WO2010004499A1

WO2010004499A1 - Automated cardio pulmonary resuscitation apparatus with blood perfusion feedback

Info

Publication number: WO2010004499A1
Application number: PCT/IB2009/052927
Authority: WO
Inventors: Pierre H. Woerlee; Thomas J. De Hoog; Igor W. F. Paulussen; Shervin Ayati
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-07-11
Filing date: 2009-07-06
Publication date: 2010-01-14

Abstract

The invention relates to an apparatus, a method, a computer program product, and a signal for automated cardio pulmonary resuscitation. The apparatus comprises a chest compression actuator (102), an actuator driver (110) that supplies time- varying drive signals to the chest compression actuator in dependence of operating parameters of the actuator driver, a physiological parameter sensor (107) supplying measured values of a physiological parameter related to blood perfusion, an operating parameter adjuster (108) that uses the measured values for optimizing blood perfusion by consecutively modifying the operating parameters to new settings and evaluating for which one of the settings the measured value related to blood perfusion is optimal. The basic ideas on which this application is based are: separation of the servo feedback related to the compression pulse shape and depth and the feedback of perfusion related physiological data and usage of two independent feedback loops.

Description

Automated cardio pulmonary resuscitation apparatus with blood perfusion feedback

FIELD OF THE INVENTION

The invention relates to the field of automated cardiopulmonary resuscitation, and more specifically to optimizing blood perfusion during administering automated cardiopulmonary resuscitation. The invention addresses an automated cardiopulmonary resuscitation apparatus, a method for automated cardiopulmonary resuscitation, a computer program corresponding to the method, and a signal within an automated cardiopulmonary resuscitation apparatus.

BACKGROUND OF THE INVENTION Cardiopulmonary resuscitation (CPR) is a well-known technique for increasing the chance for survival from cardiac arrest. However, it is very difficult to perform manual cardiopulmonary resuscitation with consistent high quality. Since CPR quality is key for survival there is a strong drive to have a mechanical automated device to replace less reliable and long duration manual chest compressions. Automated CPR (A-CPR) apparatuses were introduced in the market recently.

Some A-CPR apparatuses use a pneumatic actuator mechanism while other A- CPR apparatuses are driven by an electrical motor such as a servo motor. Patent application publication US 2007/0270724 Al describes a servo motor for CPR that features a control of the compression wave form as applied to the patient. To this end US 2007/0270724 Al proposes to adjust the set point wave form. This leads to improved therapy concerning both blood flow and avoidance of internal injuries, because the desired wave form can be chosen relatively close to upper limits that should never be exceeded.

US patent number 7,190,999 describes an apparatus for assisting a rescuer in performing manual CPR on a victim. The apparatus comprises a SpO2 sensor for measuring blood oxygenation. A prompting device audibly conveys one or more actions that the rescuer should perform to improve the manual CPR. Although the apparatus may recommend to the rescuer to press harder, the ultimate control over the compression force remains in the hands and the responsibility of the rescuer. It is believed that compressions administered by a human rescuer, in particular when untrained, tend to be rather too weak than too strong. Furthermore, it is very difficult for a rescuer to consistently adhere to the feedback concerning modifications of the compression pulse.

SUMMARY OF THE INVENTION It would be desirable to achieve an automated cardiopulmonary resuscitation apparatus that takes into consideration the physical properties and the current health state of the patient. It would also be desirable to enable an automated cardiopulmonary resuscitation apparatus to find an efficient, yet safe mode of operation in a largely automated manner. To better address one or more of these concerns, in a first aspect of the invention an automated cardiopulmonary resuscitation apparatus is presented that comprises a chest compression actuator and an actuator driver that supplies time- varying drive signals to the chest compression actuator in dependence of operating parameters of the actuator driver. The automated cardiopulmonary resuscitation apparatus also comprises a physiological parameter sensor that supplies measured values of a physiological parameter related to blood perfusion. The automated cardiopulmonary resuscitation apparatus also comprises an operating parameter adjuster. The operating parameter adjuster uses the measured values for optimizing blood perfusion by consecutively modifying the operating parameters to new settings and by evaluating for which one of the settings the measured value related to blood perfusion is optimal. The operating parameters may for example be the compression cycle, the duty rate, the rise time, hold time, or the fall time of a compression.

It would be further desirable to provide an automated cardiopulmonary resuscitation apparatus that is capable of closely following a desired compression wave form. In an embodiment this concern is addressed by the actuator driver comprising an inner control loop. The inner control loop comprises a sensor for a parameter related to chest compression and an inner loop controller. The sensor supplies a chest compression measurement. The inner loop controller receives the chest compression measurement and performs closed loop control on the chest compression actuator in accordance with a desired chest compression wave form. The operating parameters comprise control settings of the inner loop controller and/or of the desired compression wave form. Furthermore, it would be desirable to have the automated cardiopulmonary resuscitation apparatus operate in a mode in which blood perfusion is as good as possible under the prevailing circumstances. In an embodiment this concern is addressed by the automated cardiopulmonary resuscitation apparatus further comprising an outer control loop that comprises the physiological parameter sensor and the operation parameter adjuster. The separation between an inner control loop and an outer control loop accounts for the significant differences in the dynamic behavior of the chest compression movement on the one side and blood perfusion on the other side. A related concern is assuring stability of the system output, i.e. the chest compression movement. The outer control loop is relatively independent from the inner control loop.

It would be desirable to provide an automated cardiopulmonary resuscitation apparatus that requires no or only little assistance from the rescuer for optimizing its operating parameters. At the same time, it would be desirable that an automatic optimization is unharmful for the patient, yet efficient. In an embodiment this concern is addressed by the operating parameter adjuster comprising a compression counter, a memory, a tendency analyzer, and an evaluator. The memory stores past and present records of operating parameters and associated measured values after a predetermined number of compressions. The tendency analyzer uses the measured values. The evaluator uses a result of the tendency analyzer for a decision as to increase, decrease, or maintain a particular operating parameter. As the settings of the operating parameters are modified the memory collects several samples so that at least a tendency of the blood perfusion can be observed after two or more samples. Eventually, a local blood perfusion maximum can be determined indicating a presumably preferred setting of operating parameters for the automated cardiopulmonary resuscitation apparatus. It is sufficient to sample one record every n compressions, because blood perfusion varies rather slowly compared to the compressions. It should be understood, that the number of compressions after which a new value is measured does not need to be constant, but is allowed to vary. The evaluator usually selects the one setting of operating parameters for which blood perfusion is highest among the records stored in the memory. This selection is, however, subject to exceptions and deviations. It would be further desirable to provide an automated cardiopulmonary resuscitation apparatus that is sensitive to the detection of external disturbances that translate to a deviation in the blood perfusion. Such a capability would assist the optimization procedure. In an embodiment this concern is addressed by the tendency analyzer being capable of detecting abnormal variations in the measured values and also being capable of outputting a corresponding indication. In this embodiment the evaluator uses the indication to restart from default values.

It would also be desirable to provide an automated cardiopulmonary resuscitation apparatus that can find a reasonable compromise between efficiency of blood perfusion and reducing the risk of damage to the thorax. This concern is addressed in one embodiment in that the evaluator selects a first setting instead of a second setting, if the first setting causes less expected thorax damage than a second setting, and if the measured values corresponding to the first setting are only insignificantly less optimal than the measured values corresponding to the second setting. For most victims, the probability of thorax damage increases strongly for a compression depth greater than 5 cm. This value of 5 cm is based on guidelines for cardio pulmonary resuscitation and corresponds roughly to a value of 20% of the anterior-posterior diameter (A-P diameter) for average patients. However, for some victims 6 cm could be optimal, in particular when the A-P diameter of the victim is large. In general, the maximal admissible compression depth should be limited to 20% of the A-P diameter. The apparatus could comprise an input device, either a sensor or the user is allowed to enter the A-P diameter, at least in an approximate manner ("slim", "normal", "large").

It would be desirable to provide an automated cardiopulmonary resuscitation apparatus that can distinguish between two or more different types of blood perfusion measurement. For example, the carotid blood flow (CBF) is representative for the brain perfusion. Under certain circumstances, it is advisable to prioritize blood perfusion of the brain over other organs. In an embodiment this concern is addressed by the automated cardiopulmonary resuscitation apparatus further comprising a second physiological parameter sensor supplying second measured values for a second physiological parameter related to blood perfusion of the brain. In this embodiment the operating parameter adjuster is prioritized to optimize the operating parameters so as to maximize the blood perfusion of the brain.

Turning now to a method for automated cardiopulmonary resuscitation, it would be desirable to provide such a method that supports an automated optimization of the operating parameter or a corresponding automated cardiopulmonary resuscitation apparatus. To better address this concern and possibly also other concerns, in a second aspect of the invention a method for automated cardiopulmonary resuscitation is presented that comprises: setting operating parameters of an automated cardiopulmonary resuscitation apparatus to safe initial values, the automated cardiopulmonary resuscitation apparatus performing at least one chest compression, collecting a measured value of a blood perfusion related physiological parameter, evaluating the measured value with respect to compliance with predetermined conditions, modifying the operating parameters to new settings, and evaluating for which one of the settings the measured value related to blood perfusion is optimal. The modification of the operating parameters is constrained by predetermined bounds for safe operation to avoid possible damage to the patient. When one operating parameter is getting close to its boundary, the variations from one setting to another setting can be chosen to have a smaller step size for this operating parameter. At the same time, the actual compression wave form, the blood perfusion, or other measurable physiological parameters could be analyzed for noticeable irregularities.

It would also be desirable to perform each chest compression uniformly and in accordance with a desired wave form. In an embodiment this concern is addressed by a method that further comprises: setting a desired wave form, - collecting chest compression measurements, performing closed loop control on a chest compression actuator within an inner control loop so that the chest compression measurements substantially fit the desired wave form.

Furthermore, it would be desirable to optimize blood perfusion and maintain the operational stability of the automated cardiopulmonary resuscitation apparatus. In an embodiment this concern is addressed in that the method further comprises performing outer loop control based on the measured value of the blood perfusion related physiological parameter. The separation between an inner control loop and an outer control loop leads to a stable and simple closed loop control. It would be desirable to provide a method for automated cardiopulmonary resuscitation by which operating parameters of an automated CPR apparatus can be set. In an embodiment this concern is addressed by the method further comprising: el) increasing the operating parameter by a certain step, e2) performing further chest compressions with the increased operating parameter, e3) collecting a new measured value of the blood perfusion related physiological parameter and determining a variation compared to the previously collected measured value, fl) comparing the variation to a predetermined threshold, f2) increasing, decreasing, or maintaining the operating parameter in dependence of a result of comparing. It would also be desirable to provide a method for automated cardiopulmonary resuscitation that prioritizes blood perfusion of highly important organs, such as the brain. In an embodiment this concern is addressed by the method further comprising: cl) collecting a second measured value of a second physiological parameter related to blood perfusion of the brain,

O) evaluating whether evaluation of the second measured value shows the same tendency in terms of improvement as a variation of the measured value, f4) in case of divergent tendencies, prioritizing the second physiological parameter and selecting a brain perfusion oriented setting among the settings so that blood perfusion of the brain is favored.

It would be furthermore desirable to achieve a computer program that assists in optimizing blood perfusion during automated cardiopulmonary resuscitation. To better address this concern and possible other concerns, in a third aspect of the invention a computer program is presented that enables a processor to carry out the method described above.

It would be furthermore desirable to achieve a signal within an automated cardio pulmonary resuscitation apparatus that assists in optimizing blood perfusion during automated cardiopulmonary resuscitation. To better address this concern and possible other concerns, in a fourth aspect of the invention a signal is presented that is transmitted from a physiological parameter sensor to an operating parameter adjuster of an automated Cardio Pulmonary Resuscitation apparatus, the physiological parameter sensor supplying measured values of a physiological parameter related to blood perfusion.

It would also be desirable to provide a signal for optimizing operating parameters of an automated cardiopulmonary resuscitation apparatus in view of blood perfusion. To better address this concern and possible other concerns, in a fourth aspect of the invention a signal is presented that is transmitted from a physiological parameter sensor to an operating parameter adjuster of an automated cardiopulmonary resuscitation apparatus. The physiological parameter sensor supplies measured values of a physiological parameter related to blood perfusion.

One of the basic ideas of the invention is to provide a feedback to an automated cardiopulmonary resuscitation apparatus. The feedback is based on a physiological parameter that is related to blood perfusion and thus the very goal of most cardiopulmonary resuscitations. The different technical features can be arbitrarily combined and such combination is herewith disclosed. In particular, but not exclusively, an automated cardiopulmonary resuscitation apparatus may comprise any combination of the following: a chest compression actuator, an actuator driver, a physiological parameter sensor for a parameter related to blood perfusion, an operating parameter adjuster, a sensor for a parameter related to chest compression, an inner loop controller, an inner control loop, an outer control loop, a compression counter, a memory storing past and present records of operating parameters and associated measured values, a tendency analyzer, an evaluator, a second physiological parameter sensor supplying second measured values for a second physiological parameter related to blood perfusion of the brain. In relation to a method for automated cardiopulmonary resuscitation any combinations of the actions described above is possible and herewith disclosed. In particular, and by no means exclusively, two or more of the following actions can be combined: setting operating parameters of an automated cardiopulmonary resuscitation apparatus to safe and sure values, the automated cardiopulmonary resuscitation apparatus performing at least one chest compression, collecting a measured value of a blood perfusion related physiological parameter, - evaluating the measured value with respect to compliance with predetermined conditions, modifying the operating parameters to new settings, evaluating for which one of the settings the measured value related to blood perfusion is optimal, - setting a desired wave form, collecting chest compression measurements, performing closed loop control on a chest compression actuator within an inner control loop so that the chest compression measurements substantially fit the desired wave form, - performing outer loop control based on the measured value of the blood perfusion related physiological parameter, increasing the operating parameter(s) (e.g. chest compression depth) by a certain step, performing further chest compressions with the increased operating parameter(s), collecting a new measured value of the blood perfusion related physiological parameter and determining a variation compared to the previously collected measured value, comparing the variation to a predetermined threshold, - increasing, decreasing, or maintaining the operating parameter(s) in dependence of a result of comparing, collecting a second measured value of a second physiological parameter related to blood perfusion of the brain, evaluating whether a variation of the second measured value shows the same tendency, in terms of improvement, as a variation of the measured value, in case of divergent tendencies, prioritizing the second physiological parameter and selecting a brain perfusion oriented setting among the settings so that blood perfusion of the brain is favored.

Equally, a computer program product is herewith disclosed as enabling a processor to carry out a method comprising any combination of two or more of the actions listed above.

Also disclosed herein is a signal between any of the components of an automated cardiopulmonary resuscitation apparatus as listed above.

This application also discloses the use of physiological parameters related to brain and heart perfusion to personalize automated cardio pulmonary resuscitation, in particular for a servo based apparatus. Also disclosed in the use of two separate feedback loops for the compression pulse form and the physiology parameters. The optimization should strive towards the best possible value for the patient rather than for a certain fixed number. If a trade-off between two or more physiological parameters is to be made, perfusion to the brain usually has higher priority. When using a controller in an automated cardio pulmonary resuscitation apparatus for CPR optimization, low cost sensors can be added to the A-CPR apparatus.

The various embodiments of this invention may solve one or more of the following problems: Interaction of the feedback loops related to the mechanical parameters and the perfusion related physiological parameters.

Optimization methods for automated cardio pulmonary resuscitation including physiological parameter input.

Selection of CPR parameters that can be varied. Reduction of interactions between (undesired) changes in compression waveform and CPR parameter variations.

Integrating the control in the automated CPR apparatus or in a smart automated external defibrillator (AED). The basic ideas on which some of the embodiments in this application are based are: separation of the servo feedback related to the compression pulse shape and depth and the feedback of perfusion related physiological data usage of two independent feedback loops optimization and incorporation of large changes not related to the CPR itself in these physiological parameters selection of CPR parameters that can be varied.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described herein after.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a schematic block diagram of an automated cardio pulmonary resuscitation apparatus according to a first aspect of the invention.

Fig. 2 shows a more detailed block diagram of an operating parameter adjuster.

Fig. 3 shows a flow chart of a method for automated cardio pulmonary resuscitation according to a first aspect of the invention.

Fig. 4 shows a flow chart of a method for automated cardio pulmonary resuscitation according to a second aspect of the invention. Fig. 5 shows a basic flow chart of a method for automated cardio pulmonary resuscitation when two physiological parameters are measured.

Figures 6 to 9 are diagrams showing different dependencies of a pair of physiological parameters from a change of an operating parameter.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 shows a schematic block diagram of an automated cardio pulmonary resuscitation apparatus according to a first aspect of the invention. The automated cardio resuscitation apparatus uses a chest compression actuator 102 that exerts a force on a human chest 104 by use of e.g. a pad and a piston. The chest 104 is not a part of the automated cardio pulmonary resuscitation apparatus and is represented by a mechanical model that approximates the mechanical behavior of the chest 104. The mechanical model can be represented by a spring and a damper connected in parallel. The movement of the pad, and consequently also the compression of the chest, is detected by a physiological parameter sensor 106 that provides measurements for the actual chest compression yk. The measurements of the actual chest compression yk are supplied, by means of a connection for the measurements for the actual chest compression 106, to a controller 112 that compares the actual chest compression y_k with a desired waveform for the chest compression ya and determines a drive signal Uk for the chest compression actuator 102. The drive signal Uk is supplied to the chest compression actuator 102 by means of a connection 101. The chest compression actuator 102, the chest of the patient 104, the physiological parameter sensor 106, and the controller 112 form a closed loop control system that assures a good tracking of the actual chest compression waveform y_k relative to the desired compression waveform ya. This closed loop control system is bordered by a dotted rectangle in Fig. 1 and can be regarded as an inner control loop.

The goal of any cardio pulmonary resuscitation is to improve blood perfusion of the patient or at least of the patient's vital organs. The degree and the quality of blood perfusion depend on the way the cardio pulmonary resuscitation is performed. Parameters of the cardio pulmonary resuscitation such as compression depth, compression rate, waveform, duty cycle, compression velocity and the like may have an influence on the blood perfusion. It is therefore expected that blood perfusion can be improved if an optimal combination of operating parameters can determined.

The dependency of blood perfusion from the compression is illustrated in Fig. 1 by an arrow from the stylized human chest 104 to an entity 105 referenced by PFSN for "perfusion". A sensor for a physiological parameter related to blood perfusion 107 (called blood perfusion sensor in the following) is placed on the patient and is capable of determining the degree of blood perfusion. Blood perfusion related parameters are among others: blood flow (pulse photoplethysmography, sPO2, CW and PW ultrasound Doppler techniques, ...), blood pressure, ETCO₂ and/or oxygen saturation. Besides sensor 107, further sensors for various other physiological parameters could be present and deliver measurements that facilitate determining the victim's health state. Other parameters/sensors than the ones listed here could be used, i.e. the types of parameters and sensors are not limited to the ones described above. Blood perfusion sensor 107 provides the measured values of a physiological parameter related to blood perfusion to an operating parameter adjuster 108. Operating parameter adjuster 108 has another input that receives a signal from an actuator driver 110 and will be explained in the context of Fig. 2. Operating parameter adjuster 108 provides two outputs on connections 109 and 115 to the actuator driver 110. Connection 109 goes to a section of the actuator driver 110 in which operating parameters are stored, such as for example the gains of a PID controller that is part of controller 112. The exchange of information between the memory/storage 114 for operating parameters and the controller 112 is indicated by a dotted arrow. The other connection from operating parameter adjuster 108 to the actuator driver 110 leads to a memory/storage 113 in which the desired waveform ya(t) is stored. Accordingly, in this embodiment the desired compression waveform can be adjusted by the operating parameter adjuster, as well. However, this is not required for performing the invention.

Fig. 2 shows a more detailed view of operating parameter adjuster 108. From actuator driver 110 the operating parameter adjuster 108 receives a signal indicating the execution of a new compression. Within operating parameter adjuster this signal is conducted to a counter 230 (CNTR). Another input to operating adjuster 108 is provided by blood perfusion sensor 107 as already described in the context of Fig. 1. Operating parameter adjuster 108 comprises a memory/storage MEM in which data relating to previous compression cycles are stored. In the embodiment shown in Fig. 2, the data is organized in the form of a table having a column for the number of the compression count CNT. This column is fed by the compression cycle counter 230. The current compression cycle is indicated by the letter i, whereas previous compression cycles are indicated by i-1, i-2, i-3 and so forth. Instead of counting each compression cycle it may be envisaged to group several compression cycles having identical operating parameter settings. Another column (or group of columns) labeled OP PAR of the table contains the operating parameters that were used during the corresponding compression cycle. A third column (or group of columns) labeled PFSN DATA for perfusion data contains measured values relative to the blood perfusion that was observed during the compression cycle. The third column (or group of columns) may also contain average values of the measured values and/or measurements corresponding to other physiological parameters besides those that are blood perfusion related.

The operating parameter adjuster further comprises a tendency analyzer 240 and an evaluator 260. The tendency analyzer 240 receives values from the table in memory MEM corresponding to previous compression cycles. In particular, tendency analyzer 240 receives values from a section 271 of the table, in which previous operating parameters are stored, and from a section 274, in which previous measurements of blood perfusion are stored. Tendency analyzer 240 determines how the blood perfusion measurements react to changes of the operating parameters, in particular whether blood perfusion has improved or degraded due to a modification of one or several of the operating parameters. Tendency analyzer may create and/or populate a characteristics map.

Tendency analyzer may comprise a module that is capable of calculating a cost function taking the measured values of perfusion data as arguments. The following cost function S is proposed for two physiology parameters A and B, extension to more parameters is straightforward (this function is used for example only, other cost function may be used, they are included in the claims).

_ _ττr AA _ττr AB _ττr AA AB

S = W, + W₂ + W_n

S Al₀ D R_Q / AI₀ DK₀

Here ΔA = A(p) -Ao and ΔB = B(p) -Bo where Ao and Bo are target values for the parameters A and B. A(p) and B(p) are the (average) values of A and B after n (say 30 compressions and measurement number p, W_n and W_nm are (user defined) weight factors for the different parameters and the interaction terms of these parameters. The weight factors and set values can be obtained either from evidence based medical research or can be set by the user. For optimization S has to be maximized. The evaluator 260 receives the result of the tendency analysis from tendency analyzer 240. Based on this knowledge, evaluator 260 attempts to find the optimal settings for the operating parameters. Evaluator 260 also exchanges information with an operating parameter limiter 250 that defines admissible ranges for the operating parameters. If evaluator 260 determines a setting for an operating parameter that is outside of reasonable and/or safe values as informed by operating parameter limiter 250, then evaluator 260 will reevaluate or simply lower the setting to a value that is admissible. Operating parameter limiter 250 may also define limits for groups of parameters in order to exclude harmful or unwanted combinations of operating parameters. Finally, operating parameter limiter may also take into account the measurements of the physiological parameters related to blood flow or other physiological measurements in order to define stricter or more relaxed limits for the operating parameters.

The operating parameters determined by evaluator 260 are transmitted to the memory 114 for operating parameters of the actuator driver 110. If applicable, a desired waveform ya determined by the evaluator 260 is transmitted to the memory 113 for the desired waveform within actuator driver 110. The operating parameters determined by evaluator 260 are also transmitted to the memory MEM in operating parameter adjuster 108 to be stored in section 272 of the table. A field 273 of the table is populated with measurement data relative to blood perfusion. When the next compression cycle is started, the operating parameters and the measurement data in fields 272 and 273 are moved from line i to line i-1 in order to be available as previous operating parameters and measurements.

Fig. 3 shows a flow chart of a method for automated cardio pulmonary resuscitation according to a first aspect of the invention. The method starts in block 301. In block 302 the operating parameters are set to safe initial values. At least one chest compression is performed in block 303 and measured values relative to blood perfusion are collected during the execution of block 304. In block 305 the operating parameters are modified to new settings. Next, the measurements are evaluated and optimal settings are determined in block 306. At branching point 307 it is determined, whether cardio pulmonary resuscitation should be continued or terminated according to a user input. The default condition for the loop is to continue unless the user enters an input that indicates that the method should be terminated. If cardio pulmonary resuscitation is to be continued, the method branches back to block 303. If cardio pulmonary resuscitation is to be terminated, the method ends in block 312. Fig. 4 shows a flow chart of a method for automated cardio pulmonary resuscitation according to a second aspect of the present invention. The method starts in block 401. In initializing block 402 the operating parameters are set to safe initial values and a counter variable is set to N = 1. Counter variable N relates to the set of operating parameters, such as compression depth, rise time, hold time, fall time, duty cycle etc. In block 403 at least one chest compression is performed. Measured values relative to blood perfusion, such as ETCO₂ and CBF, are collected and compared with previous values in block 404. A cost function S(p) for the current iteration p is calculated in block 405 using the measured values as arguments. A previous result of calculating the cost function S(p-1) is retrieved and the difference ΔS = S(p) - S(p-l) is determined in block 406. At a branching point 407 a determination is made whether the difference ΔS of operating parameter in the cost function S is greater than a threshold ε (epsilon): "ΔS > ε ?". The threshold ε means that changes in the cost function that are larger than ε are considered to be significant changes, i.e. improvements. If the result of the determination within branching point 407 is yes (Y), then the method continues at a second branching point 408 where operating parameter N (e.g. the compression depth) is changed, and more particularly usually increased. If the determination at branching point 407 is negative (N), then optionally the operating parameter is reset to its previous setting. The counter variable N is then increased to N+l, which means that the next operating parameter (e.g. compression rate) will be the object of the next optimization iteration. At branching point 410 it is checked, whether an operating parameter with the number N exists. If not (exit "N" of branching point 410) the method has cycled through all operating parameters and starts over with the first operating parameter N=I, cf. block 412. If there is an operating parameter with the number N, the method continues at block 411 where operating parameter N is changed (usually increased). From both blocks 411 and 412 the method continues to a branching point 413 at which a determination is made whether cardio pulmonary resuscitation should be ended or continued. If cardio pulmonary resuscitation should be ended (e.g. due to a user interaction) then the method stops at block 415. Otherwise continues at block 403 at which the iteration counter p is increased.

Fig. 5 shows the scheduling of various measurements of physiological parameters. The end-tidal CO₂ pressure ETCO₂ is used as the physiology parameter of interest. The target value Ao is 35 mmHg. Meaningful ETCO₂ can only be obtained during the ventilation phase (more precisely the expiration phase during the ventilation) of cardio pulmonary resuscitation, in this case after 30 compressions (i.e. roughly 20 seconds). Hence the second feedback loop cannot be instantaneous. The 30 compressions are also needed to obtain relevant data, as response time to changes in cardio pulmonary resuscitation can be long.

The ETCO₂ parameter can be optimized by maximizing the cost function S for various CPR parameters, a (not complete) list includes compression depth (force), compression frequency and shape (i.e. slope) and duty cycle of the compression pulse for a fixed frequency. It is important to note that the servo loop guarantees reproducible and consistent compression pulses so that variations in pulses are negligible and well defined.

In this example three pulse parameters are varied, the compression depth, frequency, and pulse rise time. Many other variations are possible, as well. As a compression waveform a trapezium like type pulse with a rise time of 200ms, a time at maximum compression of 100ms, and a fall time of 100ms are chosen as start values, the pulse time

0.67 seconds (90 per minute). The initial depth is 3.8 cm. After the first 30 compressions (30 x CMPR) ETCO₂ is recorded during the ventilation and S is evaluated (Wi=I for this case). Next the compression pulse form is maintained but the maximum compression depth is increased with a certain step (take 0.5 cm as an example). After the second run (p=2) of 30 compressions ETCO₂ is measured again during the ventilation phase (2 x VNTL), in case of a significant increase of S (ΔS > ε) the compression depth is increased by 0.5 cm again, in case of a significant decrease or in case of non significant increase (less thorax damage expected) the old value of 3.8 cm is used again. After 30 compressions ETCO₂ is determined again, for the 4.8 cm depth pulse a decrease in ETCO₂ indicates that the old value of 4.3 cm is to be used again, in case of an increase the compression depth is increased to its maximum value. After the optimum depth has been achieved, the next parameter (frequency, hold time, and rise time) can be optimized in the same way.

A remark to be made is that the ETCO₂ parameter may decrease strongly when vaso-compressors (i.e. nor-adrenaline, ...) are administered. In this case the optimization has to be stopped and the procedure is restarted because the previous data has become meaningless. It is still important to continue since the effort is to obtain the best possible value for ETCO₂ for the specific patient rather than some predetermined value. A new phase in the resuscitation is reached and optimization could continue from the present settings. Restart of the optimization could be triggered by user input, via an input device, i.e. button, touch-sensitive display, microphone etc. The user may choose from a mark event list, i.e. drug delivery or a certain treatment.

A decrease in ETCO₂ may be observed after the optimum settings have been obtained, for example because the patient deteriorates. In case the maximum settings have not been reached they may be increased. In case the maximum settings were reached or no improvement is detected, a warning is given to the responder.

Instead of varying one parameter at the time, a cost function based approach (change two or more parameters at the same time) can be used. This may be a preferred method as interactions between the parameters may become apparent. Figures 6 to 9 show different types of dependencies of a pair of two physiological parameters from an operating parameter OPl. The two physiological parameters may be for example the end-tidal CO₂ pressure ETCO₂ (A, circles in Figs. 6 to 9) and the carotid blood flow CBF (B, crosses in Figs. 6 to 9). The carotid blood flow is representative for the brain perfusion. A parameter related to the net CBF is measured with an ultra- sound probe in a CW Doppler mode at the carotid artery. From the spectrogram the maximum flow velocity is determined as a function of time. The integral of the net maximum velocity over a compression pulse is the parameter B. It is known that depending on the CPR parameters either the perfusion of the heart or brain is favored (i.e. there may not be a common optimum for the two physiological parameters). Carotid blood flow is measured at the end of 30 compressions (say average of last five compressions: cf. CBF AVG LAST 5). Set values for A and B are 35 mmHg and +2 cm/s respectively. Measuring the flow velocity serves as a measure for the actual flow rate.

When two physiology parameters are measured, the cost function S is evaluated using the two parameters A and B at measurement cycle p (the interaction term W₁₂ is here set to 0, Wi = 0.5 and W₂ = 1.0). In case of an increase or decrease in S a similar procedure as described above is used.

In case both physiological parameters ETCO₂ and CBF show a parallel behavior (Figures 6 and 7), the procedure is substantially as in the embodiment having only one physiological parameter. In the case of Figures 8 and 9 however, the two physiological parameters ETCO₂ and CBF depend on the operating parameter OPl in an opposite manner, i.e. ETCO₂ increases and CBF decreases with increasing values of operating parameter OPl (Fig. 8) and vice versa (Fig. 9). In case of the carotid blood flow CBF being too low (either initially or finally) the choice should favor the highest CBF. This choice is, however, subject to user preferences. If carotid blood flow is favored, then in Fig. 8 the value of operating parameter OPl would be chosen close to the upper end of its admissible range, i.e. substantially towards the right end of the diagram in Fig. 8. In Fig. 9 on the other hand, the value of operating parameter OPl would be chosen to be closer to the lower end of the admissible range, i.e. more to the left of the diagram in Fig. 9. The weight of the interaction term Wi₂ in the cost function can also be used to govern the behavior of an automated cardio pulmonary resuscitation apparatus in the case of two diverging physiology parameters. This is useful, when there is no preference for one of the physiology parameters. In the event the two physiology parameters diverge, the interaction term

Λ ^o becomes negative, because ΔA and ΔB have opposite signs. Thus, the result of the cost function is attenuated so that the operating parameter(s) remain more constant.

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. For example, it is possible to operate the invention in an embodiment wherein an invasive sensor is used.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor 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 measured cannot be used to advantage. A computer program may be stored/distributed on a suitable 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. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. Automated Cardio Pulmonary Resuscitation apparatus, comprising a chest compression actuator (102), an actuator driver (110) that supplies time- varying drive signals to the chest compression actuator (102) in dependence of operating parameters of the actuator driver, - a physiological parameter sensor (107) supplying measured values of a physiological parameter related to blood perfusion, an operating parameter adjuster (108) that uses the measured values for optimizing blood perfusion by consecutively modifying the operating parameters to new settings and evaluating for which one of the settings the measured value related to blood perfusion is optimal.

2. Automated Cardio Pulmonary Resuscitation apparatus according to claim 1, wherein the actuator driver (110) comprises an inner control loop that comprises: a sensor (106) for a parameter related to chest compression, the sensor supplying a chest compression measurement, an inner loop controller (112) receiving the chest compression measurement and performing closed loop control on the chest compression actuator (102) in accordance with a desired chest compression waveform, wherein the operating parameters comprise control settings of the inner loop controller (112) and/or of the desired chest compression waveform.

3. Automated Cardio Pulmonary Resuscitation apparatus according to claim 2, further comprising an outer control loop that comprises the physiological parameter sensor (107) and the operation parameter adjuster (108).

4. Automated Cardio Pulmonary Resuscitation apparatus according to claim 1, wherein the operating parameter adjuster (108) comprises a compression counter (230), a memory (MEM) storing past and present records of operating parameters and associated measured values after a predetermined number of compressions, a tendency analyzer (240) using the measured values, and an evaluator (260) using a result of the tendency analyzer (240) for a decision as to increase, decrease, or maintain a particular operating parameter.

5. Automated Cardio Pulmonary Resuscitation apparatus according to claim 4, wherein the tendency analyzer (240) is capable of detecting abnormal variations in the measured values and outputting a corresponding indication, and wherein the evaluator (260) uses the indication to restart from default values.

6. Automated Cardio Pulmonary Resuscitation apparatus according to claim 4, wherein the evaluator (260) selects a first setting instead of a second setting, if the first setting causes less expected thorax damage than a second setting, and if the measured values corresponding to the first setting are only insignificantly less optimal than the measured values corresponding to the second setting.

7. Automated Cardio Pulmonary Resuscitation apparatus according to claim 1, further comprising a second physiological parameter sensor (270) supplying second measured values for a second physiological parameter related to blood perfusion of the brain, wherein the operating parameter adjuster (108) is prioritized to optimize the operating parameters so as to maximize the blood perfusion of the brain.

8. Method for Automated Cardio Pulmonary Resuscitation, comprising: a) setting operating parameters of an automated Cardio Pulmonary Resuscitation apparatus to safe initial values, b) the automated Cardio Pulmonary Resuscitation apparatus performing at least one chest compression, c) collecting a measured value of a blood perfusion related physiological parameter, d) evaluating the measured value with respect to compliance with predetermined conditions, e) modifying the operating parameters to new settings, and f) evaluating for which one of the settings the measured value related to blood perfusion is optimal.

9. Method according to claim 8, further comprising: setting a desired waveform, collecting chest compression measurements, - performing closed loop control on a chest compression actuator (102) within an inner control loop so that the chest compression measurements substantially fit the desired waveform.

10. Method according to claim 8, further comprising performing outer loop control based on the measured value of the blood perfusion related physiological parameter.

11. Method according to claim 8, wherein the method further comprises: el) increasing the operating parameter by a certain step, e2) performing further chest compressions with the increased operating parameter, e3) collecting a new measured value of the blood perfusion related physiological parameter and determining a variation compared to the previously collected measured value, fl) comparing the variation to a predetermined threshold, f2) increasing, decreasing, or maintaining the operating parameter in dependence of a result of comparing.

12. Method according to claim 8, further comprising: cl) collecting a second measured value of a second physiological parameter related to blood perfusion of the brain,

O) evaluating whether a variation of the second measured value shows the same tendency, in terms of improvement, as a variation of the measured value, f4) in case of divergent tendencies, prioritizing the second physiological parameter and selecting a brain perfusion oriented setting among the settings so that blood perfusion of the brain is favored.

13. Computer program enabling a processor to carry out the method of claim 8.

14. Signal transmitted from a physiological parameter sensor (107) to an operating parameter adjuster (108) of an automated Cardio Pulmonary Resuscitation apparatus, the physiological parameter sensor supplying measured values of a physiological parameter related to blood perfusion.