punctiform compression around the tissue. However, a more uniform pressure distribution may be beneficial.

Fig. 4A and 4B illustrate the use of an additional contact element 40 in mechanical contact (either in a stable form (e.g. glued) or in a flexible manner (e.g. via a pivot element)) with the associated actuator 24. These contact elements 40 serve as force propagation units. The force spreading unit 40 ensures that pressure can be applied at all locations around the circumference of the limb or digit. The force spreading unit 40 has a design that adapts to the tissue to be compressed, e.g. a set of concave elements that together generally match the cross-sectional shape of a finger. In fig. 4A and 4B, the units 40 are separated from each other, which gives independent freedom for operation. However, they need to be all independent. Multiple cells 40 or contiguous subsets of cells may be combined in a cell. Preferably, the unit thus assembled is flexible. All the cells may be located in a single flexible cell around the circumference of the carrier. Flexibility may provide a pseudo-independent function. The flexible material may comprise a unit with a rubber part or the like. If in the form of a single unit, it may be closed or opened in one position. The latter configuration of the plurality of cells 40 may be used with a carrier having openings with fasteners for easy installation around a body part.

Fig. 4A shows a non-activated state of the actuator and fig. 4B shows an activated state in which the force spreading unit provides a more uniform contact around the finger. The force spreading units may be made of a solid and rigid material but they may also be made of a softer or semi-rigid material in order to be slightly flexible and even better fit around the tissue to be compressed. In particular, at the ends of the force spreading unit, there may be soft areas so that they may also overlap and thus enable an adaptation to fingers of different sizes.

In an example, the carrier may have a length direction along the bending direction and a width direction perpendicular thereto. For example, in the plane of the figures of fig. 2 and 4, the length direction is along the circumference of the carrier 20. The width of the carrier is then perpendicular to the plane of the figures of fig. 2 or fig. 4.

In the above example, the actuator 24 is displaced laterally along the length direction and the beam-shaped actuator is oriented with its bending direction along the length direction. This can be difficult because the beams can be parallel to the width direction. Also, and this is not shown in fig. 2 and 4, there may be a plurality of actuators along the width direction. In the examples herein before, the actuators have been shown to be arranged parallel to the circumference of the carrier, i.e. transverse to the width direction of the carrier. This need not be the case per se. In alternative examples, one or more of the actuators are partially oriented in the longitudinal direction.

The carrier may typically have a cylindrical or part-cylindrical shape (not necessarily circular or circular in cross-section) in use. It can thus have a cross-sectional dimension (radius if a circular cross-section) and a width. In such a configuration, the width of the carrier is, for example, along direction 52 in fig. 5, and the length direction of the carrier (not shown) is along the direction of the bend or perpendicular to direction 52.

When mounted to a body part, the width direction will thus be substantially parallel to the extension of the body part (e.g. the length direction of the fingers).

Fig. 5 shows a cylindrical carrier 50 with a substantially circular cross-section. The radius R is indicated as being the width of the cylinder 52. In this example, there are two pairs of oppositely mounted actuators 54 mounted around a sub-section of the inner wall of the cylinder. Note, however, that the actuators are now substantially parallel to the width direction, their length direction (along which they bend upon actuation) being the opposite of the examples herein before. They may also be oriented with an angle 56 toward the width direction that is not 0 degrees and 90 degrees but is, for example, 30, 45 or 60 degrees. This is schematically illustrated in fig. 5B.

An advantage of the mounting in fig. 5A and 5B may be that if many actuators need to be spaced apart within a small circumferential area, this may be done without loss or with only limited loss of force and/or displacement. After all, in such a configuration, the actuators need not decrease in length size, as would be the case if an increased number of actuators oriented in the manner shown, for example, in fig. 2A were to be placed within a fixed circumferential portion. Another example would be: arteries extending in different directions through the body part under the skin can be better targeted. Combinations of different orientations are also beneficial for this purpose.

With all examples, the actuators may be distributed along the width. Thus, there may be more than one location along the width of the carrier with the actuator array in fig. 2 or 5A. This further provides a better chance of covering the artery for a good measurement. Alternatively, if there is more than one pulse sensor, there may be more arteries to measure. A comparison of the results may be performed to obtain a better estimate of blood pressure.

Again, in this configuration, the number and location of the actuators may be as previously described herein, with all of their advantages.

During the control algorithm outlined above, instead of adjusting the uniform pressure around the tissue, the pressure at one or more dedicated actuators is adjusted. Thus, only one or more actuators will change their actuation level, resulting in a point-by-point change in the pressure applied to the tissue. This may be important if only the pressure above the artery needs to be adjusted while the tissue surrounding the artery may be constantly compressed, which may improve the sensing signal and may also be more comfortable for the user.

The calibration routine for identifying those actuators includes periodic measurements of the effect of changing pressure locally around the finger or limb, so that the subsequent signal collection phase involves only adjusting the pressure at the point(s) where the best sensed signal-to-noise ratio is achieved. This may be precisely over the artery. Furthermore, one or more diametrically opposed actuators may also be addressed (and actuated with the same actuation level) in order to enhance the compression effect.

This periodic calibration may be performed at diastolic blood pressure (-80 mmHg) or lower to ensure patient comfort.

There may also be a factory calibration by which the actuator activation level is mapped to the pressure level. To account for different possible finger or limb sizes, the actuator may be advanced until contact is made, and then additional actuation is correlated to the pressure applied using the calibration data.

The overall operation of the system (without relying on additional pressure sensing feedback) can be performed in the following manner:

initially, there is no contact between the actuator and the tissue.

There is then a slow actuation of the actuator with parallel measurement of the impedance of the actuator as a feedback sensing function.

In the unloaded configuration, the impedance change according to the actuation level may be assumed to be known because of the calibration of the device before application (with calibration in the unloaded case).

Upon detecting a sudden change in impedance or any deviation from the calibration data, the actuator may be determined to be in contact with the tissue.

From this point, the look-up table can be calibrated using differently loaded actuators to generate the pre-stress required in the application. Once the pre-pressure (which is a quasi-static pressure) has been reached, the PPG signal can be determined.

As also mentioned above, separate pressure sensing feedback may be provided, for example, to make the method more accurate. The pressure sensor may also measure blood pressure directly. These pressure sensors may be implemented into an actuator array configuration. For example, at least one but preferably each actuator may be equipped with a pressure sensor such as a piezoelectric sensor, PVDF foil, or the like.

As explained above, the pressure sensing feedback may thus be based on a separate pressure sensor, an inflatable cuff for detecting pressure or the sensing function of the actuator itself.

When pressure is applied to the tissue, the pressure may be measured via the sensor. Thus, a well-defined pressure can be applied and changes in oscillations in the blood vessel can also be detected while changing the applied pressure, thereby implementing the oscillometric method. The method for example involves increasing the pressure above the systolic pressure, followed by a drop below the diastolic pressure, or alternatively starting below the diastolic pressure and increasing up to the systolic pressure.

It is noted that the device also enables a tensiometer method or a volume clamping process to be implemented. Pressure sensing may also utilize the inherent pressure sensing functionality of an actuator, particularly an electroactive polymer actuator.

The system also enables compensation of motion artifacts, e.g. caused by torsional movement of the actuator array relative to the skin surface or movement of the finger (e.g. finger kinks), which will have an effect on the size and shape of the finger at the location of the actuator array and the mechanical properties of the tissue (due to stretching/compression). The position of the actuator array may also be moved slightly along the finger. Thus, the actuator array may thus adjust the applied pressure such that pressure changes resulting from such movement will be compensated for.

Differences in finger tissue geometry may also be caused by swelling resulting from elevated ambient temperature conditions, increased salt consumption, or inflammation caused by health conditions such as osteoarthritis.

In some cases, a rigid actuator array may cause discomfort and/or suboptimal finger contact, such as too high or too low contact pressure. The carrier 20 may be made of a soft, elastic, flexible, stretchable skin-engaging material, such as silicone rubber, which can readily accommodate and compensate for natural changes in tissue geometry. This provides several additional advantages. There may be a reduction in pressure required by the actuator array for maintaining a suitable contact pressure compared to a solid embodiment. A pre-pressure (i.e. base pressure) close to the diastolic pressure may be applied by the carrier to the finger tissue, thereby enabling the actuator array to be used only for generating pressure changes. Finally, since the silicone rubber material can be textured with high contact friction, slippage of the actuator array along the fingers when worn by the user can be reduced, thus enabling it to stick to the skin in a more comfortable manner than a solid or semi-rigid material. This may help to reduce some motion artifacts.

Fig. 6 shows a blood pressure monitoring method using the blood pressure monitoring system described above. The method comprises the following steps:

in step 60, independently controlling the electro-active material actuators to displace inward and monitor the pulse, thereby identifying one or more electro-active material actuators that are optimally positioned for performing blood pressure monitoring; and

in step 62, pulse monitoring is performed while applying pressure using the identified one or more electroactive material actuators, and thereby determining blood pressure.

In all examples, the electroactive material actuator is typically based on an electroactive polymer material, but the present invention may actually be used for devices based on other kinds of EAM materials. Such other EAM materials are known in the art and one skilled in the art would know where to find them and how to apply them. A number of options are described herein below. The EAM can operate as a sensor or an actuator and can be easily manufactured in various shapes, allowing for easy integration into a wide variety of systems.

A common subdivision of EAM devices is field driven and current or charge (ion) driven EAM. Field-driven EAMs are actuated by an electric field through direct electromechanical coupling, while the actuation mechanism of current-or charge-driven EAMs involves the diffusion of ions. The latter mechanism is more common in corresponding organic EAMs such as EAP. While field-driven EAMs are typically driven using voltage signals and require corresponding voltage drivers/controllers, current-driven EAMs are typically driven using current or charge signals, sometimes requiring current drivers. These two classes of materials have multiple family members, each with their own advantages and disadvantages.

The field-driven EAM can be an organic or inorganic material, and the organic can be a single molecule, oligomer, or polymer. For the present invention, they are preferably organic and may also be oligomers or even polymers. Organic materials and in particular polymers are an emerging class of materials with growing interest because they combine actuation properties with material properties, e.g., lightweight, inexpensive to manufacture, and easy to handle.

Field-driven EAMs and thus also EAPs are typically piezoelectric and possibly ferroelectric and thus comprise a spontaneous permanent polarization (dipole moment). Alternatively, electrostriction is present and thus only includes polarization (dipole moment) when driven, but not when not driven. Alternatively, they are dielectric relaxed body materials. Such polymers include, but are not limited to, the subclasses: piezoelectric polymers, ferroelectric polymers, electrostrictive polymers, relaxor ferroelectric polymers (e.g., PVDF-based relaxor polymers or polyurethanes), dielectric elastomers, liquid crystal elastomers. Other examples include electrostrictive graft polymers, electrostrictive paper, electrets, electroadhesive elastomers, and liquid crystal elastomers.

The lack of spontaneous polarization means that the electrostrictive polymer exhibits little or no hysteresis loss even at very high operating frequencies. However, advantages are obtained at the expense of temperature stability. The relaxor operates optimally in a situation where the temperature can be stabilized within about 10 c. This may at first glance seem extremely limited, but given that electrostrictives protrude at high frequencies and very low drive fields, then the application tends to be within a dedicated micro-actuator. The temperature stability of such small devices is relatively simple and often presents only minor problems in the overall design and development process.

The relaxor ferroelectric material may have an electrostrictive constant high enough for good practical use, i.e. to facilitate simultaneous sensing and actuation functions. Relaxor ferroelectric materials are non-ferroelectric when a zero drive field (i.e., voltage) is applied to them, but become ferroelectric during drive. There is thus no electromechanical coupling in the material when not driven. The galvanic coupling becomes non-zero when the drive signal is applied and can be measured by applying a high frequency signal of small amplitude on top of the drive signal. In addition, the relaxed ferroelectric material benefits from a unique combination of high electromechanical coupling and good actuation characteristics at non-zero drive signals.

The most common examples of inorganic relaxor ferroelectric materials are: lead magnetized niobate (PMN), lead magnetized niobate-lead titanate (PMN-PT), and lead lanthanum zirconate titanate (PLZT). But others are known in the art.

PVDF-based relaxor ferroelectric polymers show spontaneous electrical polarization and they can be pre-strained for improved performance in the direction of strain. They may be any one selected from the group of materials herein below.

Polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), polyvinylidene fluoride-trifluoroethylene-chlorodifluoroethylene (PVDF-TrFE-CFE), polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene (PVDF-TrFE-CTFE), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyurethane, or a mixture thereof.

Subcategories of dielectric elastomers include, but are not limited to: acrylates, polyurethanes, silicones.

Examples of ion-driven EAPs are conjugated polymers, Carbon Nanotubes (CNTs), polymer composites, and Ionic Polymer Metal Composites (IPMCs).

Subcategories of conjugated polymers include, but are not limited to:

polypyrrole, poly-3, 4-ethylenedioxythiophene, poly (p-polyphenylene sulfide), polyaniline.

The above materials may be implanted as pure materials or as materials suspended in a matrix material. The matrix material may comprise a polymer.

For any actuation structure that includes an EAM material, an additional passive layer may be provided to affect the behavior of the EAM layer in response to an applied drive signal.

The actuating arrangement or structure of the EAM device may have one or more electrodes for providing a control signal or a drive signal to at least a portion of the electroactive material. Preferably, the arrangement comprises two electrodes. The EAM layer may be sandwiched between two or more electrodes. Such a sandwich is required for an actuator arrangement comprising an elastomeric dielectric material, because its actuation is due inter alia to the compressive force exerted by the electrodes attracting each other due to the drive signal. Two or more electrodes may also be embedded in the elastomeric dielectric material. The electrodes may be patterned or unpatterned.

It is also possible to provide the electrode layer on only one side, for example using interdigitated comb electrodes.

The substrate may be part of an actuation arrangement. It may be attached to the set of electrodes and EAP located between the electrodes or to one of the electrodes on the outside.

The electrodes may be stretchable such that they follow the deformation of the EAM material layer. This is particularly advantageous for EAP materials. Materials suitable for the electrodes are also known and may for example be selected from the group consisting of thin metal films such as gold, copper or aluminum or thin metal films such as carbon black, carbon nanotubes, graphene, Polyaniline (PANI), poly (3, 4-ethylenedioxythiophene) (PEDOT) (e.g. poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonic acid) (PEDOT: PSS)). Metallized polyester fibre films, such as metallized polyethylene terephthalate (PET), for example with an aluminium coating, may also be used.

The materials used for the different layers will be chosen, for example, taking into account the elastic modulus (young's modulus) of the different layers.

Additional layers to those discussed above may be used to adjust the electrical or mechanical behavior of the device, such as additional polymer layers.

As mentioned above, electroactive polymer structures may be used for both actuation and sensing. The most prominent sensing mechanism is based on force measurement and strain detection. The dielectric elastomer can be easily stretched, for example, by an external force. By placing a low voltage on the sensor, strain can be measured in terms of voltage (voltage is a function of area).

Another way of sensing with a field driven system is to measure the capacitance change directly or to measure the change in electrode impedance as a function of strain.

Piezoelectric and electrostrictive polymer sensors can generate electrical charge in response to applied mechanical stress (assuming that the amount of crystallinity is high enough to generate a detectable charge). Conjugated polymers may utilize the piezoelectric-ionic effect (mechanical stress results in the application of ions). CNTs experience a change in charge on the surface of the CNT when exposed to stress, which can be measured. The electrical resistance of CNTs has been shown to be in contact with gasesMolecule (e.g., O)₂、NO₂) The contact is altered so that the CNT can be used as a gas detector.

Preferred embodiments of the present invention utilize PPG sensing. Pulse oximetry is a common example of a PPG-based sensor. The purpose of pulse oximetry is to monitor the oxygen saturation of the blood of a patient. Although the purpose of such a sensor is to obtain a measurement of oxygen saturation, it also detects changes in blood volume in the skin and thus performs PPG sensing. By detecting the change in blood volume, a periodic signal corresponding to the pulse is obtained. PPG sensors, such as pulse oximeters, are thus most often used to provide a measurement of pulse rate.

The PPG sensor comprises at least one LED and one light sensor. The LED and sensor are positioned such that the LED directs light toward the user's skin, which is reflected or transmitted and detected by the sensor. The amount of reflected/transmitted light is determined inter alia by the perfusion of blood in the skin.

PPG systems, for example, include red LEDs, near infrared LEDs and photodetector diodes. The LEDs emit light at different wavelengths that is diffused through the vascular bed of the patient's skin and received by the photodetector diodes. Measuring the changed absorbance at each of these wavelengths allows the sensor to determine the absorbance due to pulsing only arterial blood (excluding, for example, venous blood, skin, bone, muscle, and fat). The generated PPG signal can then be analyzed.

Other simpler versions of the system for obtaining PPG data may be used, including versions with a single light source of one or more wavelengths. The absorption or reflection of light is modulated by the pulsating arterial blood volume and detected using a photodetector device.

In transmission pulse oximeters, the sensor device is placed on a thin portion of the patient's body. A reflection pulse oximeter may be used as an alternative to a transmission pulse oximeter. This approach does not require thin parts of the body and is therefore well suited for more general applications.

The basic design of a PPG sensor has, for example, a specific light output frequency (e.g. 128Hz), with which the light source is pulsed. The sampling frequency of the optical sensor is high, e.g. 256Hz, so that it measures during and between activation of the light source. This allows the system to distinguish between light emitted from the LED and ambient light and thereby filter the ambient light from the signal received during the pulsing of the light source.

As discussed above, the controller performs data processing. The controller can be implemented in various ways (using software and/or hardware) to perform the various functions required. A processor is one example of a controller that employs one or more microprocessors that are programmed using software (e.g., microcode) to perform the required functions. However, the controller may be implemented with or without a processor, and may be implemented as a combination of dedicated hardware for performing some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) for performing other functions.

Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, Application Specific Integrated Circuits (ASICs), and Field Programmable Gate Arrays (FPGAs).

In various embodiments, a processor or controller may be associated with one or more storage media (e.g., volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM). The storage medium may be encoded with one or more programs that, when executed on one or more processors and/or controllers, perform the required functions. Various storage media may be fixed within the processor or controller or may be transportable, such that the program or programs stored thereon can be loaded into the processor or controller.

Other variations to the disclosed embodiments can be understood by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the words "a" or "an" do not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims shall not be construed as limiting the scope.

It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention.