WO2011001346A1

WO2011001346A1 - A cardiopulmonary resuscitation (cpr) feedback system

Info

Publication number: WO2011001346A1
Application number: PCT/IB2010/052906
Authority: WO
Inventors: Haris Duric; Pierre Hermanus Woerlee
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2009-07-03
Filing date: 2010-06-25
Publication date: 2011-01-06
Anticipated expiration: 2012-01-03

Abstract

A cardiopulmonary resuscitation (CPR) feedback system comprises a sensor and area measuring unit. The sensor surrounds a patient's thorax for obtaining a measurement indicative of the cross-sectional area of the sensor and therefore the cross-sectional area of the patient's thorax. The area measuring unit utilizes the measurement to determine a change in the cross-sectional area of the sensor to determine the thoracic cross-sectional area change during CPR. The sensor comprises a deformable coil (201) surrounding the patient's thorax. The cross sectional area of the sensor A of the coil is proportional to the magnitude of the self-inductance of the coil. Alternative sensors are an elastic belt incorporating a strain-gauge, a capacitive belt or a resistive belt.

Description

A cardiopulmonary resuscitation (CPR) feedback system

FIELD OF THE INVENTION

The present invention relates to a cardiopulmonary resuscitation (CPR) feedback system, and further to a method of applying CPR to a patient. BACKGROUND OF THE INVENTION

CPR, or cardiopulmonary resuscitation, is a technique designed to temporarily circulate oxygenated blood through the body of a person whose heart has stopped beating or has an irregular rhythm. It involves determining if the person is without a pulse, assessing the airway, applying pressure to the chest to circulate blood to the body's vital organs and ventilating the person's lungs. CPR also helps pre-condition the heart to receive a

defibrillation shock by perfusing it with blood. It is critical for emergency medical responders to perform CPR quickly and effectively to maximize the victim's chances of survival.

However, performing and sustaining the appropriate amount of chest compressions and ventilations is difficult, further complicated by factors such as a chaotic environment or fatigue.

Sudden Cardiac Arrest affects 340,000 people each year in the U.S. alone, and fewer than five percent survive, largely because defibrillators do not get to them in time or CPR was not performed. For each minute that passes before CPR and defibrillation, the chance for survival decreases by about 7 to 10 percent. After 10 minutes, few attempts of resuscitation are successful. Early CPR and defibrillation together with good post- resuscitation care can improve survival rates substantially.

Recent studies published in Journal of the American Medical Association revealed that, in many cases CPR performed by medical professionals in and out of the hospital does not meet the guidelines. In the majority of studied cases the chest compression rates were too low, depth too shallow, and ventilation rates too high.

Direct cardiac compressions and intrathoracic pressure build-up are the primary causes of generated blood flow during CPR. A real-time feedback of the

compression depth can help improve the quality of the applied compressions, but today the compression depth is measured in a direction perpendicular to the sternum and has only one- dimensional relation to the intrathoracic pressure. This results in that the CPR devices that are being used today are prone to errors and adverse patient outcome by measuring the traveled distance of the compression, which include not only the compression of the thoracic but also the compression of the mattress the patient is lying on as well. As a result the compression depth may be overestimated by the state-of-the-art devices whereas the actual compression depth is insufficient.

SUMMARY DESCRIPTION OF THE INVENTION

The object of the present invention is to overcome the above mentioned drawbacks by improving the quality and control of manual and automated CPR system.

According to a first aspect the present invention relates to a cardiopulmonary resuscitation (CPR) feedback system, comprising:

a sensor adapted to be attached around a patient's thorax for measuring the cross-sectional area of the sensor when attached around a patient's thorax, the measured cross-sectional area being indicative to a thoracic cross-sectional area of the patient,

an area measuring unit adapted to utilize said measured cross-sectional area to determine a change in the cross-sectional area of the sensor, the determined cross-sectional area change of the sensor being used to determine the actual thoracic cross-sectional area change of the patient when a cardiac compression is performed on the patient.

Accordingly, by monitoring the cross-sectional area change instead of said traveled distance of the compression said error due to the compression of the mattress the patient is lying on is eliminated. It follows that the chest compression can be accurately determined and thus it is possible to improve significantly the quality and control of manual and automated CPR.

In one embodiment, the sensor is a deformable coil which is adapted to be attached around the patient's thorax, said thoracic cross-sectional area of the sensor being the cross-sectional area A of the coil and is reflected in the self- inductance of the coil which magnitude is proportional to the cross-sectional area A of the coil.

In one embodiment, the sensor is selected from:

- an elastic belt incorporating a strain-gauge, said thoracic cross-sectional area being reflected in the force on the strain gauge, or

a capacitive belt, said thoracic cross-sectional area being reflected in the capacitance value of the capacitive belt, or a resistive belt, said thoracic cross-sectional area being reflected in the resistance value of the resistive belt.

In one embodiment, the CPR feedback system further comprises an audio and/or visual feedback unit adapted to be coupled to a processor, the processor further being adapted to use the thoracic cross-sectional area change of the thorax to determine frequency and volume of compressions or ventilations, the audio and/or visual feedback unit being adapted for providing audio and/or visual feedback indicative of the frequency and the volume of compressions or ventilations. In that way, it is possible to provide e.g. emergency medical responder about the frequency and volume of both the compression and ventilation phase. Thus, the CPR feedback system is capable of measuring area change and is thus suited for both phases of CPR procedure. Typically, first around 30 chest compressions are performed (frequency 90/min) followed by 2 ventilations. During ventilation the chest expands, which is detected by the CPR feedback system, and an indication of ventilation air volume can thus be calculated.

In one embodiment, the sensor includes multiple sensors coupled together and arranged along the longitudinal axis of the patient's thorax are used for measuring the cross- sectional area of the sensors when attached around a patient's thorax. Thus, a spatial resolution along the longitudinal axis of the patient is obtained, which improves the efficiency of the chest compression further.

In one embodiment, the cross-sectional area change is further utilized to estimate the lung inflation during the ventilation phase.

According to another aspect, the present invention relates to a kit for a cardiopulmonary resuscitation (CPR) feedback system, comprising:

an area measuring unit adapted to be coupled to the sensor for utilizing said measured cross-sectional area to determine a change in the cross-sectional area of the sensor, the determined cross-sectional area change of the sensor being used to determine the actual thoracic cross-sectional area change of the patient when a cardiac compression is performed on the patient.

In one embodiment, the kit further comprises an audio and/or visual feedback unit adapted to be coupled to a processor, the processor further being adapted to use the thoracic cross-sectional area change of the patient to determine frequency and volume of compressions or ventilations of the thorax, the audio and/or visual feedback unit being adapted for providing audio and/or visual feedback indicative of the frequency and the volume of compressions or ventilations.

According to still another aspect, the present invention relates to a method of applying cardiopulmonary resuscitation (CPR), comprising:

placing a sensor around a patient's thorax for measuring the cross-sectional area of the sensor when attached around a patient's thorax, the measured cross-sectional area being indicative to a thoracic cross-sectional area of the patient,

utilizing said measured cross-sectional area to determine a change in the cross- sectional area of the sensor, the determined cross-sectional area change of the sensor being used to determine the actual thoracic cross-sectional area change of the patient when a cardiac compression is performed on the patient.

According to yet another aspect, the present invention relates to a computer program product for instructing a processing unit to execute the said method steps when the product is run on a computer.

The aspects of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

Fig. 1 shows an embodiment of a cardiopulmonary resuscitation (CPR) feedback system according to the present invention comprising a sensor and an area measuring unit,

Fig. 2 depicts graphically a coil with variable surface-area that is attached around the patient's thorax, and

Fig. 3 shows an embodiment of a method according to the present invention of applying cardiopulmonary resuscitation (CPR).

DESCRIPTION OF EMBODIMENTS

Figure 1 shows an embodiment of a cardiopulmonary resuscitation (CPR) feedback system 100 according to the present invention comprising a sensor (S) 101 and an area measuring unit (A_M_U) 102. In one embodiment, the sensor (S) 101 is a deformable coil which is adapted to be attached around the patient's thorax, where the thoracic cross-sectional area of the sensor is the cross-sectional area A of the coil (or in general, a solenoid). The area variation is reflected in the self- inductance L of the coil, which magnitude is directly proportional to the cross-sectional area A, as given by the Eq.1, μ₀μ_rN²A

L = Eq.1.

N is the number of windings, / the length of the coil, μ₀ is the vacuum permeability, and μ_x is the relative permeability of the material within the area A, i.e. the patient's thorax, but μ_x can be estimated relative accurately by assuming the permeability of water, but the underlying tissue composition remains substantially constant during the procedure and has thus negligible effect on the measurement.

Preferably, a deformable coil with elastic properties is applied to closely follow the chest circumference of the patient. In this case a surface-integral related to chest deformation is measured rather than one-dimensional displacement at the point of applied pressure.

The sensor (S) 101 is not limited to such a deformable coil. Other types of sensors are also possible, including and not limited to: an elastic belt incorporating a strain- gauge, where the thoracic cross-sectional area is reflected in the force on the strain gauge, a capacitive belt, where the thoracic cross-sectional area is reflected in the capacitance value of the capacitive belt, or a resistive belt where the thoracic cross-sectional area is reflected in the resistance value of the resistive belt.

The area measuring (A M U) unit 102 is adapted to utilize the measured cross-sectional area to determine a change in the cross-sectional area of the sensor, but this determined cross-sectional area change of the sensor is used to determine the actual thoracic cross-sectional area change of the patient when a cardiac compression is performed on the patient (see Figure. 2). The area measuring (A M U) unit 102 may comprise or be coupled to a processor (P) 103 that repeatedly calculates A in Eq. 1, and thus how A changes between e.g. two subsequent time points. Also calibration parameters that are collected empirically by measurements can be stored in the processing unit and retrieved to perform the calculations.

In this embodiment, the CPR feedback system 100 further comprises an audio and/or visual feedback unit (A/V F U) 104 that is adapted to be coupled to the processor (P) 103, which uses the thoracic cross-sectional area change of the patient to determine frequency and volume during the compression and ventilation phase. The audio and/or visual feedback unit is further adapted for providing audio and/or visual feedback indicative of the frequency and the volume of ventilations, such as to an emergency medical responder. Thus, during the ventilation phase of the CPR it is possible to monitor the respiratory activity and provide feedback to the emergency medical responder about the volume of ventilations. It is namely so that when non well-trained people are performing resuscitation it may happen that the airway is not opened properly and thus no air flows into the lungs during the ventilation phase. Therefore, by monitoring chest expansion an indication of the air- flow to the lungs can be provided.

The ventilation phase can be automatically detected by sensing chest expansions instead of compressions, or can be manually selected in order to simplify adaptation to the smaller dynamic range of breathing. This audio and/or visual feedback can be in the form of a sound via speech commands where the user is informed about the status and various parameters and how the compression should be performed, or by displaying certain colors or waveforms or by displaying status information on a display screen.

The frequency of compressions of the thorax may as an example be determined based on the dividing a given number of compressions with the time needed to perform these compressions. As an example, if 10 compressions took 20 seconds the frequency would be 10/20SeC=O^s^"1. If the frequency of 90 compressions per minute

(90/60SeC=LSs^"1) would be required, a feedback could be given to the medical emergency responder to compress (three times) faster.

Further, during the ventilation phase the volume of the thorax may be determined or approximated by e.g. assuming elliptical-cylindrical volume scaled to the patient size, or using pre-determined parameters that are based on observations from previous victims, or applying a calibration step for an individual victim. In this manner an indication of the ventilation effectiveness could be assessed. In many CPR cases not well-trained personnel may fail to clear the airway sufficiently and subsequently no air will enter the lungs. In such case feedback and/or instructions could be provided to the medical emergency responder to correct for this.

The CPR system can be a manual system, semi-manual system or fully automated. In case the system is fully automated the output of the area measuring (A M U) unit 102 may be fed to the processor (P) 103 which regulates such parameters as compression area, compression rate and compression pulse waveform (e.g. duty cycle) in order to optimize the pressure profile for maximum blood flow.

In one embodiment, a strap or similar means comprising multiple coils arranged substantially in parallel is used to obtain cross-sectional measurements at a multitude of locations along the spinal cord, but the additional spatial information may be used to enhance the interpretation in determining the change in the thoracic cross-sectional area. Accordingly, multiple cross sectional area changes of the thoracic are obtained which give more accurate results of the actual volume of the thorax.

Figure 2 depicts graphically a coil 201 with variable surface-area that is attached around the patient's thorax. As shown, during the chest compressions as indicated by the arrow 202 the cross-sectional area A 203 of the thorax varies. Today's real time CPR feedback systems are based on determining compression depth (e.g. based on accelerometer reading) by measuring the compression in a direction as indicated by the arrow 202 perpendicular to the sternum and thus has only one-dimensional relation to the intrathoracic pressure. This has the consequences that if the patient is lying on a soft compressible material such as a mattress, the mattress also becomes compressed during the compression and therefore the compression depth is not only the compression due to the compression of the thorax but also based on the compression caused by the mattress. Thus, the traveled distance of the compression consists of the compression of the thorax and the compression of the mattress.

Accordingly, by implementing said cross-sectional area change instead it is possibly to provide a real-time and reliable feedback of thoracic cross-sectional area (and volume) variation of the chest.

Figure 3 shows an embodiment of a method according to the present invention of applying cardiopulmonary resuscitation (CPR).

In a first step (Sl) 301, a sensor is placed around a patient's thorax for measuring the cross-sectional area of the sensor when attached around a patient's thorax, where the measured cross-sectional area being indicative to a thoracic cross-sectional area of the patient. As mentioned previously in relation to Figure. 1, the sensor can be a deformable coil, an elastic belt incorporating a strain-gauge, were the thoracic cross-sectional area is reflected in the force on the strain gauge, a capacitive belt, where the thoracic cross-sectional area is reflected in the capacitance value of the capacitive belt, or resistive belt where the thoracic cross-sectional area is reflected in the resistance value of the resistive belt. In a second step (S2) 303, the determined cross-sectional area change of the sensor is used to determine the actual thoracic cross-sectional area change of the patient when a cardiac compression is performed on the patient. Accordingly, the change could be based on the difference between two subsequent determined cross-sectional areas, e.g.

etc, it follows that AA_ι→2 = -5 cm², ΔA_2→3 = -2 cm² etc. These area changes can easily be converted into thoracic volume changes by e.g. assuming electrical-cylindrical volume which would preferably be scaled to the patient size. An emergency medical responder or a regular user could thus enter the height of the person and eventually additional information such as age, weight etc, before applying CPR. In that way, these input data could be used as additional data used to scale the area changes correctly to volume changes.

Certain specific details of the disclosed embodiment are set forth for purposes of explanation rather than limitation, so as to provide a clear and thorough understanding of the present invention. However, it should be understood by those skilled in this art, that the present invention might be practiced in other embodiments that do not conform exactly to the details set forth herein, without departing significantly from the spirit and scope of this disclosure. Further, in this context, and for the purposes of brevity and clarity, detailed descriptions of well-known apparatuses, circuits and methodologies have been omitted so as to avoid unnecessary detail and possible confusion.

Reference signs are included in the claims, however the inclusion of the reference signs is only for clarity reasons and should not be construed as limiting the scope of the claims.

Claims

CLAIMS:

1. A cardiopulmonary resuscitation (CPR) feedback system (100), comprising:

a sensor (101) adapted to be attached around a patient's thorax for measuring the cross-sectional area of the sensor when attached around a patient's thorax, the measured cross-sectional area being indicative to a thoracic cross-sectional area of the patient,

- an area measuring unit (102) adapted to utilize said measured cross-sectional area to determine a change in the cross-sectional area of the sensor, the determined cross- sectional area change of the sensor being used to determine the actual thoracic cross-sectional area change of the patient when a cardiac compression is performed on the patient. 2. A CPR feedback system according to claim 1, wherein the sensor is a deformable coil (201) which is adapted to be attached around the patient's thorax, said thoracic cross-sectional area of the sensor being the cross-sectional area A of the coil and is reflected in the self- inductance of the coil which magnitude is proportional to the cross- sectional area A of the coil.

3. A CPR feedback system according to claim 1, wherein the sensor (101) is selected from:

an elastic belt incorporating a strain-gauge, said thoracic cross-sectional area being reflected in the force on the strain gauge, or

- a capacitive belt, said thoracic cross-sectional area being reflected in the capacitance value of the capacitive belt, or

a resistive belt, said thoracic cross-sectional area being reflected in the resistance value of the resistive belt. A. A CPR feedback system according to claim 1, further comprising an audio and/or visual feedback unit (104) adapted to be coupled to a processor (103), the processor further being adapted to use the thoracic cross-sectional area change of the patient to determine frequency and volume of compressions or ventilations of the thorax, the audio and/or visual feedback unit being adapted for providing audio and/or visual feedback indicative of the frequency and the volume of compressions or ventilations.

5. A CPR feedback system according to claim 1, the sensor (101) includes multiple sensors coupled together and arranged along the longitudinal axis of the patient's thorax are used for measuring the cross-sectional area of the sensors when attached around a patient's thorax.

6. A CPR feedback system according to claim 1, wherein the cross-sectional area change is further utilized to estimate the lung inflation during the ventilation phase.

7. A kit for a cardiopulmonary resuscitation (CPR) feedback system (100), comprising:

an area measuring unit (102) adapted to be coupled to the sensor for utilizing said measured cross-sectional area to determine a change in the cross-sectional area of the sensor, the determined cross-sectional area change of the sensor being used to determine the actual thoracic cross-sectional area change of the patient when a cardiac compression is performed on the patient.

8. A kit according to claim 7, further comprising an audio and/or visual feedback unit (104) adapted to be coupled to a processor (103), the processor further being adapted to use the thoracic cross-sectional area change of the patient to determine frequency and volume of compressions or ventilations of the thorax, the audio and/or visual feedback unit being adapted for providing audio and/or visual feedback indicative of the frequency and the volume of compressions or ventilations. 9. A method of applying cardiopulmonary resuscitation (CPR), comprising:

placing a sensor around a patient's thorax for measuring the cross-sectional area of the sensor when attached around a patient's thorax (301), the measured cross- sectional area being indicative to a thoracic cross-sectional area of the patient,

utilizing said measured cross-sectional area to determine a change in the cross- sectional area of the sensor (303), the determined cross-sectional area change of the sensor being used to determine the actual thoracic cross-sectional area change of the patient when a cardiac compression is performed on the patient. 10. A computer program product for instructing a processing unit to execute the method step of claim 9 when the product is run on a computer.