DETERMINATION OF CARDIOPULMONARY RESUSCITATION COMPRESSION RATE

Abstract

A defibrillator for determining a cardiopulmonary resuscitation (CPR) compression rate, including electrodes adapted to be attached to the subject, an impedance signal measurement system connected to the electrodes and configured to measure at least one impedance signal of the subject, an electrocardiogram signal measurement system connected to the electrodes, an impedance signal processing system connected to the impedance signal measurement system, an electrocardiogram signal processing system connected to the electrocardiogram signal measurement system, a compression rate estimate processing system configured to apply a plurality of criteria to the impedance signal features and the electrocardiogram signal features and use compliance with one or more of the criteria to select one of the plurality of impedance signal compression rate estimates as the cardiopulmonary resuscitation compression rate, and an output unit configured to output feedback based on the cardiopulmonary resuscitation compression rate to a user of the defibrillator.

Claims

1. A defibrillator for determining a rate of cardiopulmonary resuscitation compressions on a subject, comprising: electrodes adapted to be attached to the subject; an impedance signal measurement system connected to the electrodes and configured to measure at least one impedance signal of the subject to yield a measured impedance signal; an electrocardiogram signal measurement system connected to the electrodes and configured to measure an electrocardiogram signal of the subject to yield a measured electrocardiogram signal; an impedance signal processing system connected to the impedance signal measurement system and configured to process the measured impedance signal of the subject to obtain a plurality of impedance signal compression rate estimates and a plurality of impedance signal features; an electrocardiogram signal processing system connected to the electrocardiogram signal measurement system and configured to process the measured electrocardiogram signal of the subject to obtain a plurality of electrocardiogram signal features; a compression rate estimate processing system connected to the impedance signal measurement system and the electrocardiogram signal measurement system and configured to apply a plurality of criteria to the impedance signal features and the electrocardiogram signal features and use compliance with one or more of the criteria to select one of a plurality of impedance signal compression rate estimates as the rate of cardiopulmonary resuscitation compressions; and an output unit connected to the compression rate estimate processing system and configured to output feedback based on the rate of cardiopulmonary resuscitation compressions to a user of the defibrillator.

2. A defibrillator according to claim 1, in which the impedance signal processing system processes the measured impedance signal to obtain the plurality of impedance signal compression rate estimates by: using a frequency domain transformation on the measured impedance signal to obtain an impedance signal frequency spectrum; using a peak detection algorithm to identify a plurality of peaks in the impedance signal frequency spectrum; and determining central frequencies of the plurality of peaks as the plurality of impedance signal compression rate estimates.

3. A defibrillator according to claim 1, in which the impedance signal processing system processes the measured impedance signal to obtain the plurality of impedance signal features by: using a frequency domain transformation on the measured impedance signal to obtain an impedance signal frequency spectrum; using a peak detection algorithm to identify a plurality of peaks in the impedance signal frequency spectrum; and determining central frequencies and amplitudes of the plurality of peaks as the plurality of impedance signal features.

4. A defibrillator according to claim 1, in which the electrocardiogram signal processing system processes the measured electrocardiogram signal to obtain the plurality of electrocardiogram signal features by: using a frequency domain transformation on the measured electrocardiogram signal to obtain an electrocardiogram signal frequency spectrum; using a peak detection algorithm to identify a plurality of peaks in the measured electrocardiogram signal frequency spectrum; and determining central frequencies and amplitudes of the plurality of peaks as the plurality of electrocardiogram signal features.

5. A defibrillator according to claim 2, in which using the frequency domain transformation to obtain the impedance signal frequency spectrum and the electrocardiogram signal frequency spectrum comprises using any of a Fast Fourier Transform algorithm on a window of the measured impedance signal and a corresponding window of the measured electrocardiogram signal, a Goertzel algorithm on a window of the measured impedance signal and a corresponding window of the measured electrocardiogram signal.

6. A defibrillator according to claim 2, in which using the peak detection algorithm to identify a plurality of peaks in the impedance signal frequency spectrum comprises: identifying peaks based on decreasing steepness of slopes of the impedance signal frequency spectrum; and using the peak detection algorithm to identify a plurality of peaks in the electrocardiogram signal frequency spectrum; and identifying peaks based on decreasing steepness of slopes of the electrocardiogram signal frequency spectrum.

7. A defibrillator according to claim 6, in which the peak detection algorithm returns a primary peak having a highest amplitude at its central frequency, a secondary peak having a next highest amplitude at its central frequency continued up to a specified number of peaks.

8. A defibrillator according to claim 1, in which the impedance signal processing system processes the measured impedance signal to obtain a plurality of additional impedance signal features from the measured impedance signal comprising any of variance of the impedance signal, a morphology of the impedance signal, a gradient of the measured impedance signal, a power of the measured impedance signal, wavelet decomposition of the measured impedance signal, a noise analysis of the measured impedance signal, and a cepstrum of the measured impedance signal.

9. A defibrillator according to claim 1, in which the electrocardiogram signal processing system processes the measured electrocardiogram signal to obtain a plurality of additional electrocardiogram signal features from the electrocardiogram signal comprising any of a variance of the electrocardiogram signal, a morphology of the electrocardiogram signal, a gradient of the electrocardiogram signal, a power of the electrocardiogram signal, a wavelet decomposition of the measured electrocardiogram signal, a noise analysis of the measured electrocardiogram signal, and a cepstrum of the measured electrocardiogram signal.

10. A defibrillator according to claim 1, in which the plurality of criteria applied by the compression rate estimate processing system comprises a criterion comprising in an impedance signal frequency spectrum a ratio of a secondary peak amplitude and a primary peak amplitude being greater than a pre-determined impedance signal amplitude ratio threshold.

11. A defibrillator according to claim 1, in which the plurality of criteria applied by the compression rate estimate processing system comprises a criterion comprising in an impedance signal frequency spectrum a central frequency of a primary peak being greater than a central frequency of a secondary peak.

12. A defibrillator according to claim 1, in which the plurality of criteria applied by the compression rate estimate processing system comprises a criterion comprising in the electrocardiogram signal frequency spectrum a central frequency of a primary peak being less than a central frequency of a secondary peak.

13. A defibrillator according to claim 1, in which the plurality of criteria applied by the compression rate estimate processing system comprises a criterion comprising a frequency difference between a lower frequency primary or secondary peak in an impedance signal frequency spectrum and a lower frequency primary or secondary peak in the electrocardiogram signal frequency spectrum being less than a pre-determined frequency difference threshold.

14. A defibrillator according to claim 1, in which the compression rate estimate processing system uses compliance with one or more of the plurality of criteria to select an impedance signal compression rate estimate as a CPR compression rate.

15. A defibrillator according to claim 1, in which the compression rate estimate processing system uses compliance with each of the plurality of criteria to select an impedance signal compression rate estimate comprising a central frequency of a secondary peak of an impedance signal frequency spectrum as a CPR compression rate.

16. A defibrillator according to claim 1, in which the compression rate estimate processing system uses non-compliance with any of the plurality of criteria to select an impedance signal compression rate estimate comprising a central frequency of a primary peak of an impedance signal frequency spectrum as a CPR compression rate.

17. A defibrillator according to claim 1, in which the plurality of criteria applied by the compression rate estimate processing system comprises a criterion comprising in the electrocardiogram signal frequency spectrum a ratio of a secondary peak amplitude and a primary peak amplitude being greater than a pre-determined electrocardiogram signal amplitude ratio threshold.

18. A defibrillator according to claim 17, in which the compression rate estimate processing system uses compliance with each of the plurality of criteria to select an impedance signal compression rate estimate comprising a central frequency of a secondary peak of an impedance signal frequency spectrum as a CPR compression rate.

19. A defibrillator according to claim 17, in which the compression rate estimate processing system uses non-compliance with any of the plurality of criteria to select an impedance signal compression rate estimate comprising a central frequency of a primary peak of the impedance signal frequency spectrum as a CPR compression rate.

20. A defibrillator according to claim 1, which uses substantially all of the measured impedance signal and substantially all of the measured electrocardiogram signal to determine a CPR compression rate.

21. A defibrillator according to claim 1, which uses one or more portions of the measured impedance signal and corresponding one or more portions of the measured electrocardiogram signal to determine a CPR compression rate.

22. A defibrillator according to claim 21, in which each portion of the measured impedance signal comprises portions which have been pre-analysed for CPR compression rate, which compression rate has not exceeded a threshold used to determine if a rate is a true rate.

23. A defibrillator according to claim 1, in which the output unit outputs feedback based on a CPR compression rate to the user of the defibrillator comprising an indication that the CPR compression rate is any of satisfactory, too slow, too fast.

24. A method of determining a cardiopulmonary resuscitation (CPR) compression rate, the method comprising: receiving an impedance signal of a subject; receiving an electrocardiogram signal of the subject; processing the impedance signal to obtain a plurality of impedance signal compression rate estimates; processing the impedance signal to obtain a plurality of impedance signal features; processing the electrocardiogram signal to obtain a plurality of electrocardiogram signal features; and applying a plurality of criteria to the impedance signal features and the electrocardiogram signal features and using compliance or non-compliance with one or more of the criteria to select one of the plurality of impedance signal compression rate estimates as the CPR compression rate.

25. A computer-readable storage device, having instructions for controlling a processor, wherein, when executed by the processor, causes the processor to perform operations comprising: receiving an impedance signal of a subject; receiving an electrocardiogram signal of the subject; processing the impedance signal to obtain a plurality of impedance signal compression rate estimates; processing the impedance signal to obtain a plurality of impedance signal features; processing the electrocardiogram signal to obtain a plurality of electrocardiogram signal features; and applying a plurality of criteria to the impedance signal features and the electrocardiogram signal features and using compliance or non-compliance with one or more of the criteria to select one of the plurality of impedance signal compression rate estimates as the CPR compression rate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to describe the manner in which the above-recited and other advantages and features of the disclosure can be obtained, a more particular description of the disclosure briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only exemplary embodiments of the disclosure and are not therefore to be considered to be limiting of its scope, the disclosure will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0033] FIG. 1 is a schematic representation of a defibrillator for determining a rate of CPR compressions on a subject according to the first aspect of the disclosure;

[0034] FIG. 2 is a flow chart representation of a method of determining a CPR compression rate carried out by the defibrillator of FIG. 1; and

[0035] FIG. 3 is flow chart representation showing further details of the method of FIG. 2.

DETAILED DESCRIPTION

[0036] Referring to FIG. 1, a defibrillator 1 for determining a rate of CPR compressions on a subject is shown. This includes electrodes 32 adapted to be attached to the subject (not shown), an impedance signal measurement system 5 connected to the electrodes 3 and an ECG signal measurement system 7 connected to the electrodes 3. The defibrillator 1 further includes an impedance signal processing system 9 connected to the impedance signal measurement system 5, an ECG signal processing system 11 connected to the ECG signal measurement system 7, a compression rate estimate processing system 13 connected to the impedance signal processing system 9 and the ECG signal processing system 11 and an output unit 15 connected to the compression rate estimate processing system 13.

[0037] It will be appreciated that the defibrillator 1 will include other elements such as defibrillation shock generation circuitry, a power source.

[0038] The impedance signal measurement system 5 includes an impedance measurement signal generator (not shown) configured to generate an ac signal at a pre-determined voltage and an impedance measurement signal processor (not shown) including at least an amplifier module and a signal conditioning module (not shown). The impedance measurement signal generator generates the ac signal which is sent to the electrodes 3 and passes through the subject. The electrodes 3 produce impedance data indicative of the impedance of the subject which is passed to the impedance measurement signal processor. The impedance measurement signal processor continuously samples the impedance-indicative data received from the electrodes 3. The amplifier module and the signal conditioning module of the impedance measurement signal processor process the impedance data received from the electrodes 3 by any of amplification, filtering, analogue to digital conversion and signal processing. The impedance signal measurement system 5 thus measures at least one impedance signal of the subject which is passed to the impedance signal processing system 9.

[0039] The ECG signal measurement system 7 includes an ECG measurement signal processor (not shown). When placed on the subject, the electrodes 3 produce ECG data indicative of the ECG of the subject which is passed to the ECG measurement signal processor. The ECG measurement signal processor continuously samples the ECG-indicative data received from the electrodes 3 and then processes the ECG data received from the electrodes 3. The ECG signal measurement system 7 thus measures at least one ECG signal of the subject which is passed to the ECG signal processing system 11.

[0040] The impedance signal processing system 9 includes at least one micro processor which processes the impedance signal to obtain a plurality of impedance signal compression rate estimates and a plurality of impedance signal features. The ECG signal processing system 11 includes at least one micro processor which processes the ECG signal to obtain a plurality of ECG signal features. The compression rate estimate processing system 13 includes at least one micro processor which applies one or more of a plurality of criteria to the impedance signal features and the ECG signal features and uses compliance with one or more of the criteria to select one of the plurality of impedance signal compression rate estimates as the CPR compression rate. The output unit 15 receives the CPR compression rate and outputs feedback based on the CPR compression rate to a user of the defibrillator.

[0041] Referring to FIG. 2, the method of determining a CPR compression rate carried out by the defibrillator 1 of FIG. 1 includes one or more of: receiving an impedance signal of a subject (30), receiving an ECG signal of the subject (32), processing the impedance signal to obtain a plurality of impedance signal compression rate estimates (34), processing the impedance signal to obtain a plurality of impedance signal features (36), processing the ECG signal to obtain a plurality of ECG signal features (38), and applying a plurality of criteria to the impedance signal features and the ECG signal features and using compliance with one or more of the criteria to select one of the plurality of impedance signal compression rate estimates as the CPR compression rate (40).

[0042] Processing the impedance signal to obtain the plurality of impedance signal compression rate estimates 34 includes one or more of using a frequency domain transformation on the impedance signal to obtain an impedance signal frequency spectrum, using a peak detection algorithm to identify a plurality of peaks in the impedance signal frequency spectrum and determining central frequencies of the plurality of peaks as the plurality of impedance signal compression rate estimates.

[0043] Processing the impedance signal to obtain the plurality of impedance signal features 36 includes one or more of using a frequency domain transformation on the impedance signal to obtain an impedance signal frequency spectrum, using a peak detection algorithm to identify a plurality of peaks in the impedance signal frequency spectrum and determining central frequencies and amplitudes of the plurality of peaks as the plurality of impedance signal features. Processing the ECG signal to obtain the plurality of ECG signal features 38 includes using a frequency domain transformation on the ECG signal to obtain an ECG signal frequency spectrum, using a peak detection algorithm to identify a plurality of peaks in the ECG signal frequency spectrum and determining central frequencies and amplitudes of the plurality of peaks as the plurality of ECG signal features.

[0044] The transformation uses a FFT algorithm on a six second, advancing window of the impedance signal and a corresponding six second, advancing window of the ECG signal.

[0045] The peak detection algorithm identifies a plurality of peaks in the impedance signal frequency spectrum and ECG signal frequency spectrum by identifying peaks based on decreasing steepness of slopes of the spectra. In this embodiment, the peak detection algorithm returns two peaks from each frequency spectrum, a primary peak having a highest amplitude at its central frequency and a secondary peak having a next highest amplitude at its central frequency. An amplitude threshold, including a pre-determined number of standard deviations above background, is used to determine if the peaks are true peaks. The central frequencies of the primary peak and the secondary peak in the impedance signal frequency spectrum provide the impedance signal compression rate estimates. The central frequencies and amplitudes of the primary peak and the secondary peak in the impedance signal frequency spectrum provide the impedance signal features. The central frequencies and amplitudes of the primary peak and the secondary peak in the ECG signal frequency spectrum provide the ECG signal features.

[0046] Referring to FIG. 3, in this embodiment, the compression rate estimate processing system 13 of the defibrillator 1 applies four criteria to the impedance signal features and the ECG signal features and compliance is used to select one of the impedance signal compression rate estimates as the true CPR compression rate.

[0047] The first criterion applied by the compression rate estimate processing system 13 includes in the impedance signal frequency spectrum a ratio of a secondary peak amplitude and a primary peak amplitude being greater than a pre-determined impedance signal amplitude ratio threshold of 0.2. It will be appreciated that other impedance signal amplitude ratio thresholds may be used, such as, for example, thresholds in the range of 0.05 to 0.5, as well as other values outside of this range.

[0048] The second criterion applied by the compression rate estimate processing system 13 includes in the impedance signal frequency spectrum a central frequency of a primary peak being greater than a central frequency of a secondary peak. The third applied by the compression rate estimate processing system 13 criterion includes in the ECG signal frequency spectrum a central frequency of a primary peak being less than a central frequency of a secondary peak. The fourth criterion applied by the compression rate estimate processing system 13 includes a frequency difference between a lower frequency primary or secondary peak in the impedance signal frequency spectrum and a lower frequency primary or secondary peak in the ECG signal frequency spectrum being less than a pre-determined frequency difference threshold of 0.25 Hz. It will be appreciated that other frequency difference thresholds may be used, such as in a range between 0.05 and 0.5 Hz, or other values as well.

[0049] The compression rate estimate processing system 13 uses compliance with each of the first to fourth criteria to select an impedance signal compression rate estimate including a central frequency of the secondary peak of the impedance signal frequency spectrum as the CPR compression rate, as shown in the figure. Non-compliance with any of the first to fourth criteria is used by the compression rate estimate processing system 13 to select an impedance signal compression rate estimate including a central frequency of the primary peak of the impedance signal frequency spectrum as the CPR compression rate, as shown in the figure.

[0050] The CPR compression rate thus determined is passed to the output unit 15. This outputs feedback based on the CPR compression rate to the user of the defibrillator 1 including an indication that the CPR compression rate is any of satisfactory, too slow, too fast. Outputting the feedback based on the CPR compression rate to the user of the defibrillator provides the user with an opportunity to improve the quality of CPR and gives an indication of the effectiveness of the compressions.

[0051] Another aspect of this disclosure includes coverage for a non-transitory computer-readable storage device. For example, an embodiment can include a computer-readable storage device having instructions for controlling a processor, wherein, when the instructions are executed by the processor, the instructions cause the processor to perform operations including receiving an impedance signal of a subject, receiving an electrocardiogram (ECG) signal of the subject, processing the impedance signal to obtain a plurality of impedance signal compression rate estimates, processing the impedance signal to obtain a plurality of impedance signal features, processing the ECG signal to obtain a plurality of ECG signal features and applying a plurality of criteria to the impedance signal features and the ECG signal features and using compliance or non-compliance with one or more of the criteria to select one of the plurality of impedance signal compression rate estimates as the CPR compression rate.

[0052] Whether to practice the method or in connection with the defibrillator embodiment, where necessary, computer components are included within the scope of this disclosure. Such components can include, without limitation, a processor, a bus that communicates data between computer components, an input component, an output component, graphical user interfaces, speech processing or speech related components, multi-modal input components, various modules which include computer code programmed to cause the processor to perform certain functions as disclosed herein, or non-transitory computer-readable devices that store computer code or computer-implemented instructions, which, when implemented, cause a processor or a specific module to perform certain operations.