Abstract:
The present invention comprises a cardiopulmonary resuscitation (CPR) feedback device and a method for performing CPR. A chest compression detector device is provided that measures chest compression during the administration of CPR. The chest compression detector device comprises a signal transmitter operably positioned on the chest of the patient and adapted to broadcast a signal, and a signal receiver adapted to receive the signal. The chest compression detector device also comprises a processor, operably connected to the signal transmitter and the signal receiver. The processor repeatedly analyzes the signal received to determine from the signal a series of measurements of compression of the chest, and feedback is provided to the rescuer based on the series of measurements.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to devices and techniques useful for assisting in the administration of cardiopulmonary resuscitation (CPR). More particularly, the present invention relates to a device and method for using ultrasonic signals to determine the depth of chest compression during CPR. 
       BACKGROUND OF THE INVENTION 
       [0002]    CPR is a technique used by a rescuer in an emergency situation to get oxygen into a victims blood when that persons heart has stopped beating and/or they are not breathing spontaneously. When performing CPR the rescuer creates blood circulation in the victims body by periodically compressing the victims chest. 
         [0003]    The American Heart Association (AHA) recommends that the rescuer press down on the sternum with a force sufficient to depress it between 1.5 and 2.0 inches. The current recommended rate for these periodic depressions is 100 times a minute, and 30 chest compressions should be given for every two rescue breaths. Chest compressions produce blood circulation as the result of a generalized increase in intrathoracic pressure and/or direct compression of the heart. The guidelines state “blood circulated to the lungs by chest compressions will likely receive enough oxygen to maintain life when the compressions are accompanied by properly performed rescue breathing.” A victim can be kept alive using CPR provided the rescuer(s) are able to continue delivering properly performed chest compressions and rescue breaths. 
         [0004]    Administering CPR is a challenging and physically demanding procedure which is performed under stressful life and death circumstances. Performing chest compressions and rescue breaths is a also a physically demanding task, and can be difficult to properly coordinate. The quality of chest compressions and rescue breaths delivered to a patient can degrade for a number of reasons, including fatigue, lack of visual references, and rescue situation stresses. As rescuers become fatigued, they may not realize that they are compressing a patient&#39;s chest with inadequate force. The more fatigued a rescuer becomes, the less he may be compressing a patient&#39;s chest, and the more likely the effectiveness of the CPR is reduced. 
         [0005]    To be most effective, the rescuer must attempt to keep the chest compressions uniform both in terms of the time between successive chest compressions and the amount of force used for each compression. Keeping uniform intervals for chest compressions is difficult the longer the CPR must be administered as the stresses associated with a rescue situation can cause the rescuer&#39;s sense of time to be distorted. Keeping the chest compressions uniform in terms of force is difficult not only because of fatigue, but also because it is difficult for the rescuer to estimate the force being applied based on the distance which the chest is being compressed. Much of the difficulty in estimating the distance which the chest is being compressed stems from the relative position of the rescuer and the victim. When performing chest compressions, the rescuer positions his or her shoulders directly above the victim&#39;s chest, and pushes straight down on the sternum. In this position, the rescuer&#39;s line of sight is straight down at the victim&#39;s chest. With this line of sight, the rescuer has no visual reference point to use as a basis for estimating the distance that he or she is compressing the chest. 
         [0006]    The aforementioned problems may be compounded by a number of factors, such as when the length of time that CPR is being administered increases, and when the rescuer is not accustomed to rescue situations (for example when CPR is being performed by a lay person or a relatively inexperienced rescuer). 
         [0007]    A number of devices have been proposed to assist a rescuer in applying CPR, as described, for example, in U.S Pat. No. 6,125,299 to Groenke et al. Most of these devices measure either the force applied to a patient&#39;s chest, or measure the acceleration of the patient&#39;s chest (or rescuer&#39;s hand), or both. The measured force may be compared to a known desired value, and a prompt may be issued from the device instructing a rescuer to compress the patient&#39;s chest harder or softer. Displacement of a patient&#39;s chest can be calculated by double integrating a measured acceleration, and a prompt may be issued from the device instructing a rescuer to compress the patient&#39;s chest harder or softer. Many prior art devices also measure the frequency of chest compressions given, and are able to prompt a rescuer to increase or decrease the rate of compressions being administered. 
         [0008]    Although measuring acceleration is an acceptable method of determining chest compression during CPR, the method is not without its flaws. For example, signal error, external acceleration error, and drift error in the compression starting points can all create inaccuracies in chest compression measurement. External acceleration error can arise from use of the accelerometer in a moving vehicle such as an ambulance, or from unusual patient attitudes, such as partially sitting up. 
         [0009]    For these reasons, there is a need in the art for a practical device that more accurately measures the compression of a patient&#39;s chest during CPR, and provides feedback to a rescuer in the event that the displacement and frequency of chest compressions falls outside a preset criteria. A device of this type will provide rescuers with coaching which will enable them to deliver chest compressions consistently and beneficently. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention, through various embodiments, provides a cardiopulmonary resuscitation (CPR) feedback device and a method for performing CPR. In one embodiment, a chest compression detector device is provided that measures chest compression during administration of CPR. The chest compression detector device comprises a signal transmitter operably positioned on the chest of the patient and adapted to broadcast a signal, and a signal receiver adapted to receive the signal. The chest compression detector device also comprises a processor, operably connected to the signal transmitter and the signal receiver. The processor repeatedly analyzes the signal received to determine from the signal a series of measurements of compression of the chest, and feedback is provided to the rescuer based on the series of measurements. 
         [0011]    The CPR feedback device according to another embodiment is used in conjunction with an automatic external defibrillator (AED). The device includes a chest compression sensor on the chest of a patient, adapted to broadcast a signal toward the spine of a patient and adapted to receive a reflection of the signal. The chest compression sensor is in electrical communication with a control system of the AED, the control system processing a signal communicated from the chest compression sensor related to the magnitude of the chest compressions and to the frequency of chest compressions. The AED also includes a prompting means operably coupled to the AED control system for receiving communication signals from the AED control system and for communicating prompts to the rescuer for use by the rescuer in resuscitating the victim. The prompts are related to the signal communicated to the AED control system by the chest compression sensor. 
         [0012]    The present invention also comprises a method of performing cardiopulmonary resuscitation on a patient. The method includes the steps of providing a compression detection device proximate the sternum of the patient such that the device moves in unison with the chest of the patient during compression of the chest, broadcasting a signal from the compression detection device, receiving the signal at the compression detection device, compressing the chest of a patient, using a processor operably in communication with the compression detection device to determine from the signal a series of measurements of compression of the chest relative to the spine of the patient as the step of compressing the chest of the patient is performed, and automatically providing feedback to a rescuer performing the step of compressing the chest of the patient as part of cardiopulmonary resuscitation in response to the series of measurements that advises the rescuer whether the step of compressing the chest is being performed within a predetermined set of guidelines. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a perspective view of a chest compression detection device according to one embodiment of the present invention. 
           [0014]      FIG. 2  is a perspective view of a measurement device applied to a patient being used with an automatic external defibrillator according to one embodiment of the present invention. 
           [0015]      FIG. 3  is a perspective view of a measurement device being used on a patient. 
           [0016]      FIG. 4  is a side view of the measurement device applied to a patient. 
           [0017]      FIG. 5  is a perspective view of a rescue kit according to one embodiment of the present invention. 
           [0018]      FIG. 6  is a perspective view of a measurement device applied to a patient being used with an automatic external defibrillator according to one embodiment of the present invention. 
           [0019]      FIG. 7  is a perspective view of a measurement device applied to a patient being used with an automatic external defibrillator according to one embodiment of the present invention. 
           [0020]      FIG. 8  is a block diagram of an automatic external defibrillator. 
           [0021]      FIG. 9  is a perspective view of a sensor for use with an embodiment of the present invention. 
           [0022]      FIG. 10  is a perspective view of an automatic external defibrillator incorporating a measurement device within a pair of electrodes according to one embodiment of the present invention. 
           [0023]      FIG. 11  is a side view of the measuring device applied to a patient according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    In the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as to not unnecessarily obscure aspects of the present invention. 
         [0025]    Referring to  FIGS. 1-5 , a chest compression detection device  10  is depicted. Device  10  includes a signal transmitter  14 , a signal receiver  16 , and a processor  18 . In one embodiment, device  10  comprises an ultrasonic transducer. Transmitter  14  and receiver  16  are integrated into device  10 . Processor  18  is operably coupled to both transmitter  14  and receiver  16 . Processor  18  instructs transmitter  14  to send out an ultrasonic pulse  20 , then counts the elapsed time for pulse  20  to reach receiver  16 . Processor  18  can then calculate the distance of an object from device  10 . Device  10  further includes an audio speaker  26 , a power source  28 , and may include a communicator  30 . Power source  28  provides electrical power to all components in device  10 . 
         [0026]    Device  10  is placed on a victim&#39;s chest  22 , in the location where chest compressions are to be administered. In one embodiment, device  10  is preferably located on the victim&#39;s sternum, generally between the victim&#39;s nipples, and in line with a victim&#39;s spine  24 . A rescuer places his hands over device  10  and begins to administer chest compressions. Processor  18  instructs transmitter  14  to emit ultrasonic pulses  20 . Pulses  20  are directed towards victim&#39;s spine  24 , reflected, and received by receiver  16 . Processor  18  counts the time it takes for pulse  20  to travel from transmitter  14  to receiver  16 . Knowing the velocity at which sound waves travel, processor  18  can then calculate the distance that pulse  20  traveled. By collecting data of the distance traveled by many successive pulses, processor  18  can determine the amount that a chest  22  is being compressed by a rescuer. In one embodiment, the number of pulses  20  emitted per second is sufficient to give processor  18  sufficient data to accurately calculate chest compression depth. Once processor  18  has calculated chest compression depth, processor  18  compares that depth to a desired range of compression depth. 
         [0027]    In order for CPR to be effective, chest compressions are preferably between one and one half (1.5) inches and two (2) inches. In the event that processor  18  determines chest  22  is not being compressed enough, processor  18  is adapted to provide feedback to the rescuer preferably through speaker  26 . Similarly, if processor  18  determines that chest  22  is being over-compressed, processor  18  uses speaker  26  to provide feedback to the rescuer. Such feedback may be in the form of a voice prompt stating “push harder” in the event of under-compression of chest  22 , or “push softer” in the event of over-compression of chest  22 . Such feedback may also be some other audible prompt, such as beeps, or may include visual instructions, tactile feedback, or any combination thereof. 
         [0028]    Processor  18  is also adapted to monitor the rate at which compressions are given and provide feedback to a rescuer if the rate of chest compressions falls outside of a predetermined range of rates. If the rate of chest compressions being delivered by the rescuer is less than the desired range, processor  18  causes speaker  26  to provide feedback to the rescuer, such as with a voice prompt stating “push faster,” or other feedback prompt. If the rate of chest compressions being delivered by the rescuer is greater than the desired range, processor  18  causes speaker  26  to provide feedback to the rescuer, such as with a voice prompt stating “push slower,” or other feedback prompt. It should be apparent that audio speaker  26  may be supplemented with, or replaced by, various indicators such as lights, a visual display, vibrating mechanism, and so on. 
         [0029]    In another embodiment of the present invention depicted in  FIG. 2 , device  10  does not include a speaker, rather device  10  includes a communicator  30 . Communicator  30  is adapted to communicate chest compression data to automatic external defibrillator (AED)  12 , using wireless means such as acoustic signals, optical signals, Bluetooth, IR, or RF, AED  12  includes an audio speaker  32  and/or a visual display  34 . Audio speaker  32  and visual display  34  are each adapted to provide feedback to a rescuer in response to the chest compression data received from communicator  30  of device  10 . 
         [0030]    In such an embodiment, device  10  may comprise part of a rescue kit  36 , depicted in  FIG. 5 . Rescue kit  36  may include basic first aid items such as a face shield, rubber gloves, scissors, and so on, in addition to a chest compression detection device. Because AED units are relatively expensive, it may be cost prohibitive to equip a large building or area with a sufficient number of AEDs to ensure the close proximity of an AED to a cardiac arrest victim. However, a large building or area may be outfitted with many lower cost rescue kits  36 . In the case of a rescue attempt on a victim, a first rescuer can quickly obtain a rescue kit  36  and begin CPR with device  10  while a second rescuer can retrieve an AED  12  from a central location in the building or area. As AED  12  gets into communication range with device  10 , device  10  and AED  12  begin communicating via communicator  30 . AED  12  can then immediately begin providing prompts to a first rescuer using audio speaker  32  and/or visual display  34 . Once first electrode  38  and second electrode  40  of AED  12  are attached to a victim, AED  12  may also prompt a rescuer using audio speaker  32  and/or visual display  34  to momentarily cease chest compressions while a defibrillation shock is administered. 
         [0031]    In another embodiment of the present invention depicted in  FIG. 6 , a chest compression detection device  110  is provided as part of an AED  112 . Device  110  is removably coupled to AED  112  with wires  140 . AED  112  includes a first electrode  115 , a second electrode  117 , and a processor  118  as depicted in  FIG. 8 . Device  110  includes a transmitter  114  and a receiver  116 , whereby device  110  is adapted to emit ultrasonic pulse  20  from transmitter  114  into a patient&#39;s chest  122  and receive pulse  20  at receiver  116  subsequent to pulse  20  being reflected off a patient&#39;s spine  24 , as shown in  FIG. 4 . The time elapsed between the transmitting and the receiving of a pulse  20  is used by processor  118  to calculate the distance traveled by pulse  20 . By collecting data of the distance traveled by many successive pulses, processor  118  can determine the distance that a chest  122  is being compressed. In one embodiment, the number of pulses  20  emitted per second is sufficient to give processor  18  sufficient data to accurately calculate chest compression depth. 
         [0032]    Once processor  118  has calculated chest compression depth, processor  118  compares that depth to a desired range of compression depth (ideally between one and one half (1.5) inches and two (2) inches.) If processor  118  determines that chest  122  is not being compressed enough, processor  118  causes AED  112  to provide feedback to a rescuer performing chest compressions. The prompt may be a voice prompt stating “push harder,” or other feedback prompt using an audio speaker  126 , or may be a visual prompt using visual display  128 , or both. If processor  118  determines that chest  122  is being compressed too much, feedback may be provided to the rescuer with a voice prompt stating “push softer” using speaker  126 , or a visual prompt using visual display  128 , or both. 
         [0033]    Processor  118  is also adapted to monitor the rate at which chest compressions are given, and provide feedback to a rescuer if the rate of chest compressions falls outside of a predetermined range of rates. If the rate of chest compressions being delivered by the rescuer is less than the desired range, processor  118  causes AED  112  to provide feedback to the rescuer to increase the rate of compressions. Such feedback may be a voice prompt stating “push faster,” or other audible prompt from speaker  126 , a visual prompt provided by visual display  128 , or other feedback. If the rate of chest compressions being delivered by the rescuer is greater than the desired range, processor  118  causes AED  112  to provide feedback to the rescuer to decrease the rate of compressions. Such feedback may be a voice prompt stating “push slower,” or other audible prompt from speaker  126 , a visual display provided by visual display  128 , or other feedback. In an alternative embodiment depicted in  FIG. 7 , device  110  lacks wires  140 , but includes a wireless means for transmitting data to AED  112 , such as, for example, a wireless communicator  130 , wherein said wireless means may employ acoustic signals, optical signals, Bluetooth, IR, or RF. 
         [0034]    In one embodiment, AED  112  includes an electrical system such as that disclosed in U.S. Pat. No. 6,125,299 to Groenke et al., which is hereby incorporated by reference.  FIG. 8  is a block diagram of electrical system  70  of AED  112 . A digital microprocessor-based control system  72  is used for controlling overall operation of AED  112  and for delivering a defibrillation shock pulse through electrodes  115  and  117  via connector  67  and lead wires. The electrical control system  72  further includes an impedance measuring circuit for testing the interconnection and operability of electrodes  115  and  117  to detect several faults. Control system  72  includes a processor  118  interfaced to program memory  76 , data memory  77 , event memory  78  and real time clock  79 . The operating program executed by processor  118  is stored in program memory  76 . Electrical power is provided by the battery  80  which is removably positioned within the battery compartment of AED  112  and is connected to power generation circuit  84 . 
         [0035]    Power generation circuit  84  is also connected to lid switch  90 , watch dog timer  92 , real time clock  79  and processor  118 . Lid switch  90  such as, for example, a Hall-effect or magnetic read relay switch, provides signals to processor  118  indicating whether the lid of AED  112  is open or closed. Data communication port  64  is coupled to processor  118  for two-way serial data transfer using an RS-232 protocol. Rescue switch  63 , maintenance indicator  61 , the indicator lights of diagnostic display panel  62 , the voice circuit  94  and piezoelectric audible alarm  96  are also connected to processor  118 . Voice circuit  94  is connected to speaker  126 . In response to voice prompt control signals from processor  118 , circuit  94  and speaker  126  generate audible voice prompts for consideration by a rescuer. 
         [0036]    High voltage generation circuit  86  is also connected to and controlled by processor  118 . Circuits such as high voltage generation circuit  86  are generally known, and disclosed, for example, in the commonly assigned Persson et al. U.S. Pat. No. 5,405,361, which is hereby incorporated by reference. In response to charge control signals provided by processor  118 , high voltage generation circuit  86  is operated in a charge mode during which one set of semiconductor switches (not separately shown) cause a plurality of capacitors (also not shown), to be charged in parallel to the  12 V potential supplied by power generation circuit  84 . Once charged, and in response to discharge control signals provided by processor  74 , high voltage generation circuit  86  is operated in a discharge mode during which the capacitors are discharged in series by another set of semiconductor switches (not separately shown) to produce the high voltage defibrillation pulses. The defibrillation pulses are applied to the patient by electrodes  115  and  117  through connector  67  connected to the high voltage generation circuit  86 . 
         [0037]    Impedance measuring circuit  66  is connected to both connector  67  and real time clock  79 . Impedance measuring circuit  66  is interfaced to processor  118  through analog-to-digital (A/D) converter  69 . Impedance measuring circuit  66  receives a clock signal having a predetermined magnitude from clock  79 , and applies the signal to electrodes  115  and  117  through connector  67 . The magnitude of the clock signal received back from electrodes  115  and  117  through connector  67  is monitored by impedance measuring circuit  66 . An impedance signal representative of the impedance present across electrodes  115  and  117  is then generated by circuit  66  as a function of the ratio of the magnitudes of the applied and received clock signals (i.e., the attenuation of the applied signal). 
         [0038]    For example, if electrodes  115  and  117  within an unopened electrode package are connected by the lead wires and connector  68  is properly connected to connector  67  on AED  112 , a relatively low resistance (e.g., less than about 10 ohms) is present across electrodes  115  and  117 . If the hydrogel adhesive on electrodes  115  and  117  is too dry, or the electrodes  115  and  117  are not properly positioned on the patient, a relatively high resistance (e.g., greater than about two hundred fifty ohms) will be present across the electrodes  115  and  117 . The resistance across electrodes  115  and  117  will then be between about twenty-five and two hundred fifty ohms when fresh electrodes  115  and  117  are properly positioned on the patient with good electrical contacts. It should be noted that these resistance values are given as exemplary ranges and are not meant to be absolute ranges. The impedance signal representative of the impedance measured by circuit  66  is digitized by A/D converter  69  and provided to processor  118 . 
         [0039]    Impedance measuring circuit  65  is connected to connector  67  and real time clock  79 , and is interfaced to processor  118  through analog-to-digital (A/D) converter  69 . Impedance measuring circuit  65  receives a clock signal having a predetermined magnitude from clock  79 , and applies the signal to chest compression detection device  110  through connector  67 . The magnitude of the clock signal received back from device  110  through connector  32  is monitored by impedance measuring circuit  65 . An impedance signal representative of the impedance present across device  110  is then generated by impedance measuring circuit  65  as a function of the ratio of the magnitudes of the applied and received clock signals (i.e., the attenuation of the applied signal). The impedance signal representative of the impedance measured by circuit  65  is digitized by A/D converter  69  and provided to processor  118 . 
         [0040]    Referring now to  FIG. 9 , the present invention may also incorporate a pulse oximetry sensor  142 . Sensor  142  is operably coupled to AED  112 , and is placed on a victim&#39;s fingertip, earlobe, or other relatively thin part of a victim&#39;s body. Sensor  142  utilizes selected wavelengths of light to noninvasively determine the saturation of oxyhemoglobin (SpO 2 ) in a victim&#39;s blood. Based on SpO 2  levels, an estimate of the oxygen content of a victim&#39;s blood can be determined. Sensor  142  is utilized while chest compressions are administered by a rescuer. Processor  118  receives information from sensor  142 , and compares oxygen level readings to a desired range of oxygen levels. Low oxygenation may be due to not compressing the chest of a victim far enough, or at a fast enough rate. In the event that oxygen levels from sensor  142  are too low, processor  118  causes AED  112  to provide feedback to the rescuer to increase the depth of, or rate of compressions. Such feedback may be a voice prompt from speaker  126  stating “push harder” or “push faster,” a visual prompt provided by visual display  128 , or other feedback. Conversely, high oxygenation may be due to compressing the chest of a victim too far, or at too fast of a rate. In the event that oxygen levels from sensor  142  are too high, processor  118  causes AED  112  to provide feedback to decrease the depth of, or rate of compressions. Such feedback may be a voice prompt from speaker  126  stating “push softer” or “push slower,” a visual prompt provided by visual display  128 , or other feedback. 
         [0041]    Referring now to  FIG. 10 , a further embodiment of the present invention is shown. Rescuers may be reluctant to conduct chest compressions while putting their hands on an electric device, out of fear of electrocution. Although accidental electrocution is highly improbable, the embodiment depicted in  FIG. 10  does not require a rescuer to conduct chest compressions while pushing on an electronic chest compression detection device. Rather, first electrode  115  is adapted to include a signal transmitter  114 , and second electrode  117  is adapted to include a signal receiver  116 . First electrode  115  and second electrode  117  are operably coupled to processor  118  in AED  112 . Pulse  20  (not shown) is emitted from transmitter  114  in first electrode  115 , triangulated off of spine  124 , and received by receiver  116  in second electrode  117 . Electrodes  115  and  117  may be placed on a victim&#39;s chest  122  as shown in  FIG. 10 . 
         [0042]    Alternatively, one electrode may be placed on a victim&#39;s chest  122  generally over the heart, while the other electrode is placed on a victim&#39;s back, such that the two electrodes and the heart are inline, as shown in  FIG. 11 . In such an arrangement, transmitter  114  in electrode  115  directs a pulse  20  towards receiver  116  in electrode  117 , and pulse  20  is not reflected before being received. Further, those skilled in the art will readily recognize that electrodes  115  and  117  and/or chest compression detection device  110  may be placed in locations on a patient other than those explicitly shown in the figures or described herein without deviating from the spirit or scope of this invention. 
         [0043]    In order to enhance the reflectivity of pulse  120 , a reflector pad may be used in conjunction with all embodiments of the present invention. The reflector pad may be placed generally proximate the victim&#39;s back and is adapted to increase the reflectivity of pulse  120 , and thereby increase the ability of receiver  116  to receive the reflected pulse  120 . 
         [0044]    The present invention may be embodied in other specific forms without departing from the essential attributes thereof, therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.