DEVICE, SYSTEM AND METHOD FOR SUPPORTING DETECTION OF RETURN OF SPONTANEOUS CIRCULATION DURING CARDIOPULMONARY RESUSCITATION

Abstract

The present invention relates to a device, system and method providing quantitative support for detection of return of spontaneous circulation during cardiopulmonary resuscitation. A photoplethysmography measurement is used to trigger a blood pressure measurement for assessing return of spontaneous circulation and hence for guiding a user through CPR. The present invention may prevent futile interruptions during compressions as well as re-arrest of the heart due to unnecessary compressions.

Claims

1. device for supporting detection of return of spontaneous circulation during cardiopulmonary resuscitation, the device comprising a PPG input configured to obtain one or more photoplethysmography, PPG, signals of a patient; a BP output configured to provide a BP control signal for controlling a BP sensor to start measuring blood pressure, BP, of the patient; a BP input configured to obtain one or more BP measurements; and a processing unit configured to analyze one or more predefined PPG signal properties of the one or more PPG signals and to generate the BP control signal if one or more of the PPG signal properties fulfill a predefined condition, wherein the one or more PPG signal properties correspond to one or more of pulse presence, pulse rate, pulse strength, and duration of the pulse presence of the patient, wherein the processing unit is configured to assess a status of an indicator of cardiogenic output indicating return of spontaneous circulation based on a combination of the one or more PPG signals with the BP measurements.

2. The device according to claim 1, wherein the predefined condition includes one or more of a threshold, a range, an item in a look-up table, a position in a chart, and a comparison with a stored PPG waveform.

3. The device according to claim 1 further comprising an ECG input configured to obtain one or more ECG, electrocardiography, signals, wherein the processing unit is configured to analyze the one or more predefined PPG signal properties using the one or more ECG signals.

4. The device according to claim 1, further comprising a chest compression signal input configured to obtain a chest compression signal indicating one or more of trans-thoracic impedance, chest compression rate, length of inter-compression intervals, chest compression force, chest compression depth, chest compression acceleration and chest compression velocity, wherein the processing unit is configured to analyze the chest compression signal and to recognize and handle or remove artifacts of said chest compression signal from the one or more PPG signals and/or the ECG signals; and optionally wherein the processing unit (40) is configured to analyze the chest compression signal to discriminate a pause in compressions from ongoing compressions and to generate the BP control signal during the pause in compressions or during ongoing compressions.

5. (canceled)

6. The device according to claim 1, further comprising a user input configured to obtain user information from a first user interface, wherein the processing unit is configured to generate the BP control signal and/or to adjust the predefined condition based on the user information, and/or further comprising a user output configured to provide ROSC information to a second user interface.

7. A system for supporting detection of return of spontaneous circulation during cardiopulmonary resuscitation, the system comprising one or more PPG sensors configured to measure one or more PPG signals; the device as claimed in claim 1 configured to generate a BP control signal by use of the one or more PPG signals; and a BP sensor configured to perform BP measurements based on the BP control signal; wherein the device is configured to assess a status of an indicator of cardiogenic output indicating return of spontaneous circulation based on a combination of the one or more PPG signals with the BP measurements.

8. The system according to claim 7, wherein the BP sensor is comprised of a BP cuff which can be any one of a finger cuff, wrist cuff and arm cuff, and wherein the one or more PPG sensors are configured to be arranged in one of said cuffs, one or more other finger, wrist or arm cuffs or at the patient's finger, earlobe, concha or pinna of the ear, forehead, alar wing or septum of the nose and/or the inside of the mouth, such as the cheek or the tongue.

9. The system according to claim 8, wherein the processing unit is configured to control the cuff pressure continuously or in intervals during ongoing compressions or during pauses in compressions.

10. The system according to claim 7, wherein at least one of the one or more PPG sensors is configured to be arranged at a skin facing side of the BP cuff, and wherein the processing unit is configured to control a mean cuff pressure applied to the patient by said cuff to maximize an amplitude of the one or more PPG signals of the at least one PPG sensor and/or an oscillation of pressure inside said cuff.

11. The system according to claim 7, further comprising one or more ECG sensors configured to measure one or more ECG signals, wherein the processing unit is configured to analyze the one or more ECG signals to facilitate obtaining any one of the one or more PPG signal properties, and/or further comprising a chest compression sensor configured to measure a chest compression signal indicating one or more of trans-thoracic impedance, chest compression rate, length of inter-compression intervals, chest compression force, chest compression depth, chest compression acceleration and chest compression velocity, wherein the processing unit is configured to analyze said chest compression signal and to recognize and handle or remove artifacts of said chest compression signal from the one or more PPG signals and/or ECG signals.

12. The system according to claim 7, further comprising a first user interface configured to obtain the user information and/or a second user interface to provide the ROSC information in a visible and/or audible manner.

13. A method for supporting detection of return of spontaneous circulation during cardiopulmonary resuscitation, the method comprising obtaining one or more photoplethysmography, PPG, signals of a patient; providing a BP control signal for controlling a BP sensor to start measuring blood pressure, BP, of the patient; obtain one or more BP measurements; analyzing one or more predefined PPG signal properties of the one or more PPG signals and generating the BP control signal if one or more of the PPG signal properties fulfill a predefined condition, wherein the one or more PPG signal properties correspond to any one of pulse presence, pulse rate, pulse strength, and duration of the pulse presence of the patient; and assessing a status of an indicator of cardiogenic output indicating return of spontaneous circulation based on a combination of the one or more PPG signals with the BP measurements.

14. A computer program comprising program code means for causing a computer to carry out the steps of the method as claimed in claim 13 when said computer program is carried out on the computer.

15. The device (10) according to claim 1, wherein the one or more PPG signal properties correspond to one or more of duration at a predefined pulse rate level, variation of inter-pulse intervals over time, a number of cardiac-induced harmonics, and a PPG waveform.

16. The method of claim 13, wherein the one or more PPG signal properties correspond to one or more of duration at a predefined pulse rate level, variation of inter-pulse intervals over time, a number of cardiac-induced harmonics and a PPG waveform.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. In the following drawings

[0054] FIG. 1 shows a schematic diagram of a first embodiment of a device for supporting detection of return of spontaneous circulation during cardiopulmonary resuscitation according to the present invention,

[0055] FIG. 2 shows a schematic diagram of a second embodiment of a device according to the present invention,

[0056] FIG. 3 shows a schematic diagram of a third embodiment of a device according to the present invention,

[0057] FIG. 4 shows a schematic diagram of a first embodiment of a system for supporting detection of return of spontaneous circulation during cardiopulmonary resuscitation according to the present invention,

[0058] FIG. 5 shows a schematic diagram of a second embodiment of a system for supporting detection of return of spontaneous circulation during cardiopulmonary resuscitation according to the present invention,

[0059] FIG. 6 shows an exemplary implementation of a system for supporting detection of return of spontaneous circulation of a patient undergoing CPR according to the present invention,

[0060] FIG. 7 shows an embodiment of a display unit of a device according to the present invention, and

[0061] FIGS. 8A and 8B show different embodiments of BP and PPG sensors according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0062] FIG. 1 shows a schematic diagram of a first embodiment of a device 10 for supporting detection of return of spontaneous circulation during cardiopulmonary resuscitation according to the present invention. The device 10 comprises a PPG input 20, a BP output 30 and a processing unit 40. The PPG input 20 is configured to obtain a PPG signal 21 of a patient and to provide said signal 21 to the processing unit 40. Subsequently, the processing unit 40 analyzes the PPG signal 21. In this embodiment, the processing unit 40 is configured to detect a pulse rate of the patient using said signal 21.

[0063] Detection of the pulse rate provides information about the rate at which the heart contracts and pumps blood. If the rate is below a predefined threshold, for example 0.5 Hz, the processing unit assumes that there is no ROSC yet. Hence, no other action than continuing the PPG measurement will be performed. Even if the analysis of the PPG signal 21 shows a rate high enough for potential ROSC, chest compressions should be continued if the heart does not yet pump in a stable fashion i.e. if the variation of inter-pulse intervals over time is too high. However, when the heart is pumping again at a stable rate higher than, e.g., 0.5 Hz, it is examined whether there is cardiogenic output by ordering a subsequent blood pressure measurement.

[0064] In fact, presence of a stable pulse rate which is sufficiently high is a necessary prerequisite of ROSC: without such a rhythm, there will be no ROSC, and it will be of no use to do a further assessment of cardiogenic output and correspondingly ROSC. On the other hand, presence of a stable, sufficiently high pulse rate in the PPG signal does not directly indicate that there is ROSC, because it does not provide quantitative information about the underlying blood pressure and/or level of perfusion. In other words, return of spontaneous circulation is only given once a perfusing rhythm has been re-established, i.e. when the heart contracts again at a stable rate resulting in a life-sustaining cardiac output. Hence, if the pulse rate is above the predefined threshold and fulfills a stability condition the processing unit 40 generates a BP control signal 31. The BP output 30 then provides the BP control signal for controlling a BP sensor to start measuring the blood pressure of the patient in order to support assessing ROSC.

[0065] FIG. 2 shows a schematic diagram of a second embodiment of a device 10 for supporting detection of return of spontaneous circulation during cardiopulmonary resuscitation according to the present invention. Apart from a PPG input 20, a BP output 30 and a processing unit 40, the device 10 also comprises a BP input 35 configured to obtain a BP measurement 36. By analysing the blood pressure signal 36 of the patient the processing unit 40 may assess return of cardiogenic output or a probability of return of spontaneous circulation. ROSC is probably given if, for example, the systolic blood pressure is higher than 60 mmHg. Therefore, the processing unit 40 is configured to check whether the blood pressure is above said or another predefined threshold. If this is the case, the processing unit 40 assesses return of cardiogenic output. A clinician may then stop delivering chest compressions to a patient in order to prevent re-arrest or other damages due to chest compressions and/or to assess ROSC.

[0066] FIG. 3 shows a schematic diagram of a third embodiment of a device 10 according to the present invention. The device 10 comprises a PPG input 20, a BP output 30, a BP input 35, a chest compression signal input 50, a user input 60 and a processing unit 40.

[0067] A PPG signal 21 obtained by the PPG input 20 is communicated to the processing unit 40 for analysis. The PPG signal 21 is analyzed for presence of a spontaneous pulse during compressions. Presence of a spontaneous pulse in the PPG signal 21 during compressions can be recognized by an increased complexity in the shape of the PPG signal 21, for example. Alternatively, pulse presence can be detected via spectral analysis of the PPG signal, when two harmonic series can be identified, one of which corresponding to chest compressions and the second of which corresponding to cardiac activity.

[0068] Analysis during ongoing compressions also involves using a chest compression reference 51 to detect presence of compressions and to identify the compression rate. The compression reference 51 may be an impedance signal obtained between defibrillation pads attached to the patient, for example. The chest compression signal input 50 is configured to obtain the chest compression signal 51. The chest compression signal 51 indicates the rate of chest compressions delivered to the patient, the variation of inter-compression intervals over time and the compression strength and/or depth, respectively. The processing unit 40 analyzes said properties of the chest compression signal 51. Using the analysis results the processing unit 40 then removes artifacts of the chest compression signal 51 from the PPG signal 21 by removing all frequency components related to the measured compression rate. This way, motion artifacts due to chest compressions complicating detection of a cardiac pulse in the PPG signal 21 are eliminated or attenuated. Alternatively, the processing unit 40 uses the compression rate derived from the compression reference 51, to identify and ignore all spectral components in the PPG signal related to the compressions in order to determine whether the PPG signal contains remaining spectral components related to cardiac activity. E.g., when the processing unit 40 detects two harmonics series in the PPG signal 21, the compression rate information can be used to identify which of these two harmonic series corresponds to chest compressions and which of these two harmonic series corresponds to spontaneous cardiac activity.

[0069] The processing unit 40 of this embodiment is further configured to analyze the chest compression signal 51 to discriminate a pause in compressions from ongoing compressions. If the compression signal is determined to indicate a compression rate below a predefined threshold or is determined not to contain compression-related characteristics, the processing unit 40 assesses that there are no chest compressions delivered to the patient, i.e. that there is a pause in compressions. Identifying a pause in compressions based on the compression signal 51 can be used to obtain an alternative detection of presence or absence of the spontaneous cardiac component in the PPG signal 21. Given that there is a pause in compressions and that pulse presence is detected in the PPG signal 21, where pulse presence is detected during ongoing compressions and/or during a pause in compressions, the processing unit 40 generates a BP control signal 31 during the pause in compressions. The BP output 30 takes said signal to control a BP sensor for measuring the blood pressure of the patient. Apart from that, the processing unit 40 may be used to extract information about the quality of CPR components such as compression depth or chest compression fraction.

[0070] The device 10 for detecting return of spontaneous circulation further comprises a user input 60 configured to obtain user information 61 from a first user interface 600 and to provide ROSC information 71 to a second user interface 700 (see FIG. 5). The processing unit 40 uses the user information 61 in order to generate the BP control signal 31. User information 61 may comprise a confirmation to start the BP measurement, for example. Hence, if the PPG signal analysis results in a high probability for ROSC, the processing unit 40 can first prompt to the user via user interface 700 that cardiogenic output has been detected and request whether a BP measurement should be performed. Only after the user confirmed that performing a BP measurement is appropriate via user interface 600, the BP control signal is generated to initiate the BP measurement. This allows the clinician to determine the moment at which performing a BP measurement is most appropriate. Furthermore, user information provided via user interface 600 can be used to customize thresholds and ranges used in the assessment of the status of the indicator of cardiogenic output. These thresholds and ranges can relate to pulse presence, PR, duration of a (minimum) PR level, pulse intervals, duration of pulse presence, variations in pulse intervals, pulse strength, BP, duration of a specified BP level, the number of cardiac-induced harmonics detected in the PPG signal.

[0071] FIG. 4 shows a schematic diagram of a first embodiment of a system 100 for supporting detection of return of spontaneous circulation during cardiopulmonary resuscitation according to the present invention. The system 100 comprises the second embodiment of the device 10 for supporting detection of return of spontaneous circulation, a PPG sensor 201, a BP sensor 300 and an ECG sensor 900.

[0072] The BP sensor 300 is integrated in a cuff 301 in this embodiment. Said cuff may be applied to the patient's finger and measure his or her blood pressure during compressions, e.g., by tracking the Mean Arterial Pressure, MAP. Tracking of blood pressure would be performed after presence of pulse was detected in the PPG signal. The PPG measurement module 201 is integrated in the same cuff 301, in particular underneath, i.e. at the skin facing side of, said cuff 301. The PPG and cuff-based pressure measurement can be performed on the middle or proximal phalanx of a finger, in particular on the proximal phalanx of the thumb. The PPG sensor 201 is continuously measuring the PPG signal 21 of the patient, which is measured at, e.g. green, red and/or infrared wavelengths, respectively. The measured PPG signal 21 is communicated to the processing unit 40 for subsequent analysis. In particular, the PPG signal 21 is analyzed for presence of a spontaneous pulse during compressions. Said analysis is supported by the ECG signal 91 provided by the ECG sensor 900 via the ECG input 90. In particular, the ECG signal should first have an organized appearance before analyzing the PPG signal for presence of pulse. That is, the ECG signal should first contain QRS-complexes, which indicates that the heart's electrical activity has been restored again, which is called return of rhythm, ROR. After ROR has occurred, the heart's mechanical activity can be checked for by searching for cardiac-induced pulses in the PPG signal. The QRS complexes in the ECG signal can facilitate detecting the cardiac-induced pulses in the PPG signal, as the cardiac-induced PPG pulses should follow these QRS complexes when the heart is beating. Alternatively, when applying spectral analysis the heart rate (HR) derived from the ECG signal can be used to identify the pulse rate (PR) of the spontaneous pulses in the PPG signal.

[0073] After presence of a spontaneous pulse has been detected in the signal 21 with the help of the ECG signal analysis, the cuff-based BP measurement is triggered. To this end, the processing unit 40 is configured to scan the cuff pressure to find the mean arterial pressure (MAP). The MAP is approximated by the cuff pressure at which the spontaneous pulse component in the PPG signal has maximum pulsatility, i.e. maximum amplitude or maximum average signal level. At maximum pulsatility, the vascular compliance is maximum meaning that the vascular wall is unloaded. Unloading of the vascular wall is achieved when the cuff pressure equals the mean blood pressure in the vessel. Alternatively, the pressure oscillations inside the cuff 301 are measured. Then, the MAP is approximated by the cuff pressure at which the pressure oscillations in the cuff 301 have maximum amplitude as measured by the BP sensor 300.

[0074] The MAP can also be estimated during cardiac arrest. Then the pulsatility of the compression-induced component in the PPG signal 21 or the amplitude of the compression-induced component in the cuff pressure is maximized.

[0075] Alternatively, in another embodiment, the PPG measurement and the BP measurement are not integrated in the same cuff. Here, the PPG measurement could for instance be obtained using a PPG sensor 201 applied to a finger, the forehead, the nasal septum, the alar wing, the earlobe, the concha of the ear, or the pinna of the ear. The BP measurement could be obtained using a cuff 301 applied to the arm, wrist or finger. Once presence of a spontaneous pulse is detected in the PPG signal 21, the cuff-based BP measurement can be triggered. If the cuff 301 would be applied to the upper arm and the PPG measurement would be applied to a digit on the other arm, the BP measurement could run while at the same time the PPG measurement is still being used to track pulse presence. Alternatively, if the PPG measurement would be applied distal to the cuff 301 on the same arm, the PPG measurement could be used to determine BP levels. For instance, when scanning pressure in the arm cuff 301, an estimate of the systolic blood pressure (SBP) would be reached when the spontaneous pulse disappears in the PPG measurement performed distally to the cuff.

[0076] FIG. 5 shows a schematic diagram of a second embodiment of a system for supporting detection of return of spontaneous circulation according to the present invention. The system comprises the third embodiment of the device 10, a PPG sensor 201, a BP sensor 300, a chest compression sensor 500, a first user interface 600 and a second user interface 700.

[0077] In this embodiment of the system 100, the PPG sensor 201 is incorporated in a finger cuff 301. At the same time, said cuff contains the BP sensor 300. The BP measurement performed by the cuff is a continuous non-invasive blood pressure measurement (cNIBP). A cNIBP measurement needs to be calibrated to find the mean digital arterial pressure around which the processing unit 40 can track variations in blood pressure. In this embodiment, calibration for the cNIPB measurement is performed during ongoing compressions. The mean pressure corresponds to the cuff pressure at which the pulsatility of the PPG signal 21 is maximum (pulsatility =amplitude divided by average signal level). Said pressure is determined by the processing unit 40. At maximum pulsatility, the vascular compliance is maximum which means that the vascular wall is unloaded. Unloading of the vascular wall is achieved when the cuff pressure equals the mean blood pressure in the vessel. Tracking the mean blood pressure and thus the operating point of the cNIBP measurement allows for a more rapid cNIBP measurement in a subsequent pause in compressions, because the correct mean pressure has already been estimated and the cNIBP measurement can start right away. In this embodiment, the operating point of the cNIBP measurement can be tracked continuously over time or at regular intervals in time.

[0078] The pulsatility of the PPG signal 21 can be maximized either during cardiac arrest or after detection of a spontaneous pulse in the PPG signal 21. During cardiac arrest, the pulsatility of the compression-induced signal is maximized. After detection of a spontaneous pulse, the pulsatility of the spontaneous pulse component in the PPG signal 21 is maximized. In order to maximize the pulsatility of the spontaneous pulse component, said component is extracted from the PPG signal 21 by removing chest compression artifacts. Removal of chest compression components involves use of a compression reference signal 51 to determine the chest compression rate.

[0079] This way, when the PPG-measurement is performed underneath the finger cuff, the mean digital arterial pressure can be tracked during compressions. Tracking the mean digital artery blood pressure during compressions has the following advantages: First, it makes sure that the cNIBP measurement is always at its operating point and ready for use, and second, it improves the quality of the PPG measurement by maximizing the signal amplitude. In fact, when the PPG-measurement is performed underneath the finger-cuff, the cuff can continuously apply a low pressure to assure good signal quality by maximizing the PPG signal pulsatility. This improves the signal-to-noise ratio and quality of the PPG measurement 21. Furthermore, the cuff pressure assures good contact between the PPG sensor 201 and the skin, which reduces motion of the PPG sensor 201 relative to the skin and thereby motion artifacts in the PPG signal 21. Moreover, during cardiac arrest, by tracking the mean digital artery blood pressure the processing unit 40 can assess the effectiveness of the chest compressions.

[0080] The second user interface 700 may display the PPG signal time-trace, in particular after removal of chest compression artifacts, the blood pressure measurements (SBP, MAP, DBP), and the cNIBP time-trace, as well as derived information such as an indicator of cardiogenic output to provide clinical decision support. The interface 700 may also show the spontaneous pulse rate derived from the PPG measurement and the oxygen saturation (SpO2) determined from the spontaneous pulse component in the PPG measurements at, e.g., a red and an infrared wavelengths. Furthermore, the user interface 700 may provide audible feedback on the effectiveness of the chest compressions and give advice to the user to improve CPR.

[0081] FIG. 6 shows an exemplary implementation of a system 100 for supporting detection of return of spontaneous circulation of a patient undergoing CPR according to the present invention.

[0082] The system 100 comprises a device 10, a PPG sensor 201 arranged in a finger cuff, a BP sensor 300 arranged in an inflatable arm cuff, a chest compression sensor 500 attached to the patient's chest and subject to compression, two ECG sensors attached to the patient's chest, a first user interface 600 arranged in the device 10 and a second user interface 700. Chest compressions can be delivered either manually by a clinician 8, for example, or with an automated mechanical device 80.

[0083] In this embodiment of the system 100, PPG signal 21 can be measured during a pause in compressions and is used to schedule a BP measurement in the same pause in compressions, wherein the pause in chest compressions can be detected via the compression signal 51 being delivered via a chest compression cable 55 from the chest compression sensor 500 to the device 10. The PPG signal 21 being delivered via a PPG cable 25 from the finger cuff 201 to the device 10 is analyzed for presence of a spontaneous pulse. In order to support said analysis there are used the ECG signals measured by the ECG sensors 901 and 902 and provided to the device 10 via an ECG cable 95. The ECG signals 91 and 92 can be analyzed to detect QRS complexes, which indicate return of rhythm, ROR. After detection of ROR, the PPG signal 21 can be analyzed to find presence of pulse. Here, the ECG signals 91 and 92 can be helpful too, as the cardiac-induced pulses in the PPG signal 21 follow the QRS-complexes in the ECG signals 91 and 92. Alternatively, when applying spectral analysis, the heart rate (HR) derived from the ECG signals 91 and 92 can facilitate determining the pulse rate (PR) in the PPG signal 21. If a spontaneous pulse is detected in the PPG signal 21 during a pause, the cuff-based BP measurement is scheduled. The BP measurement can then be automatically performed directly after the detection of a spontaneous pulse.

[0084] Alternatively, the system can prompt to the clinician via a display or with an audible signal of the second user interface 700 that a spontaneous pulse has been detected and suggest to start the cuff-based BP measurement directly after pressing a button of the first user interface 600. In the latter case, the clinician 8 has the option to postpone the BP measurement, in case it is already clear to the clinician that the pulse cannot yet be life-sustaining. Furthermore, the system 100 may also measure and analyze PPG signal 21 for pulse presence during ongoing compressions. In that case, a BP measurement can be performed during the next pause in compressions, either automatically or after a confirmation from the user via user interface 600. If compressions are delivered in cycles of two minutes, for instance, as is customary in CPR, the BP measurement can be scheduled for the short pause directly following the two minute cycle of compressions. Alternatively, the system can prompt to the clinician 8 that a spontaneous pulse has been detected and suggest starting the BP measurement directly after pressing a button. In the latter case the clinician 8 has the option not to wait for the next pause in the protocol, but deviate from the standard protocol to personalize the treatment to a patient.

[0085] The BP measurement can be performed to measure systolic, diastolic and/or mean arterial blood pressure. The type of blood pressure to be measured may be decided by the user 8 using the user interface 600. In particular, the user interface 600 may be configured to enable the user to change the inflation and/or deflation rate of a BP cuff. The user may also provide user information with respect to the local hospital CPR protocol he/she uses. The measured BP signal 31 is provided to the device 10 via a BP cable 37. Using the BP measurements it is decided by the device 10 whether a cardiogenic output has been achieved (or how high the probability is for ROSC). The thresholds and ranges used in the assessment of the status of the indicator of cardiogenic output can be customized by the user via user interface 600. These thresholds and ranges can relate to pulse presence, PR, duration of a (minimum) PR level, pulse intervals, duration of pulse presence, variations in pulse intervals, pulse strength, number of cardiac-induced harmonics detected in the PPG signal, BP, duration of a specified BP level. If the status assessment of the indicator of cardiogenic output decides for pulse presence, the processing unit 40 provides corresponding information to the display 700 indicating to the clinician 8 that a further assessment of ROSC is advised. If ROSC has probably not been achieved, however, a new two-minute block of CPR is suggested via the display or is directly initiated to be performed by the mechanical CPR device 80.

[0086] The PPG measurement can be performed on the same arm as where the BP measurement is performed distal to the cuff 301, or on the other arm not used for BP measurements. A BP measurement would be performed after pulse presence has been detected in the PPG signal 21. In the first case, where the PPG measurement is performed distal to the cuff 301, the PPG measurement can no longer be used for pulse presence detection during the BP measurement. However, in this case the PPG measurement could be used to determine BP levels. For instance, when scanning pressure in the arm cuff 301, an estimate of the systolic blood pressure (SBP) would be reached when the spontaneous pulse disappears in the PPG measurement performed distally to the cuff 301. Alternatively, when the PPG measurement is performed on a digit on the other arm than where the BP measurement is performed, the BP measurement could run while at the same time the PPG measurement is still being used to track pulse presence.

[0087] FIG. 7 shows an exemplary implementation of a second user interface 700 of a system 100 according to the present invention.

[0088] In this implementation, the second user interface 700 is a display unit showing tracking of a diastolic blood pressure signal 32, oscillations 33 of said signal and a chest compression signal 51 over time. The diastolic blood pressure 32 and the oscillations 33 are depicted on a 0-50 mmHg pressure scale. The oscillations 33 can be seen to be in direct relation with the chest compression signal 51.

[0089] The processing unit 40 processes the measured PPG and BP data 21 and 31 to determine the status of an indicator of cardiogenic output, which has a continuous scale ranging from “cardiac arrest” to “potential ROSC”. Said scale is also displayed on the display unit 700 as a ROSC probability bar 45. An indicator 46 indicates in real-time the probability of ROSC as assessed by the processing unit. Hence, the user is immediately informed once a potentially life-sustaining pulse has been detected and may therefore decide to stop CPR actions on a re-started heart and further assess the potential ROSC.

[0090] FIGS. 8A and 8B show different embodiments of BP and PPG sensors according to the present invention.

[0091] FIG. 8A shows a finger cuff 301 wrapped around a finger 9 comprising both a PPG sensor 201 and a BP sensor 300. In this embodiment, a continuous non-invasive blood pressure measurement is achieved via a volume clamping cuff. The PPG sensor 201 integrated in the cuff comprises a red LED and an infrared LED as light sources and a photodiode for detecting light emitted by said sources and reflected by/transmitted through the patient's skin. Here the PPG measurement is used continuously to detect the presence of pulse. Once a pulse has been detected, the blood pressure measurement is triggered. As the BP measurement is based on the volume clamping method, the PPG measurement can no longer be used during the BP measurement. The volume-clamping based method can be used continuously or intermittently after pulse presence has been detected via PPG. In case of intermittent BP measurements, the PPG measurement can be used alternatingly with the BP measurement to keep tracking pulse presence.

[0092] For the determination of certain vital signs certain light colour ranges for the PPG signal 21 have shown best results. Furthermore, while the patient's pulse rate can be determined using a single wavelength, corresponding to, e.g., red, infrared or green, clear information about the oxygenation level of the blood (SpO2) providing further indication for ROSC can only be given using at least two different wavelengths for analysis. For example, the relative amplitude ratio of the wavelength interval around 650 nm (red) and 840 nm or 900 nm (infrared) has been shown to give reliable results for SpO2.

[0093] In the embodiment of BP and PPG sensors shown in FIG. 8B three PPG sensors 201, 202 and 203 are combined with a finger-cuff 301 for BP measurements, i.e. comprising a BP sensor, wrapped around a patient's finger 9. While the first PPG sensor 201 is arranged on the finger's skin distal to the cuff 301, the second PPG sensor 202 is arranged at a skin-facing side inside the cuff 301, and the third PPG sensor 203 is located on the patient's skin proximal to the cuff 301.

[0094] In this embodiment, the spontaneous pulse component in the signal of the first PPG sensor 201 is used to determine the systolic blood pressure (SBP). After a spontaneous pulse has been detected in the first PPG signal 21, the cuff-based BP measurement is triggered. The cuff-pressure is scanned to determine the SBP. This can be done during compressions or during a pause in compressions. If done during compressions, the SBP can be obtained in various ways. The cuff 301 is inflated until the spontaneous pulse component disappears in the first PPG signal 21, where the spontaneous pulse component has been extracted from the first PPG signal 21. The cuff pressure at which this happens is an estimate of the SBP. Alternatively, when the spontaneous pulse component is not explicitly extracted from the PPG signal 21, the SBP is approximated by the cuff-pressure at which the PPG signal amplitude/variance is minimized, as some compression artifacts in the PPG signal may not result from compression-induced pressure-waves propagating through the vessels but rather result from compression-induced sensor-tissue motion. Next, a blood pressure waveform can be obtained, by using the cuff 301 with the second PPG sensor 202 with a volume-clamping method for measuring cNIBP during a pause in compressions. The pulse pressure measured by cNIBP is a good estimate, but the absolute level of the cNIBP waveform needs to be calibrated. The calibration will here be performed using the SBP measurement obtained with the first PPG sensor 201. The systolic pressure in the cNIBP waveform is set equal to the SBP estimate obtained with the first PPG sensor 201. This allows for a measurement of the diastolic blood pressure (DBP) as well. During use of the volume-clamping method in the compression pause, the first PPG sensor 201 may provide unreliable results because the pulse signal is influenced upstream by a cuff. Therefore, during the cNIBP measurement, a third PPG sensor 203 can be used for PR and SpO2 measurements.

[0095] 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.

[0096] 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. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0097] A computer program may be stored/distributed on a suitable non-transitory medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0098] Any reference signs in the claims should not be construed as limiting the scope.