DEFIBRILLATOR DISPLAY

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application Serial No. 61/304  119  filed on February 12  2010  entitled "DEFIBRILLATOR CHARGING " and U.S. Provisional Application Serial No. 61/307 690  filed on February 24  2010  entitled "DEFIBRILLATOR DISPLAY " the entire contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

This document relates to cardiac resuscitation  and in particular to systems and techniques for assisting rescuers in performing cardio-pulmonary resuscitation (CPR).

BACKGROUND

The heart relies on an organized sequence of electrical impulses to beat effectively. Deviations from this normal sequence is known as "arrhythmia." Certain medical devices include signal processing software that analyzes electrocardiography (ECG) signals acquired from a medical patient (e.g.  a victim at a scene of an emergency) to determine when a cardiac arrhythmia such as ventricular fibrillation (VF) or shockable ventricular tachycardia (VT) exists. These devices include automated external defibrillators (AEDs)  ECG rhythm classifiers  and ventricular arrhythmia detectors. An AED is a defibrillator - a device that delivers controlled electrical shock to a patient - while being relatively easy to use  such as by providing verbal prompts to a provider of care to "talk" the provider through a process of evaluating a patient for  attaching the patient to  and activating  AED therapy. Certain of the medical devices just discussed are also capable of recognizing the two distinct cardiac waveforms: VT and VF.

VT is a tachydysrhythmia that originates from a ventricular ectopic focus  characterized by a rate that is typically greater than 120 beats per minute and wide QRS complexes. VT may be monomorphic (typically regular rhythm originating from a single focus with identical QRS complexes) or polymorphic (unstable  may be irregular rhythm  with varying QRS complexes). An example rhythm for an unstable VT is illustrated in FIG. 1A. Depending on the rate and the length of time that the VT has been sustained  a heart in the VT state may or may not produce a pulse (i.e.  pulsatile movement of blood through the circulatory system). The cardiac activity in the VT state still has some sense of organization (note that the "loops" are all basically the same size and shape). If there is no pulse associated with this VT rhythm  then the VT is considered to be unstable and a life threatening condition. An unstable VT can be treated with an electrical shock or defibrillation.

Supraventricular tachycardia (SVT) is a rapid heartbeat that begins above the heart""s lower chambers (the ventricles). SVT is an abnormally fast heart rhythm that begins in one of the upper chambers of the heart (atria)  a component of the heart""s electrical conduction system called the atrioventricular (AV) node  or both. Although SVT is rarely life-threatening  its symptoms  which include a feeling of a racing heart  fluttering or pounding in the chest or extra heartbeats (palpitations)  or dizziness can be uncomfortable.

VF is usually an immediate life threat. VF is a pulseless arrhythmia with irregular and chaotic electrical activity and ventricular contraction in which the heart immediately loses its ability to function as a pump. VF is the primary cause of sudden cardiac death (SCD). An example rhythm for VF is illustrated in FIG. IB. This waveform does not have a pulse associated with it. There is no organization to this rhythm (note the irregular size and shape of the loops). The pumping part of the heart is quivering like a bag of worms  and it is highly unlikely that this activity will move any blood. The corrective action for this rhythm is to defibrillate the heart using an electrical charge.

A normal heart beat wave starts at the sinoatrial node (SA node) and progresses toward the far lower corner of the left ventricle. A massive electrical shock to the heart can correct the VF and unstable VT rhythms. This massive electrical shock can force all the cardiac cells in the heart to depolarize at the same time. Subsequently  all of the cardiac cells go into a short resting period. The hope is that the sinoatrial node (SA node) will recover from this shock before any of the other cells  and that the resulting rhythm will be a pulse-producing rhythm  if not normal sinus rhythm.

Many AEDs implement algorithms to recognize the VT and VF waveforms by performing ECG analyses at specific times during a rescue event of a patient using defibrillation and cardio-pulmonary resuscitation (CPR). The first ECG analysis is usually initiated within a few seconds after the defibrillation electrodes are attached to the patient. Subsequent ECG analyses may or may not be initiated  based upon the results of the first analysis. Typically  if the first analysis detects a shockable rhythm  the rescuer is advised to deliver a defibrillation shock. Following the shock delivery  a second analysis can be initiated automatically to determine whether the defibrillation treatment was successful or not (i.e.  the shockable ECG rhythm has been converted to a normal or other non-shockable rhythm). If this second analysis detects the continuing presence of a shockable arrhythmia  the AED advises the user to deliver a second defibrillation treatment. A third ECG analysis may then be executed to determine whether the second shock was or was not effective. If a shockable rhythm persists  the rescuer is then advised to deliver a third defibrillation treatment.

Following the third defibrillator shock or when any of the analyses described above detects a non-shockable rhythm  treatment protocols recommended by the American Heart Association and European Resuscitation Council require the rescuer to check the patient""s pulse or to evaluate the patient for signs of circulation. If no pulse or signs of circulation are present  the rescuer can be directed to perform CPR on the victim for a period of one or more minutes. The CPR includes rescue breathing and chest compressions. Following this period of CPR  the AED reinitiates a series of up to three additional ECG analyses interspersed with appropriate defibrillation treatments as described above. The sequence of three ECG analyses/defibrillation shocks followed by 1 - 3 minutes of CPR  continues in a repetitive fashion for as long as the AED""s power is turned on and the patient is connected to the AED device. Typically  the AED provides audio prompts to inform the rescuer when analyses are about to begin  what the analysis results were  and when to start and stop the delivery of CPR.

Many studies have reported that the discontinuation of precordial compression can significantly reduce the recovery rate of spontaneous circulation and 24-hour survival rate for victims. Thus  it is useful to recognize abnormal heart rhythms during chest compressions. There is recent clinical evidence showing that performing chest compressions before defibrillating the patient under some circumstances can be

beneficial. Specifically  it is clinically beneficial to treat a patient with chest compressions before defibrillation if the response times of the medical emergency system result in a delay of more than four minutes  such that the patient is in cardiac arrest for more than four minutes. Chest compression artifact rejection can employ spectral analysis of the ECG  defibrillation success prediction  and therapeutic decisionmaking typically specify a set of parameters in the ECG frequency spectrum to be detected. For example  US 5 683 424 compares a centroid or a median frequency or a peak power frequency from a calculated frequency spectrum of the ECG to thresholds to determine if a defibrillating shock is necessary.

Unfortunately  existing AEDs require batteries able to deliver large amounts of current due to the charging requirements of defibrillator high voltage capacitors. This results in batteries that are excessive in both size and weight that limit both their portability  convenience  and in the case of external  wearable defibrillators such as the Life Vest (ZOLL Medical  Chelmsford  MA) their wearability and comfort. In addition  batteries continue to be the least reliable element of the AEDs currently manufactured  with regular recalls resulting from manufacturing defects as well as normal end-of-life degradation that always occurs with batteries  but are particularly troublesome for life-saving equipment.

SUMMARY

This document describes systems and techniques that may be used to provide information about patient status during the use of a defibrillator device. The systems and techniques described herein aim to identify the most important data and to display the information in an efficient and effective manner to a rescuer. The data displayed to the rescuer can change based on the actions of the rescuer. For example  the data displayed can differ based on whether the rescuer is currently administering CPR chest compressions to the patient. The data about the patient is presented graphically and textually in a manner that improves the ability of a rescuer to quickly understand the state of a patient and to make clinical decisions that will benefit the patient. For example  during CPR chest compressions  information about the chest compressions including rate and depth is displayed on the same display device as a filtered ECG waveform and C02 or Sp02 waveform. The display of such information in one

location provides the advantage of giving the rescuer needed information about the patient in one convenient location in an easy to view formal. In certain

implementations  additional information about the quality of the CPR chest compressions can be presented to the rescuer such as a release indicator.

In certain implementations  such systems and technique may provide one or more advantages. For example  patient care may be improved when a rescuer can easily view well-formatted information in a single location. Also  rescuers may be able to modify their administration of CPR to be more effective because they have been presented relevant data in an understandable manner.

In one implementation  a method for monitoring patient activity using an external defibrillator includes obtaining data regarding chest compressions performed on the patient  determining values for depth and rate of a plurality of the chest compressions  and displaying on a graphical display screen of the defibrillator  indications of the determined values for depth and rate.

Embodiments can include one or more of the following.

Determining the values for depth and rate can include determining numeric values in terms of distance for depth and compressions per minute for rate  and wherein displaying the indications of the determined values for depth and rate comprises displaying numbers that correspond to the determined numeric values.

The method can also include displaying an icon adjacent the indications of the determined values that indicates whether the chest compressions are being performed properly. A color of the icon can change based on whether the chest compressions are being performed properly or improperly.

The method can also include receiving information about the patient""s heart activity and displaying on the graphical display  with the determined values for depth and rate  an electrocardiogram of the patient. Displaying the electrocardiogram can include moving an electrocardiogram trace laterally across the display. The method can also include displaying an unfiltered electrocardiogram  sensing that chest compressions have commenced on the patient  and subsequently displaying a filtered electrocardiogram. The method can also include momentarily displaying on a trace of the electrocardiogram  an unfiltered portion showing compression artifacts  between another unfiltered portion and a filtered portion.

The method can also include displaying second data from the patient in coordination with the electrocardiogram. The method can also include changing a source of the second data in response to sensing that chest compressions have commenced on the patient. Changing the source of the second data can include changing from SP02 to C02. Changing the source of the second data can include changing from a patient chemical measurement to a chest compression measurement. The chest compression measurement can be displayed in the form of a bar graph. Lengths of bars in the bar graph can represent compression depths and spacing of bars in the bar graph represent compression rate. The method can also include displaying indicators for standard depth and rate with the bar graph.

Obtaining the data regarding chest compressions performed on the patient can include obtaining measurements from an accelerometer that is positioned to move in coordination with the patient""s breastbone. Determining a value for depth can include double integrating measurements from the accelerometer. The accelerometer can be attached to a housing that is in turn attached to a pair of defibrillator electrodes to be placed on the patient.

In another implementation  an external defibrillator includes one or more sensors arranged to contact a patient and obtain measurements regarding chest compressions performed on the patient  a video display screen for displaying graphical representations regarding status of the patient and the defibrillator to a rescuer  and a processor connected to memory that stores computer instructions for determining values of depth and rate of chest compressions performed on the patient and sensed by the sensors  and causing the video display screen to display indications of the determined values for depth and rate.

Embodiments can include one or more of the following.

The instructions for determining the values for depth and rate can include instructions for determining numeric values in terms of distance for depth and compressions per minute for rate  and wherein displaying the indications of the determined values for depth and rate comprises displaying numbers that correspond to the determined numeric values. The instructions can be further provided to cause the video display screen to display an icon adjacent the indications of the determined values that indicates whether the chest compressions are being performed properly. A color of the icon changes based on whether the chest compressions are being performed properly or improperly.

The instructions can be further provided to cause the display on the video display screen an electrocardiogram of the patient with the determined values for depth and rate  in response to receiving information about the patient""s heart activity.

Displaying the electrocardiogram can include moving an electrocardiogram trace laterally across the display. The instructions can be further provided to cause the display on the video display screen of an unfiltered electrocardiogram  and the subsequent display of a filtered electrocardiogram upon sensing that chest

compressions have commenced on the patient. The instructions can be further provided to momentarily display on a trace of the electrocardiogram  an unfiltered portion showing compression artifacts  between another unfiltered portion and a filtered portion. The instructions can be further provided to display second data from the patient in coordination with the electrocardiogram. The instructions can be further provided to change a source of the second data in response to sensing that chest compressions have commenced on the patient. Changing the source of the second data can include changing from SP02 to C02. Changing the source of the second data can include changing from a patient chemical measurement to a chest compression measurement.

The chest compression measurement can be displayed in the form of a bar graph. Lengths of bars in the bar graph can represent compression depths and spacing of bars in the bar graph represent compression rate. The instructions can further be provided to display indicators for standard depth and rate with the bar graph. Obtaining the data regarding chest compressions performed on the patient can include obtaining measurements from an accelerometer that is positioned to move in coordination with the patient""s breastbone. Determining a value for depth can include double integrating measurements from the accelerometer.

The one or more sensors can include an accelerometer that is attached to a housing that is in turn attached to a pair of defibrillator electrodes to be placed on the patient.

In one implementation  an external defibrillator includes one or more sensors arranged to contact a patient and obtain measurements regarding chest compressions performed on the patient  a video display screen for displaying graphical

representations regarding status of the patient and the defibrillator to a rescuer  and means for determining values of depth and rate of the chest compressions and for causing the video display screen to display indications of the determined values for depth and rate in response to receiving data from the one or more sensors that indicates the depth and rate of the chest compressions.

Other features and advantages will be apparent from the description and drawings  and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a magnitude versus time plot of a ventricular tachycardia (VT) rhythm.

FIG. IB is a magnitude versus time plot of a ventricular fibrillation (VF) rhythm.

FIG. 2 is a diagram of one implementation including an automatic electronic defibrillator (AED) and a multiple lead electrocardiograph (ECG) device.

FIG. 2A is a diagram of the AED of FIG. 2.

FIGS. 3A and 3B are examples of ECG analysis and charging cycles.

FIG. 4A is a flow chart showing actions taken to charge a defibrillation device during chest compressions associated with a CPR interval.

FIG. 4B is a flow chart showing actions taken to charge a defibrillation device using different current levels that are selected based on the likelihood of a shockable rhythm being observed.

FIG. 4C is a flow chart showing actions taken to adaptively charge a defibrillation device using different current levels based on the likelihood of a shockable rhythm being observed..

FIG. 4D is a flow chart showing actions taken to adaptively charge a defibrillation device to a level selected based on ECG analysis.

FIG. 5A is a diagram of and ECG signal.

FIG. 5B is a diagram of a CPR acceleration signal showing strong cross-correlation with the ECG signal.

FIG. 6A is a diagram of and ECG signal.

FIG. 6B is a diagram of a CPR acceleration signal showing low cross-correlation with the ECG signal.

FIG. 7 is a diagram of a defibrillation device with a display.

FIG. 8A is a flow chart showing actions taken to modify information presented on a display of a defibrillation device based on the detection of CPR chest compressions.

FIGS. 8B-8E are screenshots showing exemplary information presented on a defibrillator display.

FIG. 9A is a flow chart showing actions taken to provide an indication of CPR quality on a display of a defibrillator device.

FIGS. 9B and 9C are screenshots showing exemplary information presented on a defibrillator display.

FIG. 10A is a flow chart showing actions taken to provide a release indicator.

FIGS. 10B and IOC are screenshots showing exemplary information presented on a defibrillator display.

FIG. 11 is a screenshot showing exemplary information presented on a defibrillator display.

DETAILED DESCRIPTION

This description discusses systems and techniques for providing defibrillation energy in a controlled manner. In general  such energy needs to be built up  such as by charging a capacitor  and that build up of energy may take an appreciable length of time. Using the techniques discussed here  a system can analyze a patient""s needs in advance of the time to delivery defibrillation pulse (e.g.  while a rescuer is performing chest compressions) and can begin charging a capacitor or other appropriate energy delivery mechanism sufficiently in advance of the time that a shock will be needed  so that the shock can be delivered as soon as it is needed.

Referring now to FIG. 2  an AED 10 is shown that may be used to provide a defibrillation shock at an appropriate time. In the figure  which shows an example implementation  a rescuer uses an AED 10 to automatically monitor a victim during cardiac resuscitation. The AED 10 uses measured ECG signals to monitor the victim""s heart  and charges the defibrillation device within the AED while the victim is resuscitated using chest compressions techniques. In some examples  the manner in which the defibrillation device is charged (e.g.  the rate of charge  the total amount of charge stored) can be based on the measured ECG signals. Advantageously  charging the defibrillation device during CPR chest compressions reduces the amount of time that the victim is not receiving chest compressions because  if a shockable rhythm exists  the device is armed and ready to deliver the shock as soon as the rescuer completes the chest compressions.

The AED 10 includes a speaker 16  a display screen 18  an analog-to-digital converter 20  a processor 22  and a defibrillator pulse generator 24. The analog-to-digital converter 20 is connected to a set of ECG leads that are in turn attached to the victim. The ECG leads pass signals to the processor 22 for monitoring the electrical rhythms of the victim""s heart. The converter 20 sends the signals from the ECG leads to the processor 22. The processor 22 monitors the victim""s heart for dangerous rhythms using the ECG signals while the victim is resuscitated using chest

compressions techniques.

If the AED 10 detects a dangerous heart rhythm  the AED 10 generates an alarm signal. The alarm signal is noticeable to the rescuer. The AED 10 can generate a defibrillating shock to the victim when the rescuer issues a command to the AED 10 directing such a shock. The defibrillating shock is intended to remedy the dangerous rhythm of the victim""s heart.

The AED 10 also includes a charging module 19 that is configured to charge the AED during chest compressions. The module 19 can adaptively charge the AED based on monitored ECG signals. In some examples  the defibrillator is pre-charged only if a shockable rhythm is likely to exist as determined by analysis of the monitored ECG signals. In some additional examples  the level of charge for the device is determined and set based on the monitored ECG signals. In some additional examples  the method of charging (e.g.  the rate of charge) varies based on the monitored ECG signals in an effort to conserve power. For example  if time allows  a capacitor may be charged more slowly than it normally would in order to conserve power  but still ensure that the capacitor will reach its full charge just as the defibrillator is needed by the rescuer.

The AED 10 uses a rhythm advisory method for a) quantifying the frequency-domain features of the ECG signals; b) differentiating normal and abnormal ECG rhythms  such as VF; c) detecting the onset of abnormal ECG rhythms; and d) making decisions about the physiological states of the heart. This frequency-domain measure can be reliable with or without the presence of the chest compression artifact in the ECG signals. The AED 10  after identifying the current physiological state of the heart  can make a decision about appropriate therapeutic action for the rescuer to make and communicate the action to the rescuer using the speaker 16 and the display screen 18.

The AED 10 may incorporate functionality for performing additional therapeutic actions such as chest compressions  ventilations  or delivery of intravenous solution-containing metabolic or constitutive nutrients. Based on the results of the analysis of the rhythm advisory method  the AED 10 may automatically deliver the appropriate therapy to the patient.

The AED 10 may also be configured in "advisory" mode wherein the AED 10 will prompt the caregiver after the AED 10 has made a determination of the best therapy  and acknowledgement by the caregiver/device operator  in the form of a button press or voice-detected acknowledgement  is required before therapy is delivered to the patient.

The AED 10 analyzes the ECG signals to predict defibrillation success as well as to decide whether it is appropriate to defibrillate or to deliver an alternative therapy such as chest compressions  drugs such as epinephrine  constitutive nutrients such as glucose  or other electrical therapy such as pacing.

In some examples  one or more therapeutic delivery devices 30 automatically deliver the appropriate therapy to the patient. The therapeutic delivery devices 30 can be  for example  a portable chest compression device  a drug infusion device  a ventilator and/or a device that includes multiple therapies such as defibrillation  chest compression  ventilation and drug infusion. The therapeutic delivery devices 30 are physically separate from the defibrillator AED 10  and control of the therapeutic delivery devices 30 may be accomplished by a communications link 32. The

communications link 32 may take the form of a cable but preferably the link 32 is via a wireless protocol.

In other examples  control and coordination for the overall resuscitation event and the delivery of the various therapies may be accomplished by a device 34 or processing element that is external to the AED 10. For instance  the device 34 may download and process the ECG data from the AED 10; analyze the ECG signals  perform relevant determinations like those discussed above and below based on the analysis  and control the other therapeutic devices 30  including the AED 10. In other examples  the AED 10 may perform all the processing of the ECG  including analyzing the ECG signals  and may transmit to the control device 34 only the final determination of the appropriate therapy  whereupon the control device 34 would perform the control actions on the other linked devices 30.

Chest compression artifacts can be separated from the ECG signal components  making it possible for the AED 10 to process the ECG signal without halting the processing during chest compressions. Exemplary methods for analyzing the ECG signal to determine if a shockable rhythm exists are described  for example  in U.S. Patent 7 565  194  titled "ECG Rhythm Advisory Method " the contents of which are hereby incorporated by reference in their entirety.

It has been recognized that good chest compressions during CPR is essential to saving more victims of cardiac arrest. The compression rate recommended by the American Heart Association in its guidelines is greater than 100 compressions per minute. Many studies have reported that the discontinuation of chest compressions  such as is commonly done for ECG analysis and charging of a defibrillator  can significantly reduce the recovery rate of spontaneous circulation and 24-hour survival rate. Because of safety issues with delivery of a high voltage defibrillation shocks with voltages of 1000 - 2000 volts  rescuers are taught to cease chest compressions and remove their hands from the victim""s chest before initiating the defibrillation shock. By analyzing ECG signals during chest compressions as a mechanisms to permit earlier charging of an energy delivery device (e.g.  a capacitor) in a defibrillator device  the gaps in providing chest compressions can be reduced  and patient care increased.

FIG. 3 A shows an example of an ECG analysis and charging cycle in which charging of a defibrillator device starts after a CPR interval has ended. As shown in the figure  in operation of some AED devices  the rescuer is instructed to perform chest compressions for a two minute CPR interval 300 after which the rescuer is instructed to pause his or her performance of CPR 304. At this point  the rescuer removes his or her hands from the victim  ECG analysis is performed  and the defibrillator device is charged (interval 302). As such  a time period elapses (time period 302) during which the rescuer is not delivering chest compressions to the victim. This elapsed time period before delivery of the shock 307 can be  for example  about 10 seconds— of which a portion is devoted to performing the ECG analysis and a portion is devoted to charging the defibrillation device. While methods exist for processing ECG signals without halting the processing during CPR chest compressions  a time period may still elapse between the cessation of chest compressions and availability of an adequate charge for delivering a shock.

FIG. 3B shows an example of an ECG analysis and charging cycle in which charging of a defibrillator device starts before a CPR interval has ended. The CPR interval can be based on a length of time of administration of chest compressions (e.g.  as shown in FIG. 3B)  a total number of chest compressions  a total number of effective chest compressions based on depth or rate of the compression  a total length of time of effective chest compressions  or can be variable based on one or more observed factors such as the ECG analysis. The CPR interval can additionally be updated by software or firmware to handle different CPR protocols such that the device is charged and the defibrillation therapy is delivered according to the protocol. As shown in the figure  in operation methods described herein  the defibrillation device is charged while the rescuer is providing the CPR chest compressions. Similar to the method described with respect to FIG. 3A  the rescuer is instructed to perform chest compressions for a two minute CPR interval 308. During the two minute CPR interval  ECG analysis is performed and the defibrillator device is charged (interval 310). After the CPR interval is complete  the rescuer is instructed to pause CPR 312  and shock 314 can be delivered almost immediately to the victim because the defibrillator device has already had time to charge. Because the defibrillator device is fully charged before the rescuer ceases chest compressions  the time period during which the rescuer is not delivering chest compressions to the victim can be greatly reduced and the shock can be delivered immediately or almost immediately after chest compressions are completed. For

example  the elapsed time between the end of the CPR interval and the delivery of the shock (if a shockable rhythm exists) can be less than about 5 seconds (e.g.  less than about 5 seconds  less than about 3 seconds  less than about 2 seconds  less than about 1 second  less than about 1/2 a second). In some embodiments  the length of time between the rescuer ceasing chest compressions and delivery of the shock can be simply based on the amount of time the rescuer spends locating and pressing a button on the AED device that causes the AED device to deliver the shock to the victim.

In some additional embodiments  the AED device may utilize a brief period of time (e.g.  while the rescuer locates and presses the button) after the rescuer ceases chest compressions to reconfirm the desirability of delivering the shock to the victim. For example  a rescuer can be instructed to visually inspect and confirm that a shockable rhythm exists and/or the AED device can continue to collect and analyze ECG signals (in the absence of chest compressions resulting in less artifacts in the ECG signal) to re-confirm the desirability of delivering the shock. In general  a time period for re-confirmation based on analysis of an ECG signal without chest compression artifacts can be brief (e.g.  less than about 5 seconds  less than about 3 seconds  less than about 2 seconds). The time period for re-confirmation can be based on physiological characteristics (e.g.  heart rate that is fast or slow) and/or a desired confidence level for the ECG analysis.

Because of safety issues with charging the defibrillation device to a voltage of 1000-2000 volts while the rescuer is in contact with the victim  safety interlocks can be included in a defibrillator device to ensure that the voltage is not discharged before the rescuer removes his or her hands from the victim. The defibrillator safety interlocks can include one or more software-controlled-hardware and/or software mechanisms that prevent the defibrillator from accidentally discharging outside of the unit. In order for the defibrillator to deliver a shock  the AED device confirms that a variety of software and hardware states are met during the charging process. Once the defibrillator reaches a full level of charge  a therapy button is enabled. Enabling the therapy button removes a final hardware safety interlock and selects the output for the therapy charge to the patient connector instead of the internal resistor network used to dissipate charge when a shock is not delivered. Once enabled  a rescuer presses the therapy button and the AED registers the press which closes a therapy delivery relay and delivers the defibrillation pulse. The safety interlocks control the enablement of the therapy button and a do not allow the rescuer to deliver a shock to the victim until other actions occur that disable the safety interlocks.

In some additional methods  an electrically insulating protection layer extends over the surface of the patient so that manual compressions may continue safely and unabated during the charging of the defibrillation device and delivery of the defibrillation shock. An exemplary electrically insulating protection layer is described  for example  in U.S. Patent 6 360  125  which is incorporated by reference herein in its entirety.

In some embodiments  the period for administration of chest compressions is not preset  rather the period can be variable based on the observed EGC signals. ECG analysis may start while CPR chest compressions are being administered. When the AED device determines that a shockable rhythm exists based on the ECG signals or otherwise makes a determination that the appropriate therapy would be to deliver the defibrillation shock  the AED device can begin charging. CPR chest compressions continue while the device is charging. The AED device can optionally instruct the rescuer of an amount of time that he/she should continue to administer chest compressions based on the length of time used to charge the defibrillator device. Once the device is fully charged  the rescuer can be instructed to pause chest compressions and the shock can be delivered almost immediately to the victim.

FIG. 4A is a flow chart showing actions taken to charge a defibrillation device during chest compressions associated with a CPR interval. As noted above  charging the defibrillation device in addition to analyzing an ECG signal during chest compressions can provide the advantage of reducing the amount of time that a rescuer is not administering chest compressions to the victim. In general  an interval (e.g.  a set length of time) is set for the administration of chest compressions. During this interval  the system analyzes an ECG signal and charges the defibrillation device. Safety interlocks are enabled that prevent accidental dissipation of the charge in the defibrillation device during the CPR chest compression interval. At the end of the CPR interval  a decision of whether to shock the victim is made based on the ECG signal analysis  and the stored charge is either administered to the victim or dissipated internally.

The example process here begins at box 402  where the AED analyzes an ECG signal to determine if a shockable rhythm is present in the victim. The ECG signal is measured while chest compressions are being administered to the victim. As such  the AED separates the chest compression artifact from the ECG signal components to process the ECG signal without halting the processing during CPR chest compressions (e.g.  as described in U.S. Patent 7 565  194).

At box 404  the AED determines if the current time is near the end of the CPR interval (e.g.  within about 10-30 seconds of the end of the CPR interval). Exemplary CPR intervals can be between 2 and 5 minutes (e.g.  2 minutes  3 minutes  4 minutes  and 5 minutes). If the current time within a determined window for performing chest compressions is not near the end of the CPR interval  the AED device continues to analyze the ECG signals (box 402). If the current time is near the end of the CPR interval  the AED enables safety interlocks at box 406 (though the interlocks may be enabled even before this time).

As the chest compressions continue  the AED begins charging the defibrillation device at box 408 with the safety interlocks enabled. The amount of time needed to charge the defibrillation device can vary based on the current used to charge the device and the total amount of charge desired. As such  the system begins charging the defibrillation device in advance of the end of the CPR interval such that the

defibrillation device will be fully charged at the end of the CPR interval. For example  a window for performing CPR can be determined when the CPR cycle begins  a time for charging the defibrillation device can be looked up or otherwise determined  and the system may be programmed to check  at a time in advance of the end of the window that substantially corresponds to the charging time  for whether a shockable rhythm is present

At box 410  the AED performs a final analysis of the ECG signal to determine if a shockable rhythm is present in the victim. Exemplary methods for analyzing the ECG signal to determine if a shockable rhythm exists are described  for example  in U.S. Patent 7 565  194  titled "ECG Rhythm Advisory Method " the contents of which are hereby incorporated by reference in their entirety. If a shockable rhythm is not observed  at box 422  the AED instructs the rescuer to continue chest compressions. Thus  if a shockable rhythm does not exist  the victim receives uninterrupted chest compressions. Such chest compressions may not place the heart back into normal operation  but they may nonetheless maximize perfusion of blood through the heart until a more highly -trained rescuer can arrive and take over.

At box 424  the AED dissipates the charge from the defibrillation device without delivering a shock to the victim. For example  the AED can dissipate the stored charge using a resistor network inside the AED device such that the charge can be dissipated without requiring the rescuer to discontinue chest compressions. The dissipation may occur by dumping the charge  for example. The charge may also be "recycled" back into a battery on the device so as to extend the battery life.

If a shockable rhythm is observed  at box 414  the AED device instructs the rescuer to discontinue chest compressions. For example  the AED device can provide audible instructions to the rescuer via a speaker and/or can provide a visual instruction to the rescuer via a display device. At box 416  the AED disables the safety interlocks  thus making it possible for the shock to be delivered through electrodes that are attached to the victim.

At box 418  the AED device delivers the defibrillation shock to the victim. Such delivery may occur in response to the rescuer pressing a button on the AED to provide a command to delivered the shock. The shock may also be delivered automatically  such as after the AED voices a command to stand clear of the victim. The shock is delivered without significant delay after the cessation of chest compressions because the device has been previously pre-charged while the chest compressions were being administered.

At box 420  the AED device instructs the user to resume chest compressions. This initiates another CPR cycle during which a similar ECG analysis will be performed. The process just described may thus be repeated until a shock succeeds in placing the victim""s heart roughly back into a normal operating mode  or until additional caregivers arrive to attempt different resuscitation approaches.

In some embodiments  a reconfirmation of the desirability to deliver the defibrillation shock to the victim is performed after the rescuer ceases chest compressions. Because the re-confirmation is performed when the rescuer is not delivering chest compressions  the ECG signals analyzed by the AED device during the reconfirmation are expected to be less noisy and have less artifacts because artifacts from the chest compressions are no longer present. As such  an ECG analysis may have higher degree of confidence. In general  as described above  a time period for reconfirmation based on analysis of an ECG signal without chest compression artifacts can be brief (e.g.  less than about 5 seconds  less than about 3 seconds  less than about 2 seconds).

In some embodiments  the AED device can determine whether to perform a reconfirmation analysis based on one or more factors associated with the prior EGC analysis such as a certainty value. For example  if the prior EGC analysis results in a high certainty that delivering the defibrillation shock to the victim is the appropriate therapy (e.g.  a high certainty of conversion to a perfusing rhythm) then the AED may deliver the shock nearly immediately after the rescuer ceases chest compressions (e.g. without a reconfirmation period). On the other hand  if the prior EGC analysis has a lower certainty that delivering the defibrillation shock to the victim is the appropriate therapy then the AED may perform a reconfirmation analysis before making a final determination of whether to deliver the defibrillation shock. Additionally or alternatively a determination of whether to perform a reconfirmation analysis can be based on a confidence value associated with the level of confidence that the EGC signal analysis is correct. For example  if the signal is extremely noisy and has a large presence of artifacts  the confidence of the analysis may be lower making it desirable to reconfirm the analysis in the absence of the chest compressions.

FIG. 4B is a flow chart showing actions taken to charge a defibrillation device using different current levels that are selected based on the likelihood of a shockable rhythm being observed. Portable AED devices may be powered by a battery or other power supply having a limited lifetime. In order to conserve power for future uses of the AED device or for the administration of multiple shocks to a single victim  various charging algorithms can be used. In some examples  an AED device makes a determination of whether a shockable rhythm exists in the victim and only charges the defibrillator device if a shockable rhythm exists. Such a charging algorithm conserves power because if a shockable rhythm is not observed  the AED device does not charge the defibrillator and then dump or dissipate the charge.

The example process begins at box 425  where the AED analyzes an ECG signal while chest compressions are being administered to a victim to determine if a

shockable rhythm is likely to be present in the victim at the end of the CPR interval (e.g.  as described in U.S. Patent 7 565  194). At box 426  the AED determines if a shockable rhythm is likely to be present in the victim at the end of the CPR interval. While the CPR interval will continue regardless of the outcome of the analysis  the determination is used to decide whether to begin charging the defibrillator device. The time at which to make such a determination may be set by a determination of how long it will take to charge the defibrillator device. When different possible rates of charge are available to the system  and maximum time charge can be set for the ECG analysis  a rate of charge may be determined  and then the actual charging may begin at a time preceding the end of CPR that is substantially the amount of time the charge will take at the computed rate of charge.

A threshold for determining whether to pre-charge the defibrillator can be different from a threshold used to determine whether to administer a shock to the victim. For example  because the determination is used to decide whether to pre-charge the AED device  a lower threshold may be used such that the device will be fully charged at the end of the CPR interval if a shock may be administered. For example  an accuracy measure can be used to set the thresholds. For example  an observed signal resulting in a high accuracy value (e.g.  a confidence of greater than about 90%) can be used as to set a threshold for determining whether to administer a defibrillation shock to the victim while a lower confidence (e.g.  a confidence of 50% or greater) can be used to set a threshold for determining whether to begin charging the defibrillation device. For example  an AMSA number that is associated with a certain accuracy level in predicting a successful conversion can be used to set the thresholds for deciding whether to pre-charge the defibrillator  the rate of charging the defibrillator  and whether to administer the defibrillation shock. This AMSA number can be customized based on a request of the rescuer or the medical director. For example  an AMSA number that is associated with a accuracy level of 90% or greater (e.g.  90% or 95%) in predicting a successful conversion can be used to set the threshold for administering a defibrillation shock and an AMSA number that is associated with a accuracy level of 70% or greater (e.g.  70%  80%  90%) in predicting a successful conversion can be used to set the threshold for deciding whether to pre-charge the defibrillator. In other examples  an AMSA number that is associated with an accuracy level of 70% or greater (e.g.  70%  80%  90%) in predicting a successful conversion can be associated with the fastest possible rate in charging the defibrillator; The lower value the AMSA number is  the rate of charging is set to (e.g.  half speed in charging when an AMSA number associated with an accuracy level of 50% is observed). In some embodiments  other predictors of conversion success (e.g.  SCE) can be used.

If a shockable rhythm is not likely to be present in the victim at the end of the CPR interval  the AED continues to receive and analyze the ECG signals. At box 428 near the end of the CPR cycle  the AED device performs a final analysis of the ECG signal to determine whether a shockable rhythm exists. This second determination of whether a shockable rhythm exists serves as a confirmation that a shockable rhythm still does not exist  so that a rescuer does not forego providing a shock to the victim in a situation where the patient""s condition has changed in a manner that would make a shock would be beneficial.

In contrast  if the system determines that a shockable rhythm is likely to exist  at box 427  the AED pre-charges the defibrillation device. This charging occurs while the rescuer is administering the CPR chest compressions. At box 428 near the end of the CPR cycle  the AED device performs a final analysis of the ECG signal.

At box 429  the AED device determines whether a shockable rhythm exists. This second determination of whether a shockable rhythm exists serves as a confirmation that a shockable rhythm still exists  so that a rescuer is not led to give a shock to a patient when the patient""s condition has changed in a manner that would make the shock essentially futile. A different threshold can be used for the

determination of whether to administer the shock to the victim than was used to determine whether to pre-charge the defibrillator.

If a shockable rhythm does not exist at this later time and under this later standard (though the standard may also be the same for deciding whether to pre-charge and deciding whether to remove the safety interlocks and allow the shock actually to be delivered)  the AED instructs the rescuer to continue chest compressions at box 434 such that the victim receives uninterrupted chest compressions. At box 435  the AED dissipates the charge (e.g.  using one or more of the methods described herein) from the defibrillation device without delivering a shock to the victim if the device was pre-charged (e.g.  at box 427).

If a shockable rhythm is observed  at box 430  the AED device determines whether the defibrillator was pre-charged (e.g.  at box 427) and charges the defibrillator if it was not previously pre-charged (or completes any still-incomplete charging). At box 431  the AED device instructs the rescuer to discontinue chest compressions (e.g.  using one or more of the methods described herein). At box 432  the AED device delivers the shock and at box 432  the AED device instructs the user to resume chest compressions. This initiates another CPR cycle during which a similar ECG analysis will be performed.

FIG. 4C is a flow chart showing actions taken to charge a defibrillation device using different current levels based on the likelihood of a shockable rhythm being observed. One exemplary way to conserve power in an AED is to charge the AED device at a lower current over a longer period of time (e.g.  over a period of at least 30 seconds)  resulting in less of a drain on the batter power as compared to charging the AED device to the same total charge using a higher current and a shorter period of time (e.g.  over a period of at most 10 seconds). A percentage calculated by dividing the lower charging current by the higher charging current can be greater than about 50% (e.g.  greater than about 50%  greater than about 60%  greater than about 75%) and less than about 90% (e.g.  less than about 90%  less than about 80%).

Charging the AED device over a longer period of time at a lower current can occur during the CPR interval because the typical CPR interval is between 2-5 minutes. Both charging the device at a lower current (that is selected to permit full or substantially full charging during the available charging interval before a shock may be needed) and/or only charging the device if it is likely that a shock will be administered to the victim can contribute to an extended battery life for the AED device. Drawing less total current from the battery can provide additional advantages such as enabling the use of a smaller battery (and thereby enabling a smaller and lighter AED) and/or enabling the use of alternative power devices such as solar power and/or human generated power.

In one embodiment  a "crank" generator may be employed. Since the time available to charge the defibrillator capacitor can be increased to as much as 3 - 10 minutes using the systems and methods described herein  a 200 joule capacitor only requires at most approximately a 1.5 watt power source  assuming a 3 minute charge

duration and a high voltage flyback circuitry efficiency of 75%. Due to leakage of a typical film capacitor at maximum voltage of approximately 2 Watts  a generator of 2.5 - 3 Watts would be required. Such a power supply may be an external hand crank power supply available commercially (SuperBattery with Crank Generator  Teledex  Inc.  N.J.)  or a built-in crank generator in the defibrillator with a power output sufficient to charge the defibrillator capacitor in the allotted time. As part of the generator  an additional energy storage element will preferably be included  for instance a battery as contained in the Superbattery described above  or a so-called "ultracapacitor"  such as that manufactured by Maxwell Technologies (San Diego)  for instance the 350 Farad  part number BCAP0350 E270 Ti l . The ultracapacitor is used to maintain power for the low- voltage circuitry such as signal amplifiers and digital processing circuitry when the rescuer has stopped providing mechanical energy to the generator. The mechanical energy for the generator may alternatively be contained in a structure positioned on the patient""s sternum  which will be compressed during cardiopulmonary resuscitation. Currently  devices exist commercially (CPR-STATPADZ  ZOLL Medical  Chelmsford  MA) which measure the performance of the rescuer doing chest compressions by measuring the compression depth via an accelerometer sensor within a low-profile housing positioned under the rescuers hands while they are compressing the patient""s sternum during CPR. The housing may additionally be constructed to flexibly deform during sternal compressions  thus causing motion of the actuator of a generator  for instance a linear motion electric power generator as described in U.S. Patent 5 818  132. A typical patient requires approximately 100 pounds of force to depress the sternum to the required depth of 2 inches  as per the American Heart Association recommendations. Thus  by allowing for a deformation of the housing of 0.5 - 1 inches would increase the compression depth of the rescuer to 2.5 - 3 inches to achieve the same sternal depth of 2 inches  but would provide the requisite 2.5 - 3 Watts of necessary power  assuming a generator efficiency of 40%. Alternatively  the housing may be a spring-loaded two piece housing with accelerometer and generator contained within the housing  the upper portion of the generator actuator affixed to the upper portion of the housing  the generator and the lower portion of the actuator affixed to the lower housing  and power generated when the spacing between the upper and lower housings is changed.

In another embodiment  the lid of the AED might be surfaced with a solar cell  thus providing approximately 100 square inches of available surface area. Standard  commercially available amorphous Silicon crystal cells currently provide

approximately 45 milliwatts per inch squared. This power can be doubled by employing a more expensive crystalline cell as well as alternative structures. Thus  the solar cell would be able to provide 4 - 10 Watts of power  which is more than sufficient for the systems and methods described herein. As with the human powered generator approach  an electrical energy storage element would be included  such as an ultracapacitor  in addition to the defibrillator capacitor  for powering the analog and digital low-voltage electronics  if for instance a shadow from the rescuer passes in front of the solar cells during device use. Thus  even with batteries that have failed or whose performance has degraded to the point that they are unable to power the defibrillator  it is now possible to have a backup power source for use in emergencies  not currently available with existing technology. In the preferred embodiment  a fail-safe switch  relay or transistor would be employed that would disconnect the failed batteries from the electronics  so that power would not be diverted from the generator or solar cell by the batteries during operation.

Because the defibrillator capacitor can be charged over a significantly increased period of time  the peak charging current is significantly decreased by a factor of ten or more. This allows for significantly smaller batteries to be used to power the defibrillator. This allows for significantly smaller batteries to be used to power the defibrillator. In general  the batteries can include one or more primary cells and/or one or more secondary (e.g.  rechargeable) cells. Examples of significantly smaller batteries that can be used to power the defibrillator include any battery (or combination of multiple batteries) with a relatively low power output of  for example  less than about 10W (e.g.  less than about 10W  less than about 7 W  less than about 5W  less than about 4W  less than about 3W). In some examples  the power output can be greater than about 2.5W and less than 10W (e.g.  between about 2.5W and about 10W  between about 2.5W and about 7W  between about 2.5W and about 5W  between about 2.5W and about 4W  between about 2.5W and about 3W). In one particular example  the current ZOLL AEDPlus requires ten lithium CRT 23 commercial batteries to power the defibrillator  at a significant size  weight and cost expense. With the systems and methods described herein  this can be reduced to 1  or at most  2 CR123 batteries. In addition  it is now possible to use even smaller alkaline batteries  such as a standard commercially-available ""C size alkaline cell.

At box 436  while chest compressions are being administered  the AED analyzes an ECG signal (e.g.  as described in U.S. Patent 7 565  194) and at box 437  the AED determines if a shockable rhythm is likely to be present in the victim at the end of the CPR interval. While the CPR interval will continue regardless of the outcome of the analysis  the determination is used to decide whether to begin charging the defibrillator device.

If a shockable rhythm is not likely to be present in the victim at the end of the CPR interval  the AED continues to receive and analyze the ECG signals. At box 439  near the end of the CPR cycle  the AED performs a final analysis of the ECG signal to determine whether a shockable rhythm exists. The analysis may also continue until a shockable rhythm is present.

In contrast  if the system determines that a shockable rhythm is likely to exist (either initially or upon further monitoring and analysis)  at box 438  the AED device begins pre-charging the defibrillation device at a low charging current. In other examples  the charging current can be based on the length of time remaining in the CPR interval. For example  a charging current can be selected such that the device will be fully charged at the end of the CPR interval. This may result in the charging occurring at a low rate over an extended period of time (e.g.  over a period of time greater than about 30 seconds  over a period of time greater than about 45 seconds  over a period of time greater than about 1 minute). For example  if a shockable rhythm is determined initially  the charging rate may be relatively low  whereas if there was no initial shockable rhythm but the device senses a shockable rhythm later in the chest compression cycle  the charging rate may be relatively fast. This charging occurs while the rescuer is administering the CPR chest compressions (though some may occur after the end of the provision of CPR chest compressions  though not enough that it would create an substantial effect on the timing of the CPR).

At box 439 near the end of the CPR cycle  the AED device performs a final analysis of the ECG signal  and at box 440  the AED device determines whether a shockable rhythm exists. If a shockable rhythm does not exist  the AED instructs the rescuer to continue chest compressions at box 450 such that the victim receives uninterrupted chest compressions. At box 452  the AED dissipates the charge (e.g.  using one or more of the methods described herein) from the defibrillation device without delivering a shock to the victim if the device was pre-charged (e.g.  at box 438).

If a shockable rhythm is observed  at box 441  the AED device determines whether the defibrillator has reached a full level of charge and charges the defibrillator to the full level of charge (if needed) at a high current. For example  while the pre-charging can occur at a low current over an extended period of time  charging to reach the full charge if the device is not fully charged in time (or charging if not pre-charged) can occur at a high current and during as short of period as is practical.

At box 444  the AED device instructs the rescuer to discontinue chest compressions (e.g.  using one or more of the methods described herein). At box 446  the AED device delivers the shock and at box 448  the AED device instructs the user to resume chest compressions. This initiates another CPR cycle during which a similar ECG analysis will be performed.

FIG. 4D is a flow chart showing actions taken to adaptively charge a defibrillation device to a level (e.g.  a desired total voltage or charge) selected based on ECG analysis. For example  a level of charge for the defibrillation device (and a total amount of charge delivered to the victim) can be adaptively determined based on factors related to the ECG analysis such as the amplitude  frequency of the ECG signal  and/or an AMSA value. For example  if a victim is experiencing VF with a high amplitude ECG signal  only a low level of energy in the shock may be used. In contrast  in situations where it is not likely that conversion to a perfusing rhythm will occur with only a low energy shock such as situations in which the ECG signal exhibits a low amplitude  then the defibrillation device can be charged to a higher energy level.

In some implementations  an amplitude magnitude spectrum area (AMSA) value can be used to determine how to charge the defibrillation device and when to administer a defibrillation shock. For example  a high AMSA value is believed to be correlated to a high likelihood of conversion to a perfusing rhythm. The AMSA value can be monitored and the level of shock and/or length of time chest compressions are

administered can be modified based on a threshold AMSA value and/or trends observed in the AMSA value. For example  a shock could be administered when a change (e.g.  a decrease) in the AMSA value is observed by systems provided in an AED device. The AMSA value can also be used to determine the rate in charging the defibrillator. For example  an AMSA number that is associated with an accuracy level of 70% or greater (e.g.  70%  80%  90%) in predicting a successful conversion can be associated with the fastest possible rate in charging the defibrillator; The lower value the AMSA number is  the rate of charging is set to (e.g.  half speed in charging when an AMSA number associated with an accuracy level of 50% is observed).

In FIG. 4D at block 462  while chest compressions are being administered  the AED device analyzes an ECG signal  and at box 464  the AED device determines if a shockable rhythm is likely to be present in the victim at the end of the CPR interval. If a shockable rhythm is not likely to be present in the victim at the end of the CPR interval  the AED instructs the rescuer to continue chest compressions for another CPR interval at box 468 and continues to receive and analyze the ECG signals. If the system determines that a shockable rhythm is likely to exist  at box 466  the AED device determines a level of charge based on an analysis of the ECG signal. For example  the level of charge or the rate of charging can be based on an amplitude of the ECG signal  a frequency of the ECG signal  and/or and AMSA value of the ECG signal. The level of charge can vary from a low charge to a high charge. In general  if the AMSA value is used  the level of charge is proportional to the AMSA value such that the device is charged to a higher level if the AMSA value is higher. At box 470  the AED charges the defibrillation device to the determined level of charge. The rate of charging can also vary from a slow charging rate to a fast charging rate: for example  if the AMSA value is used  the charging rate can be proportional to the AMSA value such that the device is charged faster if the AMSA value is higher.

At box 472  near the end of the CPR interval  the AED device performs a final analysis and determines (box 474) if a shockable rhythm is present. If a shockable rhythm does not exist  the AED instructs the rescuer to continue chest compressions at box 482 such that the victim receives uninterrupted chest compressions. At box 483  the AED dissipates the charge (e.g.  using one or more of the methods described herein) from the defibrillation device without delivering a shock to the victim.

If a shockable rhythm is observed  at box 476  the AED instructs the rescuer to discontinue chest compressions (e.g.  using one or more of the methods described herein). At box 478  the AED device delivers the shock and at box 480  the AED device instructs the user to resume chest compressions.

Other data besides ECG data may be included as part of the determination of whether a shockable rhythm exists and may be incorporated into the analysis algorithm  for instance pulse oximetry  capnography  respiration  impedance cardiography  and blood pressure measurements. At least some of the data may remain in the time domain without any Fourier or other transform method being performed on it. Pulse oximetry  impedance cardiography  and blood pressure measurements may be used to augment the ECG to determine if a pulse is present. Capnography may be used to determine the overall effectiveness of cardiopulmonary resuscitation. The additional measures can also include measurement of velocity or acceleration of chest compression during chest compressions according to the techniques taught by U.S. Patent 7 220 335  Method and Apparatus for Enhancement of Chest Compressions During Chest Compressions  the contents of which are hereby incorporated by reference in their entirety and U.S. Patent Application 11/430 579 titled ECG rhythm advisory method the contents of which are hereby incorporated by reference in their entirety.

In some embodiments  the cross-correlation between the ECG signal (with CPR artifact) and the CPR signal (in the form of compression acceleration  velocity  or displacement) can be calculated. Based on the strength of the cross-correlation between the ECG signal and the CPR signal  the system can select an appropriate analysis method to remove the artifacts from the ECG signal and determining if a shockable rhythm exists in the ECG signal. For example  a high cross-correlation value between the ECG signal and the CPR signal indicates that the majority of the artifact is from the chest compression and thus an analysis method designed for ECG with CPR artifact may be more reliable than other analysis methods. Alternatively  a low cross-correlation value typically indicates that there is strong non-CPR-related artifact in the recorded ECG signal.

FIGS. 5A and 5B illustrate an example of the observed ECG signal (FIG. 5A) showing strong cross-correlation with the CPR acceleration signal (FIG. 5A)  which indicates that the ECG signal is free from non-CPR noise. The strong cross correlation can be observed based on the similarity in the shape of the CPR signal and the ECG signal. The cross correlation can be computed automatically during the analysis of the ECG signal.

As noted above  a low cross-correlation value between the ECG signal and the CPR signal typically indicates that there is strong non-CPR-related artifact in the recorded ECG signal. With the presence of the non-CPR-related artifact  the ECG analysis performed during CPR may be less reliable (or may not be reliable). Due to the lesser reliability of the ECG analysis  the system can utilize a longer period of CPR-free time in a re-confirmation analysis (e.g.  a longer analysis period can be utilized after the cessation of CPR and prior to the determination of whether a shockable rhythm exists). FIGS. 6A and 6B illustrate an example of the observed ECG signal (FIG. 6A) with weak cross-correlation with the CPR acceleration signal (FIG. 6B). This indicates that the ECG has strong non-CPR noise and a longer of re-confirmation analysis period can be used.

The information processing technique can include but is not limited to simple combining rules or math  neural networks  expert systems incorporating fuzzy or standard logic  or other artificial intelligence techniques. For example  multiple factors can be combined to make a determination of whether to defibrillate. In some situations  even if a shockable rhythm exists (e.g.  as determined based on the ECG analysis) the AED device may not recommend delivering the shock to the patient because one or more other factors suggest that another treatment would likely be more effective. For example  if a shockable rhythm exists but the quality of CPR chest compressions as measured based on one or more of the velocity  acceleration  or depth of the compressions is low  then the AED device could recommend continuing chest compressions to increase blood circulation rather than stopping the chest compressions to deliver the shock.

In some embodiments  the AED device can combine different measures and output results related to the desirability of defibrillation and/or the effectiveness of the chest compressions being delivered by the rescuer. Exemplary outputs can include statements such as "strong need for defibrillation " "weak need for defibrillation " "faster chest compressions needed " or "additional chest compressions needed."

In some embodiments  the AED device can deliver the defibrillation shock during the chest compression cycle (e.g.  while the rescuer is delivering the chest compressions). For example  the AED can synchronize of the defibrillation shock to the chest compression cycle. Delivery of the defibrillation shock during the early portion (approximately the first 300 milliseconds) of the decompression (diastolic) phase of the chest compression cycle can improve the likelihood of success of the delivered shock. The decompression phase begins when the rescuer reduces compression force on the chest  allowing the chest to rise  and the heart to expand. The AED device can detect chest compression phase and timing information indicative of the start of the decompression phase and initiate delivery of the electromagnetic therapy within 300 milliseconds of the start of the decompression phase. In some

embodiments  delivery of electromagnetic therapy can be initiated within 25 - 250 milliseconds of the start of the decompression phase. Circuitry and processing for the detection of chest compression phase timing information can include a pressure sensor and/or an accelerometer. Exemplary methods for synchronizing defibrillation with chest compression phase are described in U.S. Patent Application 12/263 813 titled Synchronization of Defibrillation and Chest Compressions  the contents of which are hereby incorporated by reference in their entirety.

Large self-adhesive electrode pads (~5" in diameter) are typically used to deliver defibrillation therapy to patients. The pads also provide ECG monitoring through the conductive surfaces that deliver therapy. In one implementation  additional small (-0.5" diameter) ECG electrodes can be integrated into the large pads.

In one embodiment  the two small ECG electrodes and large pads are configured such that there at least two mutually orthogonal ECG leads are generated. The vector sum of these leads generates a trajectory over time. The same methods for trajectory analysis described above may be used to analyze this trajectory as well.

FIG. 7 shows a defibrillation device 500 with a display portion 502 that provides information about patient status and CPR administration quality during the use of the defibrillator device. The data is collected and displayed in an efficient and effective manner to a rescuer. As shown on display 502  during the administration of chest compressions  the device 500 displays information about the chest compressions in box 514 on the same display as a filtered ECG waveform 510 and a C02 waveform 512 (alternatively an Sp02 waveform can be displayed).

During chest compressions  the ECG waveform is generated by gathering ECG data point and accelerometer readings and filtering the motion induced (e.g.  CPR induced) noise from the ECG waveform. Measurement of velocity or acceleration of chest compression during chest compressions can be performed according to the techniques taught by U.S. Patent 7 220 335  Method and Apparatus for Enhancement of Chest Compressions During Chest Compressions  the contents of which are hereby incorporated by reference in their entirety. Displaying the filtered ECG waveform helps clinicians reduce interruptions in CPR because the displayed waveform is easier for the rescuer to decipher. If the ECG waveform is not filtered  artifacts from manual chest compressions make it difficult to discern the presence of an organized heart rhythm unless compressions are halted. Filtering out this artifact allows clinicians to view the underlying rhythm without stopping chest compressions.

The CPR information in box 514 is automatically displayed when compressions are detected. The information about the chest compressions displayed in box 514 includes rate 518 (e.g.  number of compressions per minute) and depth 516 (e.g.  depth of compressions in inches or millimeters). The rate and depth of compressions can be determined by analyzing accelerometer readings. Displaying the actual rate and depth data (in addition to or instead of an indication of whether the values are within or outside of an acceptable range) is believed to provide useful feedback to the rescuer. For example  if an acceptable range for chest compression depth is between 1.5-2 inches  providing the rescuer with an indication that his/her compressions are only 0.5 inches can allow the rescuer to determine how to correctly modify his/her

administration of the chest compressions.

The information about the chest compressions displayed in box 514 also includes a perfusion performance indicator (PPI) 520. The PPI 520 is a shape (e.g.  a diamond) with the amount of fill in the shape differing to provide feedback about both the rate and depth of the compressions. When CPR is being performed adequately  for example  at a rate of about 100 compressions/minute (CPM) with the depth of each compression greater than 1.5 inches  the entire indicator will be filled. As the rate and/or depth decreases below acceptable limits  the amount of fill lessens. The PPI 520 provides a visual indication of the quality of the CPR such that the rescuer can aim to keep the PPI 520 completely filled.

As shown in display 500  the filtered ECG waveform 510 is a full length waveform filling the entire span of the display device while the second waveform (e.g.  the C02 waveform 512) is a partial length waveform and fills only a portion of the display. A portion of the display beside the second waveform provides the CPR information in box 514. For example  the display splits the horizontal area for the second waveform in half  displaying waveform 512 on left and CPR information on the right in box 514.

The data displayed to the rescuer can change based on the actions of the rescuer. For example  the data displayed can differ based on whether the rescuer is currently administering CPR chest compressions to the patient. Additionally  the ECG data displayed to the user can change based on the detection of CPR chest compressions. For example  the adaptive filter can automatically turn ON or OFF based on detection of whether CPR is currently being performed. When the filter is on (during chest compressions)  the filtered ECG data is displayed and when the filter is off (during periods when chest compressions are not being administered ) unfiltered ECG data is displayed. An indication of whether the filtered or unfiltered ECG data is displayed can be included with the waveform.

FIG. 8A is a flow chart showing actions taken to modify information presented on a display of a defibrillation device based on the detection of CPR chest

compressions. The exemplary process begins at box 602 with collection of various data during the administration of chest compressions. The measurements can include measurement of EGC signals  C02  Sp02  and/or CPR chest compression quality measurements such as depth  rate  and release information. At box 604  the

defibrillator device displays CPR information  a filtered ECG waveform  and a second waveform such as C02  Sp02  or chest compressions on the display device. As described above  displaying this combination of information on a single display device during CPR administration provides an easy to view summary of the patient status and CPR quality.

At box 606  the defibrillation device determines whether CPR chest

compressions are still being administered. For example  data collected from an

accelerometer can be used to determine whether the rescuer is still administering chest compressions. If the user is still administering chest compressions  the system continues to display both the CPR information  the filtered ECG waveform  and the second waveform. If the defibrillation device detects that the rescuer has ceased administration of chest compressions  at box 608  the defibrillation device modifies the information to present on the display and at box 609 displays the modified information. An exemplary modification of the information presented on the display can include automatically switching from a filtered ECG waveform to an unfiltered ECG waveform upon the detection of the cessation of chest compressions.

At box 610  the defibrillation device determines whether chest compressions have been resumed. If chest compressions have not been resumed  the defibrillation device continues to display the information from the modified display 609. If chest compressions have been resumed  the defibrillation device modifies the display to revert back to showing the CPR information  filtered ECG waveform  and the C02 or Sp02 waveform.

FIG. 8B shows exemplary information displayed during the administration of CPR chest compressions while FIGS. 6C and 6D show exemplary information displayed in the absence of CPR chest compressions. The defibrillation device automatically switches the information presented based on whether chest compressions are detected.

An exemplary modification of the information presented on the display can include automatically switching one or more waveforms displayed. In one example  the type of measurement displayed can be modified based on the presence or absence of chest compressions. For example  C02 or depth of chest compressions may be displayed (e.g.  a C02 waveform 620 is displayed in FIG. 8B) during CPR

administration and upon detection of the cessation of chest compressions the waveform can be switched to display an Sp02 or pulse waveform (e.g.  an Sp02 waveform 622 is displayed in FIG. 8C).

Another exemplary modification of the information presented on the display can include automatically adding/removing the CPR information from the display upon detection of the presence or absence of chest compressions. As shown in FIG. 8B  when chest compressions are detected  a portion 624 of the display includes

information about the CPR such as depth 626  rate 628 and PPI 630. As shown in FIG. 8C  when CPR is halted and the system detects the absence of CPR chest compressions  the defibrillation device changes the CPR information in the portion 624 of the display to include an indication 632 that the rescuer should resume CPR and an indication 634 of the idle time since chest compressions were last detected. In other examples  as shown in FIG. 8D  when CPR is halted  the defibrillation device can remove the portion of the display 624 previously showing CPR data and can display a full view of the second waveform. Additionally  information about the idle time 636 can be presented on another portion of the display.

In some examples  the defibrillator device automatically switches between a filtered and an unfiltered ECG waveform based on the presence or absence of chest compressions. For example  an ECG waveform without filtering can be displayed when chest compressions are not detected while a filtered ECG waveform can be displayed when chest compressions are detected. For example  FIG. 8E shows an ECG waveform 640 at the time chest compressions are first initiated. A first portion 644 of the ECG waveform displays an unfiltered ECG signal. When the defibrillator device determines that chest compressions are being performed  the device filters the ECG signal and displays a filtered ECG signal as shown in portion 642. FIG. 9A is a flow chart showing actions taken to provide an indication of CPR quality on a display of a defibrillator device. At box 700  during CPR chest compressions the defibrillator device analyzes an ECG signal and at box 702 the defibrillator device collects information about chest compressions by measuring depth and rate of compressions. The depth and rate of compressions can be determined based on measurements collected by an accelerometer. At box 704  the defibrillator device displays a filtered ECG signal  information about the depth of CPR chest compressions  and information about the rate of CPR chest compressions on a single user interface. At box 706  the defibrillator device determines whether the depth and rate of CPR chest compressions are within acceptable ranges by comparing the depth and rate measurements to threshold values that indicate acceptable values for the depth and rate. If the defibrillator device determines that the depth and rate are within an acceptable range  the defibrillator device continues to monitor the quality of chest compressions. On the other hand  if the defibrillator device determines that the depth and rate are outside of the acceptable range  the defibrillator device modifies the display to provide a visual indication that the depth and rate are outside of the acceptable range. The visual indication can be provided in various ways such as a graphical representation  a highlighting of particular values that are outside of the acceptable ranges  and/or a change in the color in which certain information is displayed. For example  if the depth or rate is within the acceptable range the value could be displayed in green font  if the depth or rate is near the boundaries of the acceptable range the value could be displayed in yellow font  and if the depth or rate is outside of the acceptable range the value could be displayed in red font. Other colors or indicators can be used.

FIG. 9B shows exemplary data displayed during the administration of CPR chest compressions when the CPR quality is within acceptable ranges while FIG. 9C shows modifications to the display when the CPR quality is outside of the acceptable range.

In the example shown in FIG. 9C  the rate of chest compressions has dropped from 154 compressions per minute (FIG. 9B) to 88 compressions per minute. The defibrillator device determines that the compression rate of 88 compressions per minute is below the acceptable range of 100-200 compressions per minute. In order to alert the user that the compression rate has fallen below the acceptable range  the defibrillator device provides a visual indication 718 to emphasize the rate information. In this example  the visual indication 718 is a highlighting of the rate information. Similar visual indications can be provided based on depth measurements when the depth of the compressions is more shallow or deeper than an acceptable range of depths.

In the examples shown in FIGS. 9B and 9C  a perfusion performance indicator (PPI) 716 provides additional information about the quality of chest compressions during CPR. The PPI 716 includes a shape (e.g.  a diamond) with the amount of fill in the shape differing based on the measured rate and depth of the compressions. In FIG. 9B  the depth and rate fall within the acceptable ranges (e.g.  at least 100

compressions/minute (CPM) and the depth of each compression is greater than 1.5 inches) so the PPI indicator 716a shows a fully filled shape. In contrast  in FIG. 9C when the rate has fallen below the acceptable range  the amount of fill in the indicator 716b is lessened such that only a portion of the indicator is filled. The partially filled PPI 716b provides a visual indication of the quality of the CPR is below an acceptable range.

In addition to measuring information about the rate and depth of CPR chest compressions  in some examples the defibrillator device provides information about whether the rescuer is fully releasing his/her hands at the end of a chest compression. For example  as a rescuer tires  the rescuer may begin leaning on the victim between chest compressions such that the chest cavity is not able to fully expand at the end of a compression. If the rescuer does not fully release between chest compressions the quality of the CPR can diminish. As such  providing a visual or audio indication to the user when the user does not fully release can be beneficial.

FIG. 1 OA is a flow chart showing actions taken to provide an indication of whether a rescuer is fully releasing between chest compressions. At box 802  the defibrillator device measures depth  rate  and release of CPR chest compressions. The depth  rate  and release of CPR chest compressions can be determined based on information collected from an accelerometer. Based on the collected information  at box 804  the defibrillator determines whether the rescuer is fully releasing between chest compressions. At box 806  the defibrillator provides an indicator on a display that includes information about whether the rescuer is fully releasing. For example  the display on the defibrillator can include a release indication box where the amount of fill in the box varies to indicate whether the rescuer is fully releasing between chest compressions. For example  as shown in FIG. 10B  when the rescuer is fully releasing the box 820 can be fully filled. When the rescuer is not fully releasing the amount of fill in the release indication box is decreased such that the box is only partially filled (e.g.  as shown in box 822 of FIG. IOC).

As shown in FIG. 1 1  in some examples  a visual representation of CPR quality in a CPR Compression bar graph 900. The CPR Compression Bar Graph 900 can be automatically displayed upon detection of CPR chest compressions.

In the CPR compression bar graph 900  the extent or height of a particular bar conveys information about a depth of compression. For example  bar 902 has a greater extent than bar 904 indicating that the depth of the compression associated with bar 902 was greater than the depth of the compression associated with bar 904. Ranges of preferred depths can be indicated by horizontally extending lines on the CPR

compression bar graph 900. The lines can provide an indication of acceptable depths (e.g.  region 910) and depths that are too shallow (e.g.  region 912). Additionally  compressions falling outside of the acceptable range can be highlighted in a different color than compressions falling within the acceptable range of compression depth.

In the CPR compression bar graph 900  the y-axis represents time and each compression is displayed to allow the rescuer to view the rate of compressions. For example  region 906 includes closely spaced bars in comparison to region 908 indicating that the rate of chest compressions was greater in the time period associated with region 906 than in the time period associated with region 908.

While at least some of the embodiments described above describe techniques and displays used during manual human-delivered chest compressions  similar techniques and displays can be used with automated chest compression devices such as the AutoPulse device manufactured by ZOLL Medical  MA.

While at least some of the embodiments described above describe techniques and displays used in conjunction with an AED device  similar techniques and displays can be used with other defibrillator devices. Exemplary professional grade defibrillator devices include the A series  E series or M series devices manufactured by ZOLL Medical  MA and the Philips MRX or Philips XL devices.

Additionally  the defibrillator may take the form of a wearable defibrillator such as the LifeVest  manufactured by ZOLL Medical (Chelmsford  MA).

Many other implementations other than those described may be employed  and may be encompassed by the following claims.

WE CLAIM:-

1. A method for monitoring patient activity using an external defibrillator  the method comprising:

obtaining data regarding chest compressions performed on the patient;

determining values for depth and rate of a plurality of the chest compressions; displaying on a graphical display screen of the defibrillator  indications of the determined values for depth and rate.

2. The method of claim 1  wherein determining the values for depth and rate comprises determining numeric values in terms of distance for depth and compressions per minute for rate  and wherein displaying the indications of the determined values for depth and rate comprises displaying numbers that correspond to the determined numeric values.

3. The method of claim 1  further comprising displaying an icon adjacent the indications of the determined values that indicates whether the chest compressions are being performed properly.

4. The method of claim 3  wherein a color of the icon changes based on whether the chest compressions are being performed properly or improperly.

5. The method of claim 1  further comprising receiving information about the patient""s heart activity and displaying on the graphical display  with the determined values for depth and rate  an electrocardiogram of the patient.

6. The method of claim 5  wherein displaying the electrocardiogram comprises moving an electrocardiogram trace laterally across the display

7. The method of claim 6  further comprising displaying an unfiltered electrocardiogram  sensing that chest compressions have commenced on the patient  and subsequently displaying a filtered electrocardiogram.

8. The method of claim 7  further comprising momentarily displaying on a trace of the electrocardiogram  an unfiltered portion showing compression artifacts  between another unfiltered portion and a filtered portion.

9. The method of claim 1  further comprising displaying second data from the patient in coordination with the electrocardiogram.

10. The method of claim 9  further comprising changing a source of the second data in response to sensing that chest compressions have commenced on the patient.

11. The method of claim 10  wherein changing the source of the second data comprises changing from SP02 to C02.

12. The method of claim 10  wherein changing the source of the second data comprises changing from a patient chemical measurement to a chest compression measurement.

13. The method of claim 12  wherein the chest compression measurement is displayed in the form of a bar graph.

14. The method of claim 13  wherein lengths of bars in the bar graph represent compression depths and spacing of bars in the bar graph represent compression rate.

15. The method of claim 14  further comprising displaying indicators for standard depth and rate with the bar graph.

16. The method of claim 1  wherein obtaining the data regarding chest compressions performed on the patient comprises obtaining measurements from an accelerometer that is positioned to move in coordination with the patient""s breastbone.

17. The method of claim 16  wherein determining a value for depth comprises double integrating measurements from the accelerometer.

18. The method of claim 1  wherein the accelerometer is attached to a housing that is in turn attached to a pair of defibrillator electrodes to be placed on the patient.

19. An external defibrillator  comprising:

one or more sensors arranged to contact a patient and obtain measurements regarding chest compressions performed on the patient;

a video display screen for displaying graphical representations regarding status of the patient and the defibrillator to a rescuer; and

a processor connected to memory that stores computer instructions for determining values of depth and rate of chest compressions performed on the patient and sensed by the sensors  and causing the video display screen to display indications of the determined values for depth and rate.

20. The external defibrillator of claim 19  wherein determining the values for depth and rate comprises determining numeric values in terms of distance for depth and compressions per minute for rate  and wherein displaying the indications of the determined values for depth and rate comprises displaying numbers that correspond to the determined numeric values.

21. The external defibrillator of claim 19  wherein the instructions are further provided to cause the video display screen to display an icon adjacent the indications of the determined values that indicates whether the chest compressions are being performed properly.

22. The external defibrillator of claim 21  wherein a color of the icon changes based on whether the chest compressions are being performed properly or improperly.

23. The external defibrillator of claim 1  wherein the instructions are further provided to cause the display on the video display screen an electrocardiogram of the patient with the determined values for depth and rate  in response to receiving information about the patient""s heart activity.

24. The external defibrillator of claim 23  wherein displaying the

electrocardiogram comprises moving an electrocardiogram trace laterally across the display

25. The external defibrillator of claim 24  wherein the instructions are further provided to cause the display on the video display screen of an unfiltered

electrocardiogram  and the subsequent display of a filtered electrocardiogram upon sensing that chest compressions have commenced on the patient.

26. The external defibrillator of claim 25  wherein the instructions are further provided to momentarily display on a trace of the electrocardiogram  an unfiltered portion showing compression artifacts  between another unfiltered portion and a filtered portion.

27. The external defibrillator of claim 19  wherein the instructions are further provided to display second data from the patient in coordination with the

electrocardiogram.

28. The external defibrillator of claim 27  wherein the instructions are further provided to change a source of the second data in response to sensing that chest compressions have commenced on the patient.

29. The external defibrillator of claim 28  wherein changing the source of the second data comprises changing from SP02 to C02.

30. The external defibrillator of claim 28  wherein changing the source of the second data comprises changing from a patient chemical measurement to a chest compression measurement.

31. The external defibrillator of claim 30  wherein the chest compression measurement is displayed in the form of a bar graph.

32. The external defibrillator of claim 31  wherein lengths of bars in the bar graph represent compression depths and spacing of bars in the bar graph represent compression rate.

33. The external defibrillator of claim 32  wherein the instructions are further provided to display indicators for standard depth and rate with the bar graph.

34. The external defibrillator of claim 19  wherein obtaining the data regarding chest compressions performed on the patient comprises obtaining measurements from an accelerometer that is positioned to move in coordination with the patient""s breastbone.

35. The external defibrillator of claim 34  wherein determining a value for depth comprises double integrating measurements from the accelerometer.

36. The external defibrillator of claim 19  wherein the one or more sensors comprise an accelerometer that is attached to a housing that is in turn attached to a pair of defibrillator electrodes to be placed on the patient.

37. An external defibrillator  comprising:

one or more sensors arranged to contact a patient and obtain measurements regarding chest compressions performed on the patient;

a video display screen for displaying graphical representations regarding status of the patient and the defibrillator to a rescuer; and

means for determining values of depth and rate of the chest compressions and for causing the video display screen to display indications of the determined values for depth and rate in response to receiving data from the one or more sensors that indicates the depth and rate of the chest compressions.