阅读说明：本技术 用于测量气道阻力的方法和设备 (Method and apparatus for measuring airway resistance ) 是由 奥列格·格鲁丁 罗纳德·让·丹杜兰 于 2020-03-27 设计创作，主要内容包括：一种用于使用安静呼气测量肺功能参数的装置,该装置具有流管、遮板、可控闩锁、流量传感器、压力传感器、闩锁控制器以及止回阀,流管具有嘴件端和出口,遮板覆盖流管的出口；可控闩锁关闭和释放遮板,流量传感器用于在遮板释放之后测量流管中的流量,压力传感器用于在遮板释放之前测量流管中的压力,闩锁控制器连接到压力传感器和可控闩锁；止回阀布置在流管或遮板中以用于在遮板关闭时允许吸气,使得装置能够在整个至少一个吸气和呼气周期中使用。(A device for measuring a lung function parameter using quiet expiration, the device having a flow tube having a mouthpiece end and an outlet, a shutter covering the outlet of the flow tube, a controllable latch, a flow sensor, a pressure sensor, a latch controller, and a check valve; a controllable latch closes and releases the shutter, a flow sensor for measuring the flow in the flow tube after the shutter is released, a pressure sensor for measuring the pressure in the flow tube before the shutter is released, a latch controller connected to the pressure sensor and the controllable latch; check valves are arranged in the flow tube or shutter for allowing inspiration when the shutter is closed, enabling the device to be used throughout at least one inspiration and expiration cycle.)

1. An apparatus for measuring lung function parameters, comprising:

a flow tube having a mouthpiece end and an outlet;

a shutter covering an outlet of the flow tube;

a controllable latch that closes and releases the shutter;

a flow sensor for measuring flow in the flow tube after release of the shutter;

a pressure sensor for measuring pressure in the flow tube prior to release of the shutter;

a latch controller connected to the pressure sensor and the controllable latch;

a check valve disposed in the flow tube or the shutter for allowing inspiration when the shutter is closed, such that the device can be used throughout at least one inspiration and expiration cycle.

2. The apparatus of claim 1, further comprising a calculator connected to the flow sensor and the pressure sensor for calculating lung function parameters.

3. The device of claim 2, wherein the calculator calculates the lung function parameter using data from the flow sensor up to about 150ms from peak flow after release of the shutter.

4. The device of claim 3, wherein the lung function parameter is airway resistance.

5. The device of claim 1, further comprising a data transmitter for transmitting data from the device to a computing device for calculating lung function parameters from the data.

6. The apparatus of claim 5, wherein the data comprises the flow sensor measurements from peak flow to up to about 150ms from peak flow after release of the shutter.

7. The apparatus of any one of claims 1 to 6, wherein the flow sensor is configured to additionally measure inspiratory flow.

8. The apparatus of claim 7, wherein the flow sensor comprises separate flow sensors for inhalation and for exhalation.

9. The device of any one of claims 1 to 8, comprising a latch controller connected to the controllable latch and the pressure sensor, wherein the shutter can be released at the beginning of exhalation when the pressure in the flow tube has started to increase without a forced effort.

10. The device of any one of claims 1 to 9, wherein the latch controller releases the controllable latch at a predetermined pressure.

11. The device of claim 10, wherein the predetermined pressure is defined by an external computing device.

12. The device of any one of claims 1 to 11, wherein the check valve is disposed in the shutter.

13. The apparatus of any one of claims 1 to 12, wherein exhalation flow is measured for full exhalation, the apparatus further comprising a calculator connected to the flow sensor for calculating slow vital capacity from the full exhalation after release of the shutter.

14. The apparatus of any one of claims 1 to 13, further comprising a shutter shield mounted to an outlet of the flow tube.

15. The apparatus of any of claims 1-14, further comprising a hinge connecting the shutter to the flow tube.

16. The device of claim 15, wherein the hinge is mounted such that its axis of rotation is angled relative to vertical such that gravity causes the shutter to return to a closed position.

17. The device of claim 15, further comprising a biasing member that causes the shutter to return toward a closed position.

18. In combination, a device for measuring lung function parameters according to any one of claims 1 to 17, wherein the device comprises a data transceiver and a computing device comprising a corresponding data transceiver and a memory storing a computer program for communicating with the device and providing a user interface for controlling the device.

Technical Field

The present application relates to medical diagnostic and monitoring devices, and more particularly to devices that measure respiratory parameters such as airway resistance.

Background

The diagnosis of respiratory diseases and the monitoring of their progression is based on measuring respiratory parameters. One such medically valuable parameter is airway resistance.

The interrupter or shutter measurement method is one of the techniques to determine airway resistance, which requires minimal cooperation of the subject. In this way, the subject breathes through the breathing tube. At some point, typically during exhalation, the opening of the breathing tube is briefly closed by the shutter. Within a short period of time (typically about 100ms-150ms) after closing, the air pressure in the mouth and breathing tube increases to a level that is assumed to correspond to the alveolar pressure at the moment of the interruption of the air flow. The measurement of the airflow and the accumulated pressure just prior to shutter closing are used to determine airway resistance. One variant of the interrupt technique, known as the "open" interrupt method, uses different measurement sequences. The flow rate is not measured before the interruption of the air flow but shortly after the shutter is opened. In this method, a longer interrupt period provides a more complete balance between alveolar and mouth pressure, which improves the accuracy of airway resistance measurements. According to this method, the interruption is made only during the inspiration phase and in the middle part of the inspiration phase. Mouth pressure was measured immediately prior to opening, and airflow was averaged during a period of 15ms-35ms after opening The shutter (European journal of respiration (Eur. J. Respir. Dis.), 1982, Vol. 63, p. 449-458 (198263,449-458), K. van der Plas, P. Vooren, 'open' interrupter-a new variant of The technique for measuring respiratory resistance "(" The "opening" mouthpiece. A new variable of a technical for measuring respiratory resistance ")).

Another variation of the interrupt technique during a breathing operation is described in applicant's pre-granted US patent publication US 2016/256073, in which a subject begins breathing into a flow tube initially closed by a shutter. Applicants refer to such devices and techniques as relaxed occlusion expiratory monitoring (REOM). After the accumulated pressure exceeds a certain threshold, the shutter is opened and a flow spike is measured during 100ms-150ms after shutter release. Airway resistances of the upper and lower airways are determined by analyzing the shape of the flow waveform. Airway resistance measurements may be taken after a single expiratory cycle that includes an occlusion phase and a brief flow spike post-occlusion.

Disclosure of Invention

The applicant has found that in the case of REOM, there may be some hesitation between the user or patient that the device mouthpiece is not correctly placed in the mouth due to inhalation, followed by an action of placing the mouthpiece in the mouth before starting the non-forced exhalation. Improvements to this technique are presented below in the present invention.

Switching from a single exhalation (with one interruption event) to spontaneous breathing (when the interruption occurs multiple times at the beginning of each subsequent exhalation) makes the breathing operation of the subject easier. The subject may maintain his or her mouth shape and continue to inhale and exhale in a relaxed or non-forceful manner. When a subject is focused on a single trial, spontaneous breathing is more natural than a single exhalation, and unconsciously may attempt to control his or her exhalation, which may result in the occlusion phase being too fast or too slow, and distortion of the flow waveform caused by additional effort different from that applied during full spontaneous breathing.

In prior art REOM devices, the shutter may be hinged or simply fall out of the flow tube. When the shutter operates in the continuous mode, it will return to the blocking position. The applicant has found that the measurement is not influenced by the shutter when the shutter is arranged to provide a small impedance for flow measurement after release within a period of about 200ms after release. At this point, if the shutter begins to return during exhalation, any resistance to expiratory flow is not an issue. Once exhalation ceases and inhalation begins, the shutter has a significant amount of time to return to the occluded position and latch.

In some embodiments, there is provided an apparatus for measuring a lung function parameter using quiet exhalation, the apparatus having a flow tube having a mouthpiece end and an outlet, a shutter covering the outlet of the flow tube, a shutter, a controllable latch, a flow sensor, a pressure sensor, a latch controller, and a check valve; a controllable latch closes and releases the shutter, a flow sensor for measuring the flow in the flow tube after the shutter is released, a pressure sensor for measuring the pressure in the flow tube before the shutter is released, a latch controller connected to the pressure sensor and the controllable latch; check valves are arranged in the flow tube or shutter for allowing inspiration when the shutter is closed, enabling the device to be used throughout at least one inspiration and expiration cycle.

Multiple shutter openings at the beginning of each exhalation may improve the accuracy of the measurement by:

-obtaining interrupt flow/pressure data from a plurality of interrupt events;

-rejecting certain interruption events if a brute force is detected, or the flow waveform is distorted due to voicing or other artifacts;

averaging the airway resistance measured over a plurality of interruption events, or

-averaging the plurality of post-occlusion flow waveforms, and further calculating the airway resistance of the averaged flow waveform.

Drawings

The invention will be better understood by reference to the following detailed description of embodiments of the invention with reference to the drawings, in which:

fig. 1A shows a prior art design of a flow tube with a shutter for airway resistance measurement using a pitot tube for measuring expiratory flow and a single sensor for measuring both flow and pressure.

Fig. 1B shows a prior art design of a flow tube with a shutter for airway resistance measurement using a flow sensor port and shutter arrangement for measuring expiratory flow and a single sensor for measuring both flow and pressure, where the tube cross-section at the shutter location along line a-a is shown in fig. 1C.

Figure 2A schematically presents a design of the flow tube closing the shutter at the beginning of exhalation.

Figure 2B schematically presents a design of the flow tube that opens the shutter during exhalation.

Figure 2C schematically presents a design of a flow tube with a shutter closed and a valve open during inspiration.

Fig. 2D schematically presents a variant design of a flow tube closing the shutter during inspiration, where the flow tube has an additional port and sensor for measuring inspiration flow.

Fig. 3 shows a design of a shutter with an inclined axis of rotation.

Figure 4 shows a mouthpiece of a flow tube.

FIG. 5A illustrates one of the embodiments of the device having an alternative position of the valve integrated with the flow tube.

Fig. 5B shows a schematic block diagram of one of the embodiments of the apparatus in combination with a smartphone or computing device.

Fig. 6 is a schematic flow chart describing the operation of the apparatus.

Fig. 7 shows the output signal of the pressure sensor at the end of the occlusion phase and at the beginning of the flow spike after the shutter release after occlusion.

Fig. 8 schematically presents a variant design of the flow tube similar to fig. 2D, wherein the shutter is closed during inspiration, wherein the flow tube has a shutter shield;

fig. 9 is a front view of the embodiment of fig. 8 showing the shutter guard.

Detailed Description

A prior art design of a flow tube with a shutter for a breathing apparatus for airway resistance measurement is shown in fig. 1A to 1C. The device performs the measurement of airway resistance based on one interruption event at the beginning of a single exhalation. The position of the shutter at the end of the post-occlusion spike is unimportant and uncertain. The shutter may be fully opened or closed. The only requirement is that after shutter release, the shutter remains open during a first period of time of about 100ms-150ms to provide the undistorted flow waveform needed to calculate airway resistance. However, it should be understood that the shutter does not interfere with the measurement of the post-occlusion flow spike.

Switching from a single interrupt event based mode of operation of the breathing apparatus to a multiple interrupt event based mode of operation at the beginning of a subsequent exhalation cycle may provide easier, more natural and more convenient breathing operation. The subject may breathe spontaneously in a relaxed manner without having to concentrate on a single exhalation and attempt to control the exhalation effort. Thus, the results may be more representative of the true lung capacity of the patient.

To achieve a mode of operation of the breathing apparatus based on multiple interruption events, the shutter may be configured to provide: a) free and unobstructed exhalation immediately after shutter release and during inhalation relaxation, b) blocking the flow tube at the beginning of exhalation and during the occlusion phase. This means that the shutter may return to its initial closed position at the beginning of each exhalation.

Fig. 2A shows one of the possible embodiments of a flow tube 1 with a shutter 4. When the flow tube 1 is obstructed, the position of the shutter 4 corresponds to the beginning of exhalation. The shutter 4 may have one or more openings 10 closed by a check valve 12, which check valve 12 may be made of a soft and flexible material like rubber or silicone. The magnet 15 may attract metal fragments 14 of the shutter 4, such as ferromagnetic metal clips or inserts, to prevent the shutter from opening when the pressure within the flow tube 1 increases until a desired threshold is reached during occlusion. If the cover 4 is made of a suitable metal material, no separate pieces 14 are required. Other types of latching mechanisms may be used to hold and release the shutter 4. The flexible check valve film 12 may block the opening 10 in the shutter 4 at this stage. Furthermore, it should be understood that the check valve 12 may be replaced by any other means of controlling the opening to allow airflow during inhalation and prevent airflow during exhalation, such as using an electronically controlled valve that operates based on sensor readings.

After the accumulated pressure exceeds a predetermined threshold, solenoid 16 may push shutter 4 to release it from magnet 15. The increase in the distance between the magnet 15 and the metal fragments 14 of the shutter 4 rapidly reduces the magnetic attraction force and further opens the shutter 4 by the compressed air that accumulates during the occlusion phase. When other forms of latch mechanisms are used, a different trigger or release mechanism may be used (e.g., an electromagnet may be used in place of the magnet 15, and the release mechanism of the shutter 4 may include de-energizing the electromagnet).

The full opening of the shutter 4 may take about 10ms with minimal distortion of the air flow. Fig. 7 shows a typical output signal of a sensor 8 measuring the pressure in the air channel 2 of the flow tube 1. A positive signal corresponds to the pressure during the occlusion phase (zero flow) and a negative signal corresponds to the flow after shutter release. It may take about 8ms to open the shutter 4 and reduce the accumulated pressure to zero. When the port 7 is arranged downstream of the baffle or in the pitot tube, the expiratory air flow through the tube 1 causes a negative pressure and a negative output signal of the sensor 8. The maximum absolute value of the signal may be reached about 10ms after the shutter opens and corresponds to peak flow.

As shown, the shutter 4 is a single flap type valve that opens outwardly, and is therefore pushed by the air flow leaving the flow duct 1 and moves with the air flow leaving the flow duct 1. It will be appreciated that more than one flap may be arranged to provide a releasable occlusion at the end of the flow tube 1. The movement of the flap and the release air does not adversely affect the measurement of the flow in the tube 1 by the sensor 8.

It will be appreciated that the measurement device may include circuitry for controlling latch release, measuring pressure and flow in the tube 1 from the sensor 8 readings, and optionally calculating values such as airway resistance and/or lung compliance from the readings. Such a circuit is described in the applicant's pre-empted patent publication US 2016/256073, the specification of which is incorporated herein by reference. For example, this may include a microcontroller associated with the sensor 8, and data processing may be done using an associated program or application on a connected device (e.g., bluetooth), such as a smartphone or other convenient computing device. This may allow the cost of data processing to be removed from the measurement device. As described in more detail below with reference to fig. 6, the recording of such measurements may involve multiple "trials" or collected measurements of exhalation performed during normal inhalation and exhalation without the user being forced, and the data may be averaged and/or compiled as desired.

In some embodiments, the airway resistance measurement method involves measuring flow in the range of about 100ms-150ms after the shutter opens. After this time interval, the position of the shutter 4 may not be critical for the measurement. Preferably, the shutter 4 should not prevent spontaneous exhalation by the subject once the shutter 4 is released. Fig. 2B shows the shutter 4 in a maximum opening position that may be limited by a bumper or damper 11. Bumper 11 may provide an abutment for shutter 4 when shutter 4 swings open to determine the maximum opening angle of shutter 4. The opening angle may be an important parameter of the device and will be discussed below. It should be understood that the bumper 11 may take a variety of different forms to provide the function of limiting the opening angle.

An external return force may be applied to the shutter 4 to urge it to its initial closed position. This force can be generated by a spring or by using electrostatic and magnetic principles. Gravity may also be used as shown in this embodiment. After opening the bumper 11 and colliding with the bumper 11, the shutter 4 returns to its original position, and may block the opening of the flow tube 1, preventing normal exhalation by the subject. To eliminate this possibility, solenoid 16 remains energized to prevent shutter 4 from contacting magnet 15 and leaving a sufficiently wide gap between the shutter and flow tube for exhalation. The damper 11 may also provide some elastic energy to return the shutter 4 to the closed position if desired, thus, for example, assisting with gravity or a spring mechanism.

The onset of inspiration may result in a significant negative pressure within the flow tube 1, which may be detected by the sensor 8. Upon detection of an inhalation, solenoid 16 may be de-energized and shutter 4 may stick to magnet 15 (latch closed). The check valve 12 opens allowing the subject to inhale through the flow tube 1. Fig. 2C shows the position of the shutter 4 during inhalation.

After the subject completes inhalation and begins exhalation, the positive pressure within the flow tube 1 closes the check valve 12 and a new occlusion phase begins.

Fig. 2D shows an embodiment in which an additional port 7' may be added before the flow baffle located before port 7. The port 7' may be positioned as illustrated such that the sensor 8 "may be used to measure inspiratory flow. Sensor 8 "is shown connected to measure the differential pressure across the shutter in the flow tube, and sensor 8" will then measure both inspiratory and expiratory flow. It will be appreciated that other arrangements for measuring inspiration are possible, and that the measurement of inspiration is optional if only expiratory flow is of interest. By measuring the inspiratory flow and expiratory flow during one or more respiratory cycles, the device may measure further lung parameters, such as tidal volume, slow lung capacity, etc. In measuring Slow Vital Capacity (SVC), the shutter can be kept open if desired. Different arrangements of flow sensors may be used. A single sensor may be used to measure both forward and reverse flow, while another sensor may be used to measure pressure. Measurement of the flow/volume parameters of the breath may require the fixation shutter 4 to be in a permanently open position and temporarily disable the airway resistance measurement mode.

Fig. 3 shows a front view of an embodiment in which the shutter 4 with the hinge 9 rotates around an axis 6, the axis 6 being inclined at an angle a with respect to the direction of gravitational acceleration. The dynamics of the opening and closing of the shutter 4 may depend on the following parameters:

-an angle α;

mass of the shutter 4:

the position of the damper 11 that limits the opening angle of the shutter 4.

Without a hinge, it will be appreciated that the shutter needs to be placed in a closed position prior to use, however, the check valve allows the patient to begin using the device by first completing a quiet inhalation before exhaling quietly. The quiet expiration and the stability of the resulting measurements can be improved by starting with inspiration.

In the embodiment of fig. 3, when performing SVC, the flow tube can be rotated so that gravity keeps the shutter 4 open.

By adjusting these three construction parameters, the following conditions can be satisfied. The time interval between the shutter opening and its impact with the flow tube may exceed the observation time required to measure the post occlusion flow waveform, i.e., about 150 ms. If a collision of the shutter with the flow tube occurs faster than the mentioned time, the flow disturbance caused by the collision may disturb the device measurement.

In one particular case of this device embodiment, the damper or bumper 11 may be positioned such that the opening angle of the shutter 4 is about 150 °. The angle alpha between the rotation axis and the direction of gravitational acceleration may be selected to be about 75 deg.. The experimental measurement time interval between the shutter opening and its impact with the flow tube is about 250ms, which is long enough to perform an undistorted flow waveform measurement to determine airway resistance.

After the user has started inhaling, a negative pressure is generated inside the flow tube 1 and can be detected by the sensor 8.

It will be appreciated that gravity may be used instead of or in addition to returning the shutter 4 towards the closed position by using a light spring or biasing member. If gravity or bias cannot cause the shutter 4 to seal against the end of the flow tube 1, it will be appreciated that subsequent inhalation will help close the shutter until the check valve 12 opens, and even so, a small negative pressure will exist inside the tube 1 during inhalation, which will help keep the shutter 4 closed.

After inhalation is detected, the solenoid 16 may be de-energized (normally, the release mechanism is only temporarily triggered to cause the shutter to release) and the shutter may stick to the magnet 15. The flexible membrane of the check valve 12 may flex inwardly due to the negative pressure within the flow tube 1 created during inhalation and may open the holes 10 in the shutter 4, allowing air to flow through the flow tube 1. The check valve 12 may be opened until the end of inspiration. When the subject begins to exhale, the check valve 12 closes and the occlusion phase begins.

Figure 4 shows an example of a mouthpiece 3 connected to an air channel 2 of a flow tube 1. The mouthpiece 3 includes an optional tongue depressor 5 to fix the position of the tongue, preventing it from potentially blocking the opening of the flow tube 1, distorting the air flow and adversely affecting the measurement of the breathing apparatus. Such a mouthpiece 3 may be made disposable. It may also be an integral part of the flow tube 1 and the entire flow tube 1 engaged with the mouthpiece 3 may be made disposable. Mouthpiece 3 may also be integrated with a bacterial filter.

Fig. 5A shows an alternative embodiment of the device, in which a check valve 12 closes the opening 10 in the body of the flow tube 1. In the configuration of the device, it is not necessary to attach the check valve 12 to the shutter 4 and form the hole 10 in the shutter 4.

Also shown in fig. 5A are the following options: instead of using one sensor operable for both flow and pressure, the sensor 8 may be divided into two different sensors 8 and 8' for expiratory flow and pressure, respectively. Fig. 5A also shows that the latch controller may be included in a device for controlling the release of the latch based on pressure measurements. Fig. 5A also shows that data from the sensor 8 can be transmitted to another device for processing using a data transceiver, such as a wireless link, a cable link, etc.

Although not shown, an external processing device may be used to monitor pressure during shutter occlusion and to signal a release to the latch. If the inspiratory flow is also to be measured, the flow sensors 7', 8 "will need to be arranged at the port 10.

In fig. 5B, a system is illustrated that includes a device in combination with a computing device (such as a smartphone). The computing device may comprise a processor, a memory storing a computer program for the device 1, a data transceiver for communicating with the device 1, and optionally a network interface for transmitting data and/or receiving settings from a remote party. The device may include a microcontroller or microprocessor semiconductor unit, which may include a wired or wireless transceiver for communicating with a computing device. Functions such as shutter control, access control using indicators on the device or a user interface on the computing device, data acquisition and storage, raw and/or compliance calculations, etc., can thus be implemented using the processing power of the device or the processing power of the computing device as desired.

In the exemplary embodiment of fig. 5B, the device is configured to control shutter release based on a pressure threshold, the value of which may be set, for example, by software of the computing device and/or settings of the user interface. The computing device may include software for communicating the results from the device to a Health Care Professional (HCP), and if desired, the shutter release pressure setting may be set by the HCP. Alternatively, the shutter release may be controlled from the computing device, in which case the device transmits pressure readings to the computing device every few milliseconds.

Fig. 5B also shows that the computing device may perform a flow spike waveform consistency analysis. This analysis is optional and may also be performed by the processor of the device, if desired. The consistency analysis may be a comparison of flow spike waveforms (e.g., post-occlusion flow data, typically up to about 150ms after peak flow) with respect to each other. Since the measurement can be performed at each exhalation, it is easy to acquire a plurality of waveforms. When the waveform is significantly different from other waveforms, possibly due to compulsions, coughing, vocalization, etc., the waveform may be ignored. A number of consistent waveforms and their associated flowtube pressures at occlusion release may then be used for measurements.

Alternatively, the device or smartphone may signal to the user that data acquisition has ended because a period of time or number of exhalations has elapsed and/or because many consistent waveforms have been collected. The stop signal (e.g., audible or visual) may be emitted by an indicator on the device or through a smart phone or computer.

The software in the device or computer may also be arranged to measure slow lung capacity. The measurement may begin with the user selecting a measurement or by the device and/or computer indicating to the user that the measurement is to begin. The user slowly and completely inhales followed by a slow exhalation wherein air is completely exhaled from the lungs with muscular force. The device measures the flow during this exhalation and the volume of air in the exhalation can be recorded as an SVC measurement. If the device also measures inspiratory flow, SVC measurement may involve measuring the volume of inspiration and expiration to confirm the SVC measurement by using both inspiration and expiration data. Thus, the presence of the shutter and its release pressure do not adversely affect the SVC measurement.

While the system between the device and the smartphone may be best separated as a way to provide a better user interface and reduce the cost of the device, it should be understood that the device may incorporate a user interface and may incorporate network connectivity such that the device may be completely independent of any smartphone or computer.

Fig. 6 shows a block diagram illustrating one possible embodiment of the operation of a breathing apparatus during one breathing cycle.

First, when the subject inhales, the shutter 4 is closed and the check valve 12 is opened (see fig. 2C). The transition from inspiration to expiration is accompanied by a change in the pressure inside the flow tube 1 from negative to positive, which can be detected by the sensor 8. The check valve may close automatically at the beginning of exhalation.

In a next step, the sensor 8 may measure the accumulated pressure during the occlusion phase. The solenoid 16 may be energized when the accumulated pressure inside the flow tube 1 reaches a predetermined threshold. The solenoid 16 may push the shutter 4 causing a rapid opening of the flow tube 1. As noted above, other latching mechanisms may be used without departing from the teachings of the present disclosure.

After the shutter 4 is released and when the shutter is widely opened, the post occlusion flow may be measured over a period of about 100ms-150 ms. Based on these data, airway resistance may be calculated.

An external return force may be applied to the shutter 4 after the shutter 4 is opened in order to return the shutter to its initial closed position. This force may be generated, for example, by a spring or by gravity. Other sources of external return force (like electrostatic or magnetic) are also possible. The second force counteracting the return force prevents full closure of the shutter 4 so that the patient may continue to exhale. The second reaction force may be generated by, for example, shutter 16. Shutter 16 continues to be energized, thereby maintaining a gap between the shutter and the edge of flow tube 1. Typically, when the shutter is partially closed, the pressure inside the flow tube 1 is positive during exhalation.

The transition from expiration to inspiration is accompanied by a change in the air pressure inside the flow tube 1 from positive to negative. After such a transition is detected, for example, by the sensor 8, the reaction force may be closed (e.g., the shutter 16 is de-energized) and the shutter 4 may be fully closed by the external return force. The shutter 4 may be adhered to the magnet 15. The negative pressure within the flow tube 1 may cause the check valve 12 to flex inwardly, causing the aperture 10 to open and allow air to flow through the tube 1 during inspiration.

The use of post-occlusion non-forced expiratory flow waveforms and occlusion pressure to calculate airway resistance and/or lung compliance is described in applicant's pre-grant patent publication US 2016/256073, published on 9, 8, 2016. At this stage, the raw data of the measurement of the interruption event may (optionally) be transmitted to a computer or smartphone. Alternatively, if the electronic hardware supports this mode of operation, data may be transmitted continuously during all phases of the breathing cycle.

When a computer or smartphone receives measurement data, a decision can be made in real time as to the acceptability of the measurement. For example, an abnormally short occlusion time may indicate an excessive expiratory force being applied, which may be unacceptable during an unforced airway resistance measurement. Distortions of post-occlusion flow spikes, e.g., caused by voicing or other artifacts, may also be detected. Such data may be rejected. After performing several interrupt events, an average flow spike waveform may be calculated. Those flow waveforms that deviate more than a certain percentage from the average waveform and do not meet the repeatability criteria can be excluded from further analysis.

As one of the possible options, airway resistance may be determined for each single interruption event. The mean airway resistance may then be calculated during the performance of the plurality of interruption events. Alternatively, the average post-occlusion flow waveform may be calculated with the exclusion of a single interruption event that does not meet repeatability criteria. Airway resistance may then be calculated from the mean flow waveform.

The measurement procedure may be automatically completed if the required number of acceptable interrupt events is generated and measured.

The shutter may be made of a thin plastic or metal material, and therefore is fragile if knocked open and struck by foreign objects. In fig. 8 and 9, a guard ring is shown added at the end of the flow tube, which can be used to prevent the shutter from being knocked due to inadvertent storage. The guard ring is arranged so as not to significantly interfere with the movement of the shutter or the air flow exiting the flow tube. While a ring has been illustrated, it should be appreciated that the shutter guard may take different forms, for example it may comprise a plurality of protrusions arranged around the distal end of the flow tube. This alternative arrangement may provide lower interference with the airflow at the distal end of the flow tube. The shutter guard may be further designed to protect the shutter in its closed and open positions.