WO2017072055A1

WO2017072055A1 - System and method for monitoring spontaneous pulse and compressions using invasive arterial blood pressure during cardiopulmonary resuscitation

Info

Publication number: WO2017072055A1
Application number: PCT/EP2016/075472
Authority: WO
Inventors: Ralph Wilhelm Christianus Gemma Rosa WIJSHOFF; Jens MÜHLSTEFF
Original assignee: Koninklijke Philips N.V.
Priority date: 2015-10-27
Filing date: 2016-10-21
Publication date: 2017-05-04

Abstract

A cardiopulmonary resuscitation (CPR) monitoring device includes an invasive arterial blood pressure (iABP) transducer (20) connected with an arterial cannula or catheter (16) to measure an iABP signal (30). A CPR chest compressions sensor (14, 70, 72) measures a CPR chest compressions signal (74, 76). One or more electronic processors are programmed to: (i) extract a CPR chest compression rate from the CPR chest compressions signal; (ii) compute a CPR chest compressions component (42) of the iABP signal by fitting to the iABP signal a harmonic series whose fundamental frequency is set to the CPR chest compression rate, and (iii) compute a compressions free component (44) of the iABP signal as a difference between the iABP signal and the CPR chest compressions component of the iABP signal. A display component (51) displays at least the compressions free component of the iABP signal.

Description

System And Method For Monitoring Spontaneous Pulse And Compressions Using Invasive Arterial Blood Pressure During Cardiopulmonary Resuscitation

FIELD The following relates generally to the medical arts, medical emergency response arts, patient monitoring arts, cardiopulmonary resuscitation arts, and related arts.

BACKGROUND

Cardiopulmonary resuscitation (CPR) is indicated for cardiac arrest and is applied by manual chest compressions and rescue breaths. Automated CPR devices employing a compression robot are also known. The goal of CPR is to achieve return of spontaneous circulation (ROSC) in which the beating heart drives life-sustaining blood circulation. Quantitative blood pressure measurement is a key metric in assessing ROSC; however the blood pressure needed to provide life- sustaining circulation is variable from one patient to the next. Thus, while a blood pressure measurement can support a determination of ROSC, the clinician should evaluate other factors such as skin color, patient age, overall appearance, and so forth.

Ventricular fibrillation (VF) is one specific type of cardiac arrest. In VF, the electrical activity of the heart is unorganized, as a result of which the heart cannot properly contract. In VF, the heart is not beating and is therefore unable to maintain life- sustaining blood circulation. VF can be treated by electric defibrillation using an automated external defibrillator (AED), if one is available. Modern AED units are highly automated, and include an electrocardiography (ECG) signal and signal processing that automatically assesses the cardiac rhythm. The AED recommends defibrillation only if a "shockable" rhythm is detected, and the AED may be programmed to deliver the shock only if a shockable rhythm is detected.

Appropriate emergency care for a person suffering from cardiac distress requires rapid and accurate assessment of the state of the heart. A person in cardiac arrest should always receive CPR, whereas it depends on the electrical activity of the heart if electric defibrillation should be applied in conjunction with CPR. However, if CPR chest compressions are continued after ROSC is achieved, the continued chest compressions can result in re-arrest via compression-induced re-fibrillation. Thus, it is important to quickly and accurately detect when ROSC is achieved by administered CPR or cardiac defibrillation.

The potential for improperly continuing CPR chest compressions after achieving ROSC is heightened in automated CPR employing a compression robot. The robot does not become tired, and there is increased likelihood that the emergency responder may become distracted and fail to diligently monitor the arrested person for ROSC during automated chest compressions.

The ECG component of the AED generally does not provide reliable detection of ROSC, because cardiac electrical activity, even if organized, does not necessarily translate into physical heart contractions effective to deliver life-sustaining circulation. Manual palpation to detect arterial pulsations is the method currently employed most to assess whether the patient has ROSC. The wrist, femoral or carotid artery is usually palpated for this purpose. However, manual palpation cannot distinguish between a spontaneous pulse and blood circulation driven by CPR chest compressions. Therefore, chest compressions must be stopped to allow for pulse check by palpation. Such interruptions reduce the effectiveness of the chest compressions, and a trade-off must be made between the goal of delivering continuous chest compressions and the goal of rapid detection of ROSC. Current CPR guidelines call for alternating between 30 chest compressions followed by two ventilating breaths for a period of 2 min. After such a 2 min block, the ECG rhythm is analyzed by an AED (if available) or another monitor-defibrillator. If the ECG rhythm is shockable, the patient is shocked and a new 2 min block is initiated. If the ECG is organized, a pulse check by manual palpation follows. If there is no pulse, a new 2 min block is initiated. If there is a pulse, the clinician determines if it is appropriate to stop CPR and move to the post-ROSC phase, or if it is appropriate to shortly continue CPR. Guidelines state that pulse check by palpation should not take longer than 10 s. In practice, however, pulse checks can take up to 30 s.

Wijshoff et al., "Photoplethysmography-Based Algorithm for Detection of Cardiogenic

Output During Cardiopulmonary Resuscitation", IEEE Trans. On Biomedical Engineering vol. 62 no. 3 pp. 909-921 (2015) discloses a technique which uses photoplethysmography (PPG) to support detection of ROSC, which can be employed during CPR chest compressions. This approach can detect a spontaneous pulse waveform in the PPG signal during CPR chest compressions. However, photoplethysmography does not provide quantitative blood pressure information, and so a manual pulse check by palpation is needed to confirm the indication of ROSC provided by the automated PPG signal analysis.

Accordingly, there remains a continued need for improved techniques for quantitative support for ROSC detection during CPR chest compressions.

BRIEF SUMMARY

In accordance with one illustrative example, a cardiopulmonary resuscitation (CPR) monitoring device includes an invasive arterial blood pressure (iABP) transducer configured for connection with an arterial cannula or catheter to measure an iABP signal, a CPR chest compressions sensor configured to measure a CPR chest compressions signal, and one or more electronic processors programmed to: (i) extract a CPR chest compression rate from the CPR chest compressions signal; (ii) compute a CPR chest compressions component of the iABP signal by fitting to the iABP signal a harmonic series whose fundamental frequency is set to the CPR chest compression rate; and (iii) compute a compressions free component of the iABP signal as a difference between the iABP signal and the CPR chest compressions component of the iABP signal. The CPR monitoring device further includes a display component configured to display at least the compressions free component of the iABP signal, and in some embodiments is configured to display the CPR chest compressions component of the iABP signal and the compressions-free component of the iABP signal as parallel trend lines. The one or more electronic processors may be further programmed to identify time intervals over which CPR chest compressions are interrupted in the CPR chest compressions signal, and set the CPR chest compressions component of the iABP signal to zero in operation (iii) during the identified time intervals over which CPR chest compressions are interrupted. The one or more electronic processors may be further programmed to, prior to the computing operations (ii) and (iii), high-pass filter the iABP signal using a high-pass filter with a cut-off frequency of 0.7 Hz or lower. In some embodiments with automated detection of certain CPR events, the one or more electronic processors may be further programmed to detect a spontaneous pulse of amplitude greater than a ROSC-indication threshold amplitude and/or with a rate greater than a ROSC- indication threshold rate and/or with pulse intervals with variability below a ROSC-indication threshold variability in the compressions-free component of the iABP signal (30) and cause the display component to display an indication of ROSC and/or operate an alarm loudspeaker to sound in response to the detection. Additionally or alternatively, the one or more electronic processors may be further programmed to detect the amplitude of the CPR chest compressions component of the iABP signal being lower than a minimum threshold and cause the display component to display an indication and loudspeaker to sound a message that deeper CPR chest compressions are needed in response to detecting the amplitude of the CPR chest compressions component of the iABP signal is lower than the minimum threshold, and to detect the rate of the CPR chest compressions component of the iABP signal being outside a target range and cause the display component to display an indication and loudspeaker to sound a message that faster / slower CPR chest compressions are needed in response to detecting the rate of the CPR chest compressions component of the iABP signal is outside the target range. The foregoing CPR monitoring device embodiments may comprise a patient monitoring device including as a unitary assembly the display component and an electronic processor programmed to perform at least the computing operations (ii) and (iii).

In accordance with another illustrative example, a non-transitory storage medium stores instructions readable and executable by an electronic processing device to perform a CPR monitoring method comprising: computing a CPR chest compressions component of an invasive arterial blood pressure (iABP) signal by fitting to the iABP signal a harmonic series whose fundamental frequency is set to a CPR chest compression rate; and computing a compressions free component of the iABP signal as a difference between the iABP signal and the CPR chest compressions component of the iABP signal. The CPR monitoring method may further include identifying time intervals over which CPR chest compressions are interrupted, and setting the CPR chest compressions component of the iABP signal to zero during the time intervals over which CPR chest compressions are interrupted. The CPR monitoring method may further include, prior to the computing operations, high-pass filtering the iABP signal using a high-pass filter with a cut-off frequency of 0.7 Hz or lower.

One advantage resides in providing support for detection of ROSC during CPR chest compressions including quantitative assessment of blood pressure provided by the spontaneously beating heart. Another advantage resides in providing the foregoing advantage using medical diagnostics that are often already in place at the time of cardiac arrest of a hospitalized patient.

Further advantages of the present invention will be appreciated to those of ordinary skill in the art upon reading and understanding the following detailed description. It will be appreciated that a given embodiment may provide none, one, two, or more of these advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention.

FIGURE 1 diagrammatically illustrates a device for monitoring a subject undergoing cardiopulmonary resuscitation (CPR) using invasive arterial blood pressure (iABP).

FIGURE 2 diagrammatically illustrates an embodiment of the iABP compression component separator of the CPR monitoring device of FIGURE 1.

FIGURE 3 presents experimental porcine iABP data acquired using the CPR monitoring device of FIGURE 1 during cardiac arrest (left side) and after ROSC (right side).

DETAILED DESCRIPTION

With reference to FIGURE 1, a person 10 under cardiac arrest receives manual cardiopulmonary resuscitation (CPR) provided by an emergency responder 12. FIGURE 1 illustrates the emergency responder 12 providing manual CPR chest compressions. Alternatively, the emergency responder could strap a CPR compression robot 14 (if immediately available) onto the chest of the person 10 under cardiac arrest, and activate the CPR compression robot 14 to provide automated CPR chest compressions. The person 10 under cardiac arrest also has an invasive arterial blood pressure (iABP) sensor connected. The illustrative iABP sensor comprises an invasive arterial line including an arterial cannula or catheter 16 that is inserted into an artery of the patient 10 and attached fluid- filled tubing 18, typically filled with saline. The end of the tubing 18 distal from the arterial cannula or catheter 16 is connected with a pressure transducer 20 (preferably with automatic flushing). A pressure bag 22 is installed to maintain a pressurized fluid column. The iAPB transducer 20 outputs an iABP signal 30 that can be quantitatively correlated with arterial blood pressure (both in terms of waveform and amplitude). Alternatively, the iABP signal 30 can be obtained via a catheter with an electronic pressure-tip transducer which does not need a fluid-filled tubing, such as a Millar catheter.

The person 10 under cardiac arrest is typically a hospitalized patient in an intensive care unit (ICU), cardiac care unit (CCU), regular hospital room, or so forth, and the arterial line is commonly administered in such a hospital setting. However, the person 10 may be located elsewhere, such as in an ambulance en-transit between medical facilities, or may be a non-hospitalized person who has collapsed due to cardiac arrest and the arterial line has been installed "in the field" by a doctor or other trained emergency responder.

The iABP signal 30 will exhibit pulsations due to CPR chest compressions delivered manually by the emergency responder 12 or by the CPR compression robot 14. If these CPR chest compressions are successful in achieving a return of spontaneous circulation (ROSC), then the spontaneous pulse generated by the beating heart will also manifest as pulsations in the iABP signal 30. However, during CPR chest compressions it is difficult or impossible for a doctor or other medical professional to accurately discriminate between pulsations in an iABP signal trend line due to cardiac contractions versus pulsations due to CPR chest compressions. If CPR chest compressions are interrupted then an accurate assessment of ROSC can be made, but if this check indicates that the person 10 remains in cardiac arrest or that the heart is not (yet) generating sufficient pressure then this interruption of CPR chest compressions reduces the effectiveness of the CPR (that is, reduces the statistical likelihood that the CPR will ultimately achieve ROSC).

To overcome this difficulty, as disclosed herein an iABP compression component separator 40 processes the iABP signal 30, in conjunction with the CPR compression rate, to separate the iABP signal 30 into (I) a CPR chest compressions component 42 of the iABP signal 30 and (II) a compressions-free component 44 of the iABP signal 30. Both of these iABP signal components 42, 44 can be usefully consulted by an emergency responder providing CPR. The CPR chest compressions iABP component 42 provides information, in real-time, about whether the CPR chest compressions are effective to provide life-sustaining blood circulation. The CPR chest compressions iABP component 42 provides the arterial blood pressure waveform and also provides quantitative information about the amplitude (and rate) of the arterial blood pressure pulsations created by the CPR chest compressions. The latter provides valuable feedback based upon which the emergency responder can assess whether deeper (and faster / slower) CPR chest compressions are needed. The compressions-free iABP component 44, on the other hand, is consulted to assess whether ROSC has been achieved by the CPR. Until ROSC is achieved, the compressions-free iABP component 44 will exhibit no pulsations (i.e., it will be approximately "flat-line"). However, as soon as the heart resumes beating, the compressions-free iABP component 44 will exhibit pulsations attributable to the spontaneous pulse. The compressions-free iABP component 44 provides the arterial blood pressure waveform generated by the spontaneous pulse and also provides quantitative information about the amplitude of the arterial blood pressure pulsations created by the spontaneous pulse. The latter enables the emergency responder to assess whether the spontaneous pulse could be strong enough to provide life-sustaining blood circulation, i.e., this waveform can support the emergency responder in determining whether ROSC has been achieved.

Illustrative FIGURE 1 depicts a patient monitoring device 50 which includes a display component 51 (e.g., an LCD display, OLED display, or so forth) on which a trend line 52 of the CPR chest compressions iABP component 42 is displayed, and on which a trend line 54 of the compressions-free iABP component 44 is displayed. In other contemplated embodiments, only the CPR chest compressions iABP component 42 is displayed as a trend line. In other embodiments, only the compressions-free iABP component 44 is displayed as a trend line. Either one or both components 42, 44 may additionally or alternatively be displayed in another format, such as a real-time numeric value.

The emergency responder can view the parallel trend lines 52, 54 to assess progress of the CPR, in the CPR monitoring system of FIGURE 1. It is additionally or alternatively contemplated to provide visual and/or audio alarms to indicate key events during the CPR. For example, as diagrammatically illustrated in FIGURE 1 a ROSC indicator 60 monitors the compressions-free iABP component 44 to detect whether a spontaneous pulse of amplitude greater than a ROSC-indication threshold amplitude and/or with a rate greater than a ROSC- indication threshold rate and/or with pulse intervals with variability below a ROSC-indication threshold variability (these thresholds are generically denoted as threshold T_R0SC in FIGURE 1) is present in the compressions-free iAPB component 44. If this is the case, then the ROSC indicator 60 causes the display component 51 of the patient monitor 50 to display a ROSC indicator 62. Additionally or alternatively, the ROSC indicator 60 can activate an alarm loudspeaker 64 of the patient monitor 50 to alert the emergency responder of a potential ROSC. Preferably, the emergency responder is trained to perform a standard protocol upon noticing the visual or audible indication of ROSC, such as continuing CPR chest compressions for a standard time interval and then stopping compressions and performing a pulse check by palpation and other assessment (e.g. assessing skin color) to confirm ROSC; or, stopping compressions immediately and performing the pulse check by palpation and other ROSC assessment.

Additionally or alternatively, the patient monitor 50 can be programmed to issue a visual and/or audio alarm in response to a deficiency in the CPR chest compressions detected by automated analysis of the CPR chest compressions iABP component 42. For example, since the CPR chest compressions iABP component 42 provides quantitative assessment of the amplitude of arterial blood pressure pulsations generated by the CPR chest compressions, if the amplitude of the CPR chest compressions iABP component 42 is lower than a minimum threshold then an indicator 66 can be displayed informing the emergency responder that deeper CPR chest compressions are needed and/or an audible message can be sounded by the loudspeaker (which can be advantageous since the emergency responder providing chest compressions may not be looking at the patient monitor 50). This feedback can advantageously assist the emergency responder in setting the depth of the compressions (that is, adjusting how much force is used in compressing the chest during CPR chest compressions) to be enough to maintain life-sustaining blood circulation while not being excessive so as to limit the likelihood of physically injuring the person 10. Additionally, if the rate of the CPR chest compressions iABP component 42 is outside a target range then an indicator 66 can be displayed informing the emergency responder that faster / slower CPR chest compressions are needed and/or an audible message can be sounded by the loudspeaker. This feedback can advantageously assist the emergency responder in setting the rate of the compressions.

The iABP compression component separator 40 processes the iABP signal 30 in conjunction with the CPR compression rate to separate the CPR chest compressions iABP component 42 and the compressions-free iABP component 44. The CPR compression rate can be determined in various ways. In the illustrative example, the arrested person 10 has defibrillator pads 70 attached to the torso, via which an automated external defibrillator (AED) 72 may be used to deliver an electric defibrillation shock. As is known in the emergency response arts, cardiac defibrillation is only administered to a person who has an unorganized electrocardiography (ECG) signal, i.e., who is in ventricular fibrillation (VF). This may happen after ROSC was achieved but the heart then transitions into VF, which is a reasonably common occurrence. Moreover, the emergency responder 12 is usually initially uncertain as to whether the person 10 has an organized ECG signal or is in VF. Therefore, it is appropriate to attach the defibrillator pads 70 and start up the AED 72 so as to ensure its availability in the normal course of providing emergency assistance to the person 10. If the AED 72 is programmed to measure trans-thoracic impedance (TTI) between the defibrillator pads 70, then the TTI signal 74 can be input to the iABP compression component separator 40 which can determine the compression rate from periodicity of the TTI signal 74. More generally, any sensor that provides a signal that cycles with the CPR compressions can be analyzed to extract the compression rate: for example, an accelerometer, force sensor, a camera or radar attached to the torso of the patient 10 will provide such a signal. In another approach, if the CPR compression robot 14 is used to deliver CPR chest compressions at a programmed (or pre-set) CPR chest compression rate, then the compression rate can be received from the CPR compression robot 14, for example as a signal 76 indicating the programmed compression rate or as a reading of the analog control signal sent to the compression motor control component of the robot 14.

The iABP compression component separator 40, as well as any automated CPR event detectors such as the illustrative ROSC indicator 60, is suitably implemented as one or more electronic processors programmed to perform the functionality of these components 40, 60. In some embodiments, the patient monitoring device 50 includes as a unitary assembly the display component 51 and an electronic processor programmed to perform at least the separation of the iABP signal 30 into the component signals 42, 44. The electronic processor of the patient monitoring device 50 may also perform processing on the reference signal 74, 76 in order to derive the CPR chest compression rate. Furthermore, the patient monitoring device 50 may also include the defibrillation functionality and measurement of the TTI signal. In a variant embodiment, the processing of the reference signal 74, 76 to derive the CPR chest compression rate may be performed, for example, by an electronic processor of the AED 72 ancillary to the TTI sensor functionality, or may be performed by the CPR compression robot 14 to generate the signal 76 as a quantitative CPR chest compression rate value (e.g., as a digital rate value communicated by a USB cable or wirelessly by state-of-the-art technologies).

It will be further appreciated that the illustrative computational components 40, 60 may be embodied as a non-transitory storage medium storing instructions executable by an electronic processor (e.g. the patient monitoring device 50 and/or the AED 72) to perform the disclosed operations. The non-transitory storage medium may, for example, comprise a hard disk drive, RAID, or other magnetic storage medium; a solid state drive, flash drive, electronically erasable read-only memory (EEROM) or other electronic memory; an optical disk or other optical storage; various combinations thereof; or so forth.

With reference now to FIGURE 2, an illustrative embodiment of the iABP compression component separator 40 is described. In the illustrative embodiment of FIGURE 2, the iABP compression component separator 40 receives as inputs the iABP signal 30 and the trans-thoracic impedance (TTI) signal 74. Digital signal processing (DSP) 78 is performed on the TTI signal 74 to extract CPR compressions information 80 including compression rate, denoted herein as R [k], and also a CPR chest compressions "envelope", denoted A[k], which indicates when chest compressions are interrupted (typically to perform ventilation and/or a pulse check by palpation). In the illustrative example, A[k] = 0 during time intervals over which chest compressions are interrupted, and A[k] = 1 otherwise. More generally, the CPR compressions information 80 includes identification of time intervals over which chest compressions are interrupted. (It is noted that the illustrative iABP compression component separator 40 operates using digital signal processing (DSP), and as is conventional in DSP literature data samples as a function of time are indexed by time index k). The envelope A[k] may be extracted, for example, by applying a peak detector or a low-pass filter and thresholding and digitizing the peak or low-pass filtered signal. The compression rate R [k] can be extracted by a technique such as a Fast Fourier Transform (FFT) or other frequency-domain DSP to detect the fundamental frequency component of the TTI signal 74. Alternatively, the compression rate R [k] can also be determined by detecting the individual compressions in the TTI signal time-trace, which allows adjustment of R [k] from one compression to the next. The iABP signal 30 is optionally pre-processed to facilitate extraction of the component(s) corresponding to blood circulation pulsations due to chest compressions and/or spontaneous beating of the heart. In the illustrative embodiment, the iABP signal 30 is high-pass filtered using a high-pass filter 82 with a cut-off frequency of 0.7 Hz or lower to generate a high- pass filtered iABP signal 30HP. The cut-off frequency of the high-pass filter 82 is preferably chosen to pass the fundamental frequency component due to CPR chest compressions and (if present) spontaneous pulses while removing lower-frequency components that are too low to be due to CPR chest compressions or a life-sustaining pulse. A cut-off frequency of 0.5 Hz corresponds to 30 beats (or compressions) per minute, which is well below the recommended compression rate of 80-120 compressions per minute and is below a bradycardic heart rate of about 50 beats/minute. A lower cut-off frequency can be used, or the high-pass filter 82 can be omitted entirely, at the cost of increased noise. Conversely, a higher cut-off frequency can remove more extraneous signal but at increasing possibility of removing relevant compressions and/or pulse signal components. For example, the high-pass filter can have a cut-off frequency of 0.7 Hz (42 beats/min) or lower, but this could result in filtering out a very low heart rate. For the porcine experimental results reported herein with reference to FIGURE 3 (which are not human data), a high-pass filter with a cut-off frequency of 0.3 Hz (18 beats/min) was used.

The illustrative embodiment of the iABP compression component separator 40 shown in FIGURE 2 employs an adaptive algorithm that estimates the CPR chest compression component 42 in the iABP signal 30 by making use of the chest compression reference signal (e.g., the TTI signal 74). In illustrative FIGURE 2, the estimate of the CPR chest compressions iABP component 42 is by way of an operation 84 in which a harmonic series whose fundamental frequency is set to the CPR chest compression rate R [k] is fit to the iABP signal 30 (optionally after high-pass filtering, i.e. high-pass filtered iABP signal 30HP). By subtracting this estimate 42 from the iABP signal 30 (again, optionally after high-pass filtering, i.e. filtered signal 30HP) using a difference operation 86, the compression-free iABP component 44 is obtained, which provides an estimate of the spontaneous pulse pressure component (if present and thereby indicating that ROSC may have been achieved). In the embodiment of FIGURE 2, the IABP_HP signal 30HP (denoted in digitized form iABP_Hp [k]) is assumed to be a summation of a spontaneous pulse component sp [k], compression component cmp [k], and residual component r[k] : iABP_HP [k] = sp [k] + cmp [k] + r[k] ( 1) with the index k again denoting sample number k. The trans-thoracic impedance (TTI) signal 74 measured between the defibrillation pads 70 of the cardiac defibrillator 72 is used as an auxiliary input signal providing information on the chest compression frequency (and optionally the compressions phase). This information is subsequently used in a signal model or a physical model (e.g., a harmonic signal model is employed in operation 84) that describes the compression component cmp [k] of the high-pass filtered iABP signal iABP_HP [k]. This provides an estimate of the compression component in the iABP signal, indicated herein as cmp_est [k] and indicated in FIGURES 1 and 2 as the compressions iABP component 42. By subtracting the estimate of the compression component from the (optionally high-pass filtered) iABP signal, the compression-free iABP signal component is obtained which provides an estimate of the spontaneous pulse component in the iABP signal 30, denoted herein as sp_est[k] : sPesAk] = iABP_HP [k] - cmpesAk] (2) where the compression-free iABP signal is indicated by sp_est[k]. This signal sp_est[k] is indicated in FIGURES 1 and 2 as the compressions-free iABP component 44. By showing the compression-free iABP signal 44 on the display component 51 of the patient monitor 50 as the trend line 54, the emergency responder is provided with feedback on the status of the heart of the patient 10 which supports determining when it is appropriate to interrupt the CPR chest compressions in order to further investigate the condition of the heart, e.g., by interrupting CPR chest compressions and performing a pulse check by palpation. On the other hand, if there is no spontaneous pulse component (compressions-free iABP component 44 is flat line) or only a small spontaneous pulse component or a spontaneous pulse component at a low rate or a spontaneous pulse component with large variability in the beat-to-beat intervals in the compression-free iABP signal 44, the clinician may decide that it is most appropriate to continue the CPR chest compressions. Optionally, the ROSC indicator 60 (see FIGURE 1) monitors the compressions-free iABP component 44 to detect whether a spontaneous pulse of amplitude greater than a ROSC-indication threshold amplitude is present and/or with a rate greater than a ROSC-indication threshold rate and/or with pulse intervals with variability below a ROSC- indication threshold variability, and activates a suitable human-perceptible alarm 62, 64 if this is the case. On the other hand, displaying the trend line 52 of the estimate of the compression component 42 of the iABP signal 30 provides the emergency responder with feedback on the effectiveness of the CPR chest compressions when the heart has resumed beating. Since the impact of CPR chest compressions on the arterial blood pressure is being measured by the compression iABP component 42 (rather than measuring a surrogate such as impact of compressions on photoplethysmography), the amplitude of the compression iABP component 42 is a quantitative indication of effectiveness of the CPR compressions, and can optionally be measured automatically to automatically issue a human-perceptible alarm 66 if, for example, the compressions provide insufficient circulation.

In one illustrative embodiment, the compressions iABP component 42 is modelled in the operation 84 by a harmonic signal model of N_H sinusoidal harmonic components:

N_H

cmp_est [k] = A[k] ^ a_m[k]cos(mq) [k]) + b_m[k]sin(mq)[k]) (3) m=l where N_H is the number of harmonic components, A[k] is the CPR chest compressions envelope (A[k] = 0 during intervals over which CPR chest compressions are interrupted and A[k] = 1 otherwise), and < [/c] is an instantaneous compression phase (in radians):

where R [k] is the CPR chest compression rate (in Hertz, i.e. compressions per second) extracted from the CPR chest compressions signal, T_s is the sample interval [s], and φ₀ is an arbitrary constant phase offset (in radians). The coefficients _m [/c] and b_m [k] of the harmonic series of Expression (3) can be estimated using a least mean-square (LMS) algorithm or other optimization algorithm to fit the harmonic model of Expression (3) to the high-pass filtered iABP signal iABP_HP [k]. The resulting compressions iABP signal component cmp_est[k] is input to the difference operation 86 suitably implemented as Expression (2) to generate the compressions- free iABP component sp_est [k] .

Fitting the harmonic series of Expression (3) effectively fits the phase of the compressions iABP component cmp_est [k] by fitting both the in-phase and quadrature harmonic coefficients _m [/c] and b_m [k]. As a consequence, the choice of φ₀ in Expression (4) can be arbitrary as any "error" in φ₀ is removed by the fitting. This can be more explicitly seen in the alternative formulation of the harmonic series as:

cmp_est [k] = A (5)

where in this formulation the fitted parameters of the harmonic series are now the harmonic component amplitude P_m [k] and phase _πι [k] in radians.

By having the fitted parameters _m[/c] and b_m [k] of Expression (3) (or, if Expression (5) is used, the fitted parameters P_m [k] and 0_m [/c]) be functions of sample [k], the harmonic model is adaptive - that is, it can adapt to changes in the CPR compressions rate R [k] or phase φ_πι [k] over time. However, an emergency responder trained in providing CPR should provide relatively steady chest compressions for which the compression rate R [k] and phase φ_πι [k] are expected to vary relatively slowly in time. If automated CPR is performed using the compressions robot 14 then the CPR compression rate and phase should be constant (R [k]→ R). To provide fast adaptive response on the order of two CPR chest compression cycles or faster, it is contemplated to implement the feedback fitting loop of FIGURE 2 using an analog or digital phase-locked loop (PLL) or frequency-locked loop (FLL) architecture.

With reference now to FIGURE 3, porcine experimental data have been collected demonstrating efficacy of the disclosed approach of FIGURES 1 and 2 in supporting detection of ROSC. The top trend line 30P,HP shown in FIGURE 3 is the iABP signal acquired for a test pig subject after high-pass filtering using a high-pass filter with cut-off frequency of 0.3 Hz. This corresponds to the digitized signal iAPB_HP [k] described herein and indicated as high-pass filtered iABP signal 30HP in FIGURE 2. The center trend line 42p shown in FIGURE 3 is the compression iABP component cmp_est[k] indicated as compressions component 42 in FIGURES 1 and 2. The bottom trend line 44p shown in FIGURE 3 is the compression-free iABP component sp_est[k] indicated as compression-free component 44 in FIGURES 1 and 2. The trend lines of FIGURE 3 illustrate the pig in cardiac arrest (left hand portion 90) and after ROSC (right hand portion 92) responsive to a defibrillation shock 94 (indicated by a dashed line). In FIGURE 3, time intervals during which chest compressions were administered are indicated by the notation "CC"; while time intervals during which chest compressions were interrupted for ventilation are indicated by the notation "V". The CPR protocol employed was 30 compressions alternated by two ventilations, with CPR chest compressions delivered at a rate of 100 compressions/minute.

Prior to the cardiac defibrillation shock 94 the pig was in cardiac arrest (left side 90), and this is reflected by a nearly flat line for the compression-free iABP component sp_est [k] (trend line 44p in region 90). After delivery of the defibrillation shock 94, the pig's heart was restarted so that ROSC was achieved, and this is reflected in an observed spontaneous pulse in the compression-free iABP component sp_est[k] (trend line 44p in region 92). The high-pass filtered trend line 30HP exhibits increased complexity after ROSC (i.e. in region 92 compared with region 90), but it would be difficult for the emergency responder to determine whether this complexity is due to a life- sustaining pulse, or is instead due to artifacts in the iABP signal, random cardiac fibrillations, or so forth. By contrast, the compressions iABP signal component 42p remains relatively steady in amplitude after ROSC (region 92) albeit with some quasi- random amplitude modulation due to incomplete signal separation. The emergency responder can observe the compression depth translated to iABP modulation in the compressions iABP signal component 42p in region 92. Both the amplitude and frequency of the spontaneous pulse is readily observed in the compressions-free iABP signal component 44p in region 92. Additionally, it can readily be observed in the compressions-free iABP signal component 44p in region 92 that the heart is contracting at stable intervals. Also noteworthy is that the compressions iABP signal component 42p goes to identically zero during the ventilations (time intervals labeled "V") due to A [k] = 0 being set in these ventilation time intervals. Very little in the way of artifacts is seen in the compression-free iABP component sp_est[k] (trend line 44p) at transitions between compressions (CC) and ventilations (V), and the heart rate shown by the compression-free iABP component sp_est [k] in region 92 (after ROSC) in particular is seen to be visually smooth.

The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be constructed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMS:

1. A cardiopulmonary resuscitation (CPR) monitoring device comprising:

an invasive arterial blood pressure (iABP) transducer (20) configured for connection with an arterial cannula or catheter (16) to measure an iABP signal (30);

a CPR chest compressions sensor (14, 70, 72) configured to measure a CPR chest compressions signal (74, 76);

one or more electronic processors programmed to:

(i) extract a CPR chest compression rate from the CPR chest compressions signal,

(ii) compute a CPR chest compressions component (42) of the iABP signal by fitting to the iABP signal a harmonic series whose fundamental frequency is set to the CPR chest compression rate, and

(iii) compute a compressions-free component (44) of the iABP signal as a difference between the iABP signal and the CPR chest compressions component of the iABP signal; and

a display component (51) configured to display at least the compressions-free component of the iABP signal.

2. The CPR monitoring device of claim 1 wherein the display component (51) is configured to display the CPR chest compressions component (42) of the iABP signal (30) and the compressions-free component (44) of the iABP signal as parallel trend lines (52, 54).

3. The CPR monitoring device of any one of claims 1-2 wherein the CPR chest compressions sensor comprises a trans-thoracic impedance (TTI) sensor (70, 72), an accelerometer, a force sensor, a camera or a radar.

4. The CPR monitoring device of any one of claims 1-2 wherein the CPR chest compressions sensor comprises:

a trans-thoracic impedance (TTI) sensor of an automated external defibrillator (AED)

(72).

5. The CPR monitoring device of any one of claims 1-2 further comprising:

a CPR compression robot (14) configured to automatically perform CPR chest compressions at a programmed compression rate;

the CPR chest compressions sensor (14, 70, 72) comprising the CPR compression robot configured to output the CPR chest compressions signal indicating the programmed compression rate.

6. The CPR monitoring device of any one of claims 1-5 wherein the one or more electronic processors is further programmed to:

identify time intervals over which CPR chest compressions are interrupted in the CPR chest compressions signal, and

set the CPR chest compressions component (42) of the iABP signal (30) to zero in operation (iii) during the identified time intervals over which CPR chest compressions are interrupted.

7. The CPR monitoring device of any one of claims 1-6 wherein the one or more electronic processors is further programmed to:

prior to the computing operations (ii) and (iii), high-pass filter the iABP signal using a high-pass filter (82) with a cut-off frequency of 0.7 Hz or lower.

8. The CPR monitoring device of any one of claims 1-7 wherein the one or more electronic processors is further programmed to:

detect a spontaneous pulse of amplitude greater than a return of spontaneous circulation (ROSC) indication threshold amplitude and/or with a rate greater than a ROSC-indication threshold rate and/or with pulse intervals with variability below a ROSC-indication threshold variability in the compressions-free component (42) of the iABP signal (30) and cause the display component (51) to display an indication (62) of ROSC in response to the detection.

9. The CPR monitoring device of any one of claims 1-8 further comprising:

an alarm loudspeaker (64);

wherein the one or more electronic processors is further programmed to (iv) detect a spontaneous pulse of amplitude greater than a return of spontaneous circulation (ROSC) indication threshold amplitude and/or with a rate greater than a ROSC-indication threshold rate and/or with pulse intervals with variability below a ROSC-indication threshold variability in the compressions-free component (42) of the iABP signal (30) and activate the alarm loudspeaker in response to the detection.

10. The CPR monitoring device of any one of claims 1-9 wherein the one or more electronic processors is further programmed to:

detect the amplitude of the CPR chest compressions component (42) of the iABP signal (30) being lower than a minimum threshold and cause the display component (51) to display an indication (66) and sound a message that deeper CPR chest compressions are needed in response to detecting the amplitude of the CPR chest compressions component of the iABP signal is lower than the minimum threshold, and

detect the rate of the CPR chest compressions component (42) of the iABP signal (30) being outside a target range and cause the display component (51) to display an indication (66) and a loudspeaker to sound a message that faster / slower CPR chest compressions are needed in response to detecting the rate of the CPR chest compressions component of the iABP signal is outside the target range.

11. The CPR monitoring device of any one of claims 1-10 comprising a patient monitoring device (50) including as a unitary assembly the display component (51) and an electronic processor programmed to perform at least the computing operations (ii) and (iii).

12. A non-transitory storage medium storing instructions readable and executable by an electronic processing device (50) to perform a cardiopulmonary resuscitation (CPR) monitoring method comprising:

computing a CPR chest compressions component (42) of an invasive arterial blood pressure (iABP) signal (30) by fitting to the iABP signal a harmonic series whose fundamental frequency is set to a CPR chest compression rate; and

computing a compressions-free component (44) of the iABP signal as a difference between the iABP signal and the CPR chest compressions component of the iABP signal.

13. The non-transitory storage medium of claim 12 wherein the electronic processing device comprises a patient monitoring device (50) including an electronic processor and a display component (51) and the CPR monitoring method further comprises:

displaying, on the display component of the patient monitoring device, a trend line (54) of the compressions-free component (44) of the iABP signal (30).

14. The non-transitory storage medium of any one of claims 12-13 wherein the electronic processing device comprises a patient monitoring device (50) including an electronic processor and a display component (51) and the CPR monitoring method further comprises: displaying, on the display component of the patient monitoring device, a trend line (52) of the CPR chest compressions component (42) of the iABP signal (30).

15. The non-transitory storage medium of any one of claims 12-14 wherein the CPR monitoring method further comprises:

extracting the CPR chest compression rate from a signal generated by a trans-thoracic impedance (TTI) sensor (70, 72), by an accelerometer, a force sensor, a camera or a radar sensor.

16. The non-transitory storage medium of any one of claims 12-14 further comprising: receiving the CPR chest compression rate from a CPR compression robot (14) configured to automatically perform CPR chest compressions.

17. The non-transitory storage medium of any one of claims 12-16 wherein the CPR monitoring method further comprises:

identifying time intervals over which CPR chest compressions are interrupted, and setting the CPR chest compressions component (42) of the iABP signal (30) to zero during the time intervals over which CPR chest compressions are interrupted.

18. The non-transitory storage medium of any one of claims 12-17 wherein the CPR monitoring method further comprises:

prior to the computing operations, high-pass filtering the iABP signal using a high-pass filter (82) with a cut-off frequency of 0.7 Hz or lower.

19. The non-transitory storage medium of any one of claims 12-18 wherein the CPR monitoring method further comprises:

detecting a spontaneous pulse of amplitude greater than a return of spontaneous circulation (ROSC) indication threshold amplitude and/or with a rate greater than a ROSC- indication threshold rate and/or with pulse intervals with variability below a ROSC-indication threshold variability in the compressions-free component (44) of the iABP signal (30) and causing an output component (51, 64) of the electronic processing device (50) to generate a human-perceptible output (62) indicating potential ROSC in response to detecting the spontaneous pulse of amplitude greater than the ROSC threshold amplitude and/or with a rate greater than a ROSC-indication threshold rate and/or with pulse intervals with variability below a ROSC-indication threshold variability.

20. The non-transitory storage medium of any one of claims 12-19 wherein the CPR monitoring method further comprises:

detecting the amplitude of the CPR chest compressions component (42) of the iABP signal (30) being lower than a minimum threshold and causing an output component (51) of the electronic processing device (50) to generate a human-perceptible output (66) indicating that deeper CPR chest compressions are needed in response to detecting the amplitude of the CPR chest compressions component of the iABP signal is lower than the minimum threshold, and detecting the rate of the CPR chest compressions component (42) of the iABP signal (30) being outside a target range and causing an output component (51) of the electronic processing device (50) to generate a human-perceptible output (66) indicating that faster / slower CPR chest compressions are needed in response to detecting the rate of the CPR chest compressions component of the iABP signal is outside the target range.