WO2009109903A1

WO2009109903A1 - Device for combined heart rate and respiration measurement with a single sensor

Info

Publication number: WO2009109903A1
Application number: PCT/IB2009/050840
Authority: WO
Inventors: Robert Pinter; Jens Muehlsteff
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N.V.
Priority date: 2008-03-06
Filing date: 2009-03-03
Publication date: 2009-09-11

Abstract

A device for combined heart rate and respiration measurement of a patient. This device comprises a strain gauge (2) providing a strain gauge signal in dependence of detected strain, an elastic carrier (3) for carrying the strain gauge (2), and two stickers (5) for sticking the device on the patient's chest (9). The strain gauge (2) and the stickers 5 are arranged on the elastic carrier (3) in such a way that movements of the patient's chest (9) due to heart beat and/or respiration lead to a varying strain gauge signal. This way, low cost monitoring in the normal ward is provided, capturing the basic vitalsigns pulse and respiration.

Description

DEVICE FOR COMBINED HEART RATE AND RESPIRATION MEASUREMENT WITH A SINGLE SENSOR

FIELD OF THE INVENTION

The invention relates to the field of heart rate and respiration measurement, and especially to a combined measurement with a single sensor. BACKGROUND OF THE INVENTION Pulse and respiration are one of the most important basic vital signs to assess the health status of a patient. In intensive care unit (ICU) settings, pulse and respiration are routinely measured via ECG electrodes from the electrocardiogram, and the measured thorax-impedance changes during breathing activity, respectively. Since patients in an ICU are normally immobile, for monitoring purposes stationary devices decoupled from the patient's body are used, which produce alarms in case of detected unusual parameters.

But interestingly, more patients die not in the ICU but in the normal ward, because of missed detection of a patient degradation. Nowadays, approx. 80 % of cardiac arrests, approx. 50 % of non-DNR deaths and approx. 70% of unexpected ICU admissions occur in the normal ward. Hospitals are aware of these facts and have installed so called Rapid Response Teams (RRT). An RRT is a team of clinicians who bring critical care expertise to the bedside. RRTs have proven to have high effectiveness. Anyway, the missing part today is the early detection of events, which are often preceded by several hours of slow deterioration. In the normal ward, a nurse usually checks a patient's pulse and respiration only twice a day. i.e. in the morning and in the evening, respectively, which does not provide enough information to detect upcoming critical conditions. SUMMARY OF THE INVENTION

It is the object of the invention to provide for low cost comfortable monitoring in the normal ward, capturing the basic vital signs pulse and respiration.

This object is achieved by a device for combined heart rate and respiration measurement of a patient, the device comprising a strain gauge providing a strain gauge signal in dependence of detected strain, an elastic carrier for carrying the strain gauge, and a sticking means for sticking the device on the patient's chest, wherein the strain gauge and the sticking means are arranged on the elastic carrier in such a way that movements of the patient's chest due to heart beat and/or respiration lead to a varying strain gauge signal.

A strain gauge is a device used to measure deformation, i.e. strain of an object. The most common type of strain gauges consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate. As the object is deformed, the foil is deformed, too, causing its electrical resistance to change. This resistance change, preferably measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor.

Thus, the invention employs a single sensor that picks up both cardiac activity in terms of heart rate and respiratory activity in terms of breathing rate. It is easily applicable and can be produced at low costs, thereby allowing an uncomplicated long-term monitoring of cardiac and respiratory activity. Accordingly, the solution according to the invention provides reliable information on the patient's pulse and respiration while ensuring minimal effort for the nurse to apply the device and providing maximal comfort for the patient. Further, such a device can be designed very robust in terms of misuse and shows minimal false alarm rate taking into account the context of a measurement. These are essential features of the invention since ward patients are very mobile and not fixed to the bed, and, thus, reliability in multiple different measurement situations is very important.

According to a preferred embodiment of the invention, the sticking means comprises two stickers for sticking the device on the patient's chest. Further, it is possible to provide more than two stickers, i.e. three stickers, wherein the third sticker is arranged in the middle between the first and the second sticker. This way, the device can be arranged on the patient's chest in such a way that the third sticker in the middle is attached on the breast bone.

Generally, different types of carriers can be used for the device. However, according to the preferred embodiment of the invention, the elastic carrier is a semi- elastic carrier. This means that the carrier comprises such an elasticity which is sufficient in order not to hinder the bending while not being too soft in order to give shape to the whole device.

Further, the strain gauge can be arranged in different ways on the elastic carrier. However, according to a preferred embodiment of the invention, the strain gauge is arranged between the stickers. With respect to this, it is most preferred that the strain gauge is arranged in the middle between the stickers. This way, movements of the chest due to the heart beat or due to respiration can be detected in a most reliable way.

In general, it is possible to detect and process the direct signal originating from the strain gauge in order to monitor heart beat and respiration. However, according to a preferred embodiment of the invention, the strain gauge is provided in a Wheatstone bridge configuration. A Wheatstone bridge usually comprises four resistors. If the strain gauge is provided as one of the resistors, in general, the other resistors can be constant. However, according to a further preferred embodiment of the invention, four strain gauges are provided in the Wheatstone bridge. This provides for a higher sensitivity of the setup.

Further, according to a preferred embodiment of the invention, a first strain gauge and a second strain gauge are attached to one side of a carrier board and a third strain gauge and a fourth strain gauge are attached to the other side of the carrier board, wherein the strain gauges are connected in such a way that if the carrier board is bent into one direction the first strain gauge and the third strain gauge increase their values and the second strain gauge and the fourth strain gauge decrease their value and vice versa. This carrier board can be identical to the elastic carrier of the device or it can be an additional device mounted on the elastic carrier. Generally, the stickers can be connected to the device in a non-detachable fashion. However, according to the invention, the stickers are detachable from the device. This is advantageous since this way, the elastic carrier together with the strain gauge can be designed for re-use while the stickers can be disposable. With respect to this, according to a preferred embodiment of the invention, the carrier is provided with two fittings, especially made of metal or plastics, for attaching standard ECG electrodes as stickers. This way, no special stickers are necessary and, thus, the device is widely deployable without requiring special accessories.

Further, according to a preferred embodiment of the invention, a signal processing unit is provided which is adapted for processing the strain gauge signal and for separating the signal components which result from the heartbeat from those signal components which result from respiration. Furthermore, it is preferred that the device also comprises an accelerometer for providing an accelerometer signal. Especially, this accelerometer signal is used for context information on the patient's movements.

If, for example, disturbances in the strain gauge signal are detected, that could indicate a serious health condition, first, the acceleration information is checked. If there is no movement or only little movement present, a motion artefact can be excluded, and an alarm condition is issued. The accelerometer also allows for general activity monitoring and posture classification of the patient.

If positioned in a suitable position, the accelerometer can even provide information on the heaving of the chest due to respiration. Thereby, the respiratory information as extracted from the strain gauge signal can be verified.

According to a preferred embodiment of the invention, the device is battery-powered Further, it is preferred that the device contains a wireless link in order to transmit the measured parameters to a base station. BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the drawings:

Fig. Ia and b show a device for combined heart rate and respiration measurement of a patient according to a preferred embodiment of the invention with stickers detached and attached to the device, respectively, Fig. 2a and b schematically show the application of the device for combined heart rate and respiration measurement of a patient according to the preferred embodiment of the invention, Fig. 3 schematically shows the arrangement of four strain gauges on top and on the bottom of a carrier board, respectively, Fig. 4 schematically shows the four strain gauges in a

Wheatstone bridge configuration, and

Fig. 5 shows a block diagram of the electronics unit of the device for combined heart rate and respiration measurement of a patient according to the preferred embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS Fig. Ia and b illustrate a device for combined heart rate and respiration measurement of a patient according to a preferred embodiment of the invention. This device comprises a strain gauge sensor 1 with multiple strain gauges 2 which provides a strain gauge signal in dependence of detected strain. The strain gauge sensor 1 is embedded into a semi-elastic carrier 3 that is provided with two fittings 4 into which stickers 5 like standard ECG electrodes or other disposable stickers can be inserted. The strain gauge sensor 1 and the stickers 5 are arranged on the elastic carrier in such a way that movements of the patient's chest 9 due to heart beat and/or respiration lead to a varying strain gauge signal. This is shown in Figs. 2a and 2b. Though these Figures show the device in a vertical arrangement, the device can be used in a horizontal arrangement or another arrangement, too.

The fittings 4 are preferably made of metal so that they provide a good mechanical fixation. Further, an electronics unit 6 is provided which comprises a suitable circuitry for conditioning the strain gauge sensor signal, i.e. a constant voltage source 7 and a differential amplifier 8 as can be seen from Fig. 5. The semi-elastic mechanical carrier 3 is a printed circuit board according to the preferred embodiment of the invention. As can be seen from Figs. 3 and 4, respectively, according to the preferred embodiment of the invention, the strain gauge sensor 1 comprises four strain gauges 2, i.e. two strain gauges 2 on top and two strain gauges 2 on the bottom of the elastic carrier 3 are combined in order to form a Wheatstone bridge configuration 10. In > the Wheatstone bridge, the bridge voltage Ub is given by u_h =u. ^V3

R_v +R₂ R₃ +R₄

U_s is a constant voltage source, i.e. the measured bridge voltage Ub changes with the mechanical deformation of the strain gauges 2 in the Wheatstone bridge 10. Just a single strain gauge 2 could be used as a sensor in such a configuration, and the other resistors could be kept constant, but in order to maximize the sensitivity of the setup, all four resistors in the Wheatstone bridge are strain gauges 2.

As already stated above, two of the four strain gauges 2 are mounted on top of the carrier 3, and the other two strain gauges 2 are mounted on the bottom of the carrier 3. They are connected in such a way that if the carrier 3 is bent into one direction, the strain gauges 2 which are marked with Rl and R4 increase their values, while the strain gauges 2 which are marked with R2 and R3 decrease their values. If the carrier 3 is bent into the other direction, the strain gauges 2 marked with Rl and R4 decrease their values, while the strain gauges 2 which are marked with R2 and R3 increase their values. According to the preferred embodiment of the invention, a 3D accelerometer 11 is integrated into the device. This has the advantage that context information on the patient's movements becomes available. If, for example, disturbances in the strain gauge signal are detected, that could indicate a serious health condition, a microcontroller 12 which is fed with the signal from the Wheatstone bridge and with the 3D acceleration signal via an A/D converter 14 will first check the acceleration information. If there is no movement or only little movement present, a motion artefact can be excluded, and the microcontroller 12 will issue an alarm condition. The accelerometer 11 also allows for general activity monitoring and posture classification of the patient. If positioned in a suitable position, the accelerometer 11 can even provide information on the heaving of the chest due to respiration. Thereby, the respiratory information as extracted from the strain sensor signal can be verified. A block-diagram of the electronics unit 6 can be seen from Fig. 5. As can be seen from this block-diagram, the device further comprises a wireless link 13 for connecting with a remote base station. The invention is preferably applied in long-term monitoring of cardiac and respiratory activity in a clinical setting, in long-term monitoring of cardiac and respiratory activity in a home setting (personal healthcare), in disease management of patients suffering from chronic heart disease, in syncope diagnostics, and in fall prevention devices. While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

Other variations to the disclosed embodiments can be understood and effected 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 indefinite article "a" or "an" does 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 measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A device for combined heart rate and respiration measurement of a patient, the device comprising a strain gauge (2) providing a strain gauge signal in dependence of detected strain, an elastic carrier (3) for carrying the strain gauge (2), and a sticking means for sticking the device on the patient's chest (9), wherein the strain gauge (2) and the sticking means are arranged on the elastic carrier (3) in such a way that movements of the patient's chest (9) due to heart beat and/or respiration lead to a varying strain gauge signal.

2. The device according to claim 1, wherein the sticking means comprises two stickers (5) for sticking the device on the patient's chest (9).

3. The device according to claim 2, wherein the strain gauge (2) is arranged between the stickers (5).

4. The device according to any of claims 1 to 3, wherein the strain gauge (2) is provided in a Wheatstone bridge configuration (10).

5. The device according to claim 4, wherein four strain gauges (2) are provided which are arranged in the Wheatstone bridge configuration (10).

6. The device according to claim 5, wherein a first strain gauge (2) and a second strain gauge (2) are attached to one side of a carrier board and a third strain gauge (2) and a fourth strain gauge (2) are attached to the other side of the carrier board and wherein the strain gauges (2) are connected in such a way that if the carrier board is bent into one direction the first strain gauge (2) and the third strain gauge (2) increase their values and the second strain gauge (2) and the fourth strain gauge (2) decrease their value, and vice versa.

7. The device according to any of claims 1 to 6, wherein the sticking means is detachable from the device.

8. The device according to claim 7, wherein the carrier (3) is provided with two fittings (4) for attaching stickers (5), especially for attaching standard ECG electrodes.

9. The device according to any of claims 1 to 8, wherein a signal processing unit (6) is provided for processing the strain gauge signal and for separating the signal components which result from the heartbeat from those signal components which result from respiration.

10. The device according to any of claims 1 to 9, wherein the device comprises an accelerometer (11) for providing an accelerometer signal.

11. The device according to claim 10, wherein the accelerometer signal is used for context information on the patient's movements.