CPR COACHING DEVICE HAVING INTERNAL SENSOR FOR SENSING A PHYSIOLOGICAL CHARACTERISTIC

[001] The invention relates generally to medical devices, and more particularly, to cardio-pulmonary resuscitation (CPR) coaching and training devices.

[002] Cardiac arrest is a life-threatening medical condition in which the patient's heart fails to provide blood flow to support life. CPR can be administered to a patient experiencing cardiac arrest to cause blood to flow in the patient. A rescuer administers CPR by compressing the patient's chest interspersed with blowing into the patient's mouth to fill the lungs with oxygen. CPR can be combined with other forms of therapy as well, such as defibrillation therapy. As is known, during cardiac arrest, the electrical activity of the heart may be disorganized (ventricular fibrillation, "VF"), too rapid (ventricular tachycardia, "VT"), absent (asystole), or organized at a normal or a slow heart rate without producing blood flow (pulseless electrical activity). A defibrillation shock delivered to a patient suffering from VF or VT can stop the unsynchronized or rapid electrical activity and allow a normal sinus rhythm to return. Between the times defibrillation shocks are delivered to a patient, CPR is administered to promote blood flow.

[003] Studies have suggested that a patient's survival prospects can be improved by the administration of high-quality CPR. The quality of the CPR is directly related to the quality of the chest compressions, a part of which is determined by compression depth. That is, good chest compressions are generally those which depress the chest of an adult by four centimeters and about two and a half centimeters for a child. There are many guidelines known in the art that set out desired compression depths for CPR. Learning to administer chest compressions of sufficient depth is traditionally part of CPR training. For example, in practice situations involving manikins, compression depth is commonly measured and the information fed back to the participant. It is assumed that by practicing chest compressions on a manikin, the participant will be capable of repeating the same movement pattern on real human patients. However, studies have shown that the ability to repeat the movement pattern of administering chest

compressions is poor even immediately after being trained, and not surprisingly, becomes worse over time. Additionally, since human anatomy varies from person to person, patients have differing degrees of resistance to chest compressions and require different levels of force to sufficiently compress the chest. As a result, learning to administer chest compressions of uniform, correct compression depth through CPR training on a manikin is difficult to achieve.

[004] To assist a rescuer in administering CPR with chest compressions of sufficient depth, various devices have been developed that can be used during CPR to provide a rescuer with CPR coaching. These devices are typically placed on the chest of the patient, and the rescuer's hands are in turn placed on the device when delivering a downward force to compress the patient's chest. As the device moves with the compression of the chest, the device measures a force or a characteristic of the movement, such as acceleration, to determine sufficient compression depth. Based on the measurement, visual feedback, audible feedback, tactile feedback or a combination thereof are provided to the rescuer on the sufficiency of the chest compression. For example, U.S. Patent Application Publication No. 2006/0019229 describes a device that emits a sound when the chest compression is performed with a force that exceeds a predetermined value. The device optionally also emits a sound indicating the intended frequency of chest compressions for correct pacing. Another example is described in U.S. Patent No. 6,306,107, which describes a device that includes an accelerometer, a force activated switch, and a calculation unit. The device is positioned on the patient's chest during CPR to register parameters such as depression distance, duration or rate of depressions during chest compression. Visual feedback on the depth of the compressions is provided to the rescuer by light-emitting diodes (LEDs) or both visual and audible feedback are provided by way of a display unit having a screen and loudspeaker.

[005] CPR coaching has also been integrated into a defibrillator as well. Examples of a defibrillator with CPR coaching are shown in U.S. Patent No. 6,125,299, U.S. Patent No. 6,351,671, and also described in previously discussed U.S. Patent No. 6,306,107.

The '299 and '671 patents both describe a force sensor which is placed on the patient's chest and to which chest compressions are applied. The force sensor is connected to a defibrillator which senses the applied force of the chest compressions and, using the defibrillator's audible prompts, coaches the rescuer to press "harder" or "softer" or "faster" or "slower." The '107 patent, as previously discussed, describes a compression pad with an accelerometer instead of a force sensor which senses the depth of the chest compressions rather than their force. The approach described in the '107 patent is preferable as CPR guidelines are directed to the depth of compression rather than the applied force, which does not always correlate with compression depth due to different chest resistances to CPR compression.

[006] Conventional CPR coaching devices have been designed with sensors that detect physiological characteristics of a patient. However, the conventional designs position the sensor at a location away from the general location where chest compression forces are applied to compress the patient's chest. For example, in U.S. Patent Application Publication No. 2001/0047140, an integrated resuscitation pad is described as providing CPR coaching and includes a pulse detection system. The pulse detection system, however, is located away from where chest compression forces are applied because a force sensing device is located there instead to sense the force and timing of the chest compressions. The location of the pulse detection system requires the integrated resuscitation pad to extend over a region of the patient' s chest away from where chest compressions are applied, which results in a much larger pad. In the event the integrated resuscitation pad of the aforementioned U.S. patent application is to be used on a patient having a smaller torso than that for which it is designed, the pulse detection system may be located at a position on the patient's chest (i.e., away from the patients centerline) that reduces the ability of the sensor to accurately detect the physiological characteristic intended to be sensed, consequently, defeating the purpose of including the sensor in the integrated resuscitation pad.

[007] In accordance with the principles of the present invention a cardiac therapy system is provided having a CPR coaching device and a defibrillator. The CPR

coaching device is operable to coach a rescuer in administering CPR to a patient. The CPR coaching device has a housing that includes an upper portion and a lower portion. The upper portion is configured for placement of at least one of the rescuer' s hands for delivery of chest compression force to the patient and the lower portion configured to be placed against the patient's chest. The CPR coaching device further has a physiological sensor located within the housing that is positioned between the upper and lower portions of the housing. The physiological sensor is operable to sense a physiological characteristic of the patient. The defibrillator is coupled to the CPR coaching device and is operable to obtain ECG signals through electrodes and is further operable to deliver a defibrillating shock through the electrodes. The defibrillator is also operable to receive from the CPR coaching device signals representative of the physiological characteristic sensed by the physiological sensor.

[008] Another aspect of the invention provides a defibrillation system having a defibrillator and a CPR coaching device. The defibrillator is configured to measure an ECG of a patient and is further configured to deliver defibrillation energy to the patient. The CPR coaching device is coupled to the defibrillator and is configured to coach a rescuer in delivering CPR to the patient. The CPR coaching device includes a sensor configured to sense a physiological characteristic of the patient. The CPR coaching device has a non-conductive lower surface configured to be placed against the patient' s chest and further configured to be electrically insulated from the patient.

[009] Another aspect of the invention provides a method of obtaining physiological information of a patient. The method includes attaching electrodes of a defibrillator to a patient. The defibrillator is operable to measure an ECG of the patient and is further configured to deliver defibrillation energy to the patient. The method further includes attaching a CPR coaching device to the patient that is coupled to the defibrillator and operable to assist a rescuer in administering CPR to the patient. An ECG of the patient is obtained and a physiological characteristic of the patient is sensed by a sensor located in the CPR coaching device. The CPR coaching device has the sensor disposed between a lower surface configured to be placed against the patient' s chest and an upper

surface to which chest compression force is applied. Information related to the sensed physiological characteristic is obtained and transferred to the defibrillator. In the drawings:

[010] FIGURE 1 is a diagram of a CPR coaching device according to an embodiment of the present invention.

[011] FIGURE 2 illustrates a rescuer using a CPR coaching device and defibrillator according to an embodiment of the present invention.

[012] FIGURE 3 is a simplified block diagram of components included in a CPR coaching device according to an embodiment of the present invention.

[013] FIGURE 4 is a simplified block diagram of a defibrillator to which the CPR coaching device is coupled according to an embodiment of the present invention.

[014] FIGURE 5 is a diagram of a CPR coaching device coupled to a defibrillator according to another embodiment of the present invention.

[015] Certain details are set forth below to provide a sufficient understanding of the invention. However, it will be clear to one skilled in the art that the invention may be practiced without these particular details. Moreover, the particular embodiments of the present invention described herein are provided by way of example and should not be used to limit the scope of the invention to these particular embodiments. In other instances, well-known circuits, control signals, timing protocols, and software operations have not been shown in detail in order to avoid unnecessarily obscuring the invention.

[016] FIGURE 1 illustrates a CPR coaching device 100 according to an embodiment of the present invention. The CPR coaching device 100 is operable to coach a rescuer in administering CPR to a patient, such as providing feedback on whether chest compressions are of sufficient depth and whether the pace of the chest compression is adequate. In addition to providing CPR coaching to a rescuer, the CPR coaching device 100 includes a sensor for sensing a physiological characteristic, such as a patient's pulse, of the patient to whom the CPR coaching device 100 is attached and to whom CPR is being administered by the rescuer. Including a sensor in the CPR coaching

device 100 takes advantage of its position on the patient's chest to sense and gather physiological information related to the sensed physiological characteristic. The same information can then be used in conjunction with other acquired physiological information to create a more specific resuscitation protocol for that particular patient.

[017] An upper portion 120 of a housing 118 of the CPR coaching device 100 is shown in FIGURE 1. An illustration 110 depicting a patient's torso is included on the upper portion 120 of the CPR coaching device 100 to illustrate the position and orientation of the CPR coaching device 100 on the patient. In this position the lower portion of the device 100 opposite the upper portion 120 is in contact with the torso of the patient. A cable 130 is used to transfer the physiological information to a medical device, such as a defibrillator, to which the CPR coaching device 100 is attached.

[018] As shown in FIGURE 2, with the CPR coaching device 100 attached to the sternum of a patient 210, a rescuer 220 prepares to apply CPR chest compressions in a conventional manner using two hands with one placed over the other. Instead of placing the hands directly on the patient 210, the CPR coaching device 100 is directly compressed by the rescuer 220, and chest compressions are applied to the patient 210 via the CPR coaching device 100. Chest compressions are administered by the rescuer 220 as prescribed by conventional CPR protocols. The CPR coaching device is attached to the patient 210 by an adhesive layer 128 present on a lower portion 124 of the housing 118 (FIGURE 3) of the CPR coaching device 100. The lower portion 124 is configured to be placed against the patient' s chest and does not have any electrodes that are electrically coupled to the patient. The lower portion 124 can be made from a material that electrically insulates the CPR coaching device 100 from the patient.

[019] As will be described in more detail below, in various embodiments of the invention the adhesive layer 128 is formed from a material that also provides an acoustic coupling medium, such as hydrogel.

[020] As also shown in FIGURE 2, a defibrillator 310 is attached to the patient 210 by electrodes 316. The defibrillator 310, as known, can be used to deliver defibrillating shocks to the patient 210 suffering from cardiac arrest. More specifically, the

defibrillator can deliver a high-voltage impulse to the heart in order to restore normal rhythm and contractile function in patients who are experiencing arrhythmia, such as VF or VT that is not accompanied by spontaneous circulation. There are several classes of defibrillators, including manual defibrillators, implantable defibrillators, and automatic external defibrillators (AEDs). AEDs differ from manual defibrillators in that AEDs can automatically analyze the electrocardiogram (ECG) rhythm to determine if defibrillation is necessary. In nearly all AED designs, the user is prompted to press a shock button to deliver the defibrillation shock to the patient when a shock is advised by the AED.

[021] The electrodes 316 are applied across the chest of the patient 210 by the rescuer

220 in order to acquire an ECG signal from the patient's heart. The defibrillator 310 then analyzes the ECG signal for signs of arrhythmia. If VF is detected, the defibrillator 310 signals the rescuer 220 that a shock is advised. After detecting VF or other shockable rhythm, the rescuer 220 then presses a shock button on the defibrillator 310 to deliver defibrillation pulse to resuscitate the patient 210. The CPR coaching device 100 is coupled to the defibrillator 310 by the electrical cable 130 to provide the defibrillator 310 with physiological information obtained by sensors contained in the CPR coaching device 100.

[022] FIGURE 3 illustrates a simplified block diagram of various components included in the CPR coaching device 100 according to an embodiment of the invention. A CPR compression sensor 352 included in the CPR coaching device 100 senses characteristics related to chest compressions being applied to the patient 210. For example, in one embodiment the CPR compression sensor 352 is an accelerometer that is operable to detect and measure acceleration of the CPR coaching device 100 during administration of chest compressions. In another embodiment, the CPR compression sensor 352 is a force sensor that measures the force of the chest compressions. As previously described, the measured acceleration and measured force can be used to gauge the sufficiency of the chest compressions applied by the rescuer 220. The CPR compression sensor 352 generates output signals CPRSENSE in response to sensing the

chest compression related characteristic. The CPRSENSE signals generated by the CPR compression sensor 352 are indicative of the measured characteristic related to the chest compressions, such as measured acceleration or force.

[023] A calculation and control unit 354 is coupled to receive the CPRSENSE signals from the CPR compression sensor 352. The calculation and control unit 354 includes processing and calculation circuitry known in the art that is operable to determine the sufficiency of the chest compressions from the CPRSENSE signals. For example, in the case of an acceleration measurement and the CPRSENSE signals represent the acceleration of the CPR coaching device 100 during chest compressions, the calculation and control unit 354 is programmed to perform double-integration to calculate a displacement of the CPR coaching device 100. As previously discussed, the calculated displacement can be used to determine if the chest compressions are of sufficient depth. In other embodiments of the invention, the calculation and control unit 354 is further operable to determine a pace (rate) of the chest compressions being administered from the CPRSENSE signals.

[024] Based on the determination from the CPRSENSE signals, the calculation and control unit 354 generates control signals CNTRL that are provided to a CPR feedback device 356. The CNTRL signals control the CPR feedback device 356 to provide feedback to the rescuer 220 administering the chest compressions. For example, in various embodiments of the invention, the CPR feedback device 356 is a visual display device for providing visual feedback to the rescuer 220. In other embodiments the CPR feedback device is alternatively or additionally an audio device for providing audible feedback to the rescuer 220. The visual and/or audible feedback is provided to coach the rescuer 220 on whether the depth of the chest compressions is sufficient, for example, too deep, not deep enough, or within a range of acceptable depth. Where the calculation and control unit 354 is further operable to determine the pace of the chest compressions, the CNTRL signals include signals to control the CPR feedback device 356 to further coach the rescuer 220 on the pace of the chest compressions, such as, coaching the rescuer to administer the chest compressions faster or slower.

[025] The CPR coaching device 100 further includes a physiological sensor 360 that is operable to sense a physiological characteristic of the patient 210 and generate output signals PHYSENSE that are indicative of sensed physiological information. The physiological sensor 360 is positioned in the CPR coaching device 100 between the upper portion 120 to which chest compression force is applied and the lower portion 124 that is placed against the patient's chest. By positioning the physiological sensor 360 in the CPR coaching device 100 in this manner, the sensor 360 is advantageously positioned for sensing a physiological characteristic, such as the patient's cardiac circulation.

[026] In various embodiments, the physiological sensor 360 is an ultrasonic transducer operable to detect sounds from pulmonary system operation, such as heart sounds and lung sounds. In other embodiments of the invention, the physiological sensor 360 is an acoustic transducer operable to detect sounds from pulmonary system operation. In the embodiments where the physiological sensor 360 operates according to acoustic principles, the adhesive layer 128 is formed from an adhesive material that also has properties for acoustically coupling the physiological sensor 360 to the patient 210. In other embodiments of the invention, the physiological sensor 360 is a sensor for a pulse oximetry system that provides non-invasive measurement of functional oxygen saturation of the patient's blood (SpO ₂ ) and/or pulse frequency. In other embodiments the physiological sensor 360 detects chemistry of the body such as electrolyte content of perspiration. In other embodiments of the invention, the physiological sensor 360 is a motion sensor that is operable to detect pulse motion in the patient 210. An example of such a sensor is an accelerometer that is calibrated to detect movement resulting from the patient's pulse.

[027] In the previously described embodiments, the sensors and related circuitry are conventional and can be implemented using designs and operations known by those ordinarily skilled in the art. Additionally, various combinations of the previously described sensors can be included in the CPR coaching device 100.

[028] The PHYSENSE signals are received by the calculation and control unit 354 and in turn provided as physiological information signals PHYINFO to a medical device, such as a defibrillator 310 (FIGURE 2), via cable 130. In various embodiments, the calculation and control unit 354 processes the PHYSENSE signals before providing the same to the medical device, for example, performing signal processing, performing calculations to derive information from the PHYSENSE signals, and the like. The resulting information is then transmitted to the medical device as part of the PHYINFO signals.

[029] FIGURE 4 illustrates various components included in the defibrillator 310

(FIGURE 2) to which the CPR coaching device 100 is coupled through cable 130. The defibrillator 310 is designed for small physical size, light weight, and relatively simple user interface capable of being operated by personnel without high training levels or who otherwise would use the defibrillator 310 only infrequently. In contrast, a paramedic or clinical (manual) defibrillator of the type generally carried by an emergency medical service (EMS) responder tends to be larger, heavier, and have a more complex user interface capable of supporting a larger number of manual monitoring and analysis functions and protocol settings.

[030] An ECG front end circuit 202 is connected to the electrodes 316 that are connected across the chest of the patient 210. The ECG front end circuit 202 operates to amplify, buffer, filter and digitize an electrical ECG signal generated by the patient' s heart to produce a stream of digitized ECG samples. The digitized ECG samples are provided to a controller 206 that performs an analysis to detect VF, shockable VT or other shockable rhythm. If a shockable rhythm is detected, the controller 206 sends a signal to HV (high voltage) delivery circuit 208 to charge a high voltage capacitor of circuit 208 in preparation for delivering a shock, and a shock button on a user interface 214 is activated to begin flashing. The rescuer 220 is then advised by an audible instruction to keep away from the patient 210 ("hands off instruction). When the rescuer 220 presses the shock button on the user interface 214 a defibrillation shock

is delivered from the HV delivery circuit 208 to the patient 210 through the electrodes 316.

[031] The controller 206 is coupled to further receive input from a microphone 212 to produce a voice strip. The analog audio signal from the microphone 212 is preferably digitized to produce a stream of digitized audio samples which may be stored as part of an event summary 134 in a memory 218. The user interface 214 may consist of a display, an audio speaker, and control buttons such as an on-off button and a shock button for providing user control as well as visual and audible prompts. A user interface of the present invention may also include one or more control buttons for selecting a rescue protocol stored in memory 218 to be carried out during a rescue. A clock 216 provides real-time or elapsed time clock data to the controller 206 for time- stamping information contained in the event summary 134. The memory 218, implemented either as on-board RAM, a removable memory card, or a combination of different memory technologies, operates to store the event summary 134 digitally as it is compiled during the treatment of the patient 210. The event summary 134 may include the streams of digitized ECG, audio samples, and other event data as previously described.

[032] The defibrillator 310 further includes a CPR coaching device interface 140 that couples the CPR coaching device 100 to the defibrillator 310 and through which the PHYINFO signals are received by the controller 206. The coaching device interface 140 receives the PHYINFO signals from the CPR coaching device 100 and prepares the signals for use by the controller 206. For example, as previously described, the physiological information obtained by the CPR coaching device 100 can be used by the defibrillator 310 in determining an appropriate resuscitation protocol. For example, prior to delivering a shock to the patient, the controller 206 is operable to determine whether a patient pulse is present based on information sensed by the physiological sensor 360 and the PHYSENSE signals generated by the same. Pulse information along with ECG information can be considered by the controller 206 in determining an appropriate resuscitation protocol. As known, the form of therapy to be provided to a

patient without a detectable pulse depends, in part, on an assessment of the patient's cardiac condition. The rescuer 220 may apply a defibrillation shock to the patient 210 experiencing ventricular fibrillation VF or VT to stop the unsynchronized or rapid electrical activity and allow a perfusing rhythm to return, as previously described. However, if the patient lacks a detectable pulse and is experiencing asystole or pulseless electrical activity (PEA), defibrillation should not be applied and the rescuer 220 should perform CPR instead, which causes some blood to flow in the patient 210. In the event the controller determines from the ECG information and the physiological information obtained by the CPR coaching device 100 that the patient 210 is experiencing asystole or PEA, instructions to not administer a defibrillation shock and instead perform CPR can be issued over the user interface 214, such as in the form of audible or visual instructions.

[033] FIGURE 5 illustrates the CPR coaching device 100 coupled through cable 130 to the defibrillator 310. The defibrillator 310 represents a semi-automatic external defibrillator (AED). FIGURE 5 illustrates a particular embodiment of a defibrillation system having an AED 310. However, other types of defibrillators can be used as well. The AED 310 is housed in a rugged polymeric case 312 which protects the electronic circuitry inside the case, which was previously described with reference to FIGURE 4, and also protects the rescuer 220 user from shocks. Attached to the case 312 by electrical leads are a pair of electrode 316. The electrode 316 are in a cartridge 314 located in a recess on the top side of the AED 310. The electrode pads are accessed for use by pulling up on a handle 317 which allows removal of a plastic cover over the electrode 316. The user interface is on the right side of the AED 310. A small ready light 318 informs the rescuer 220 of the readiness of the AED 310. In this embodiment the ready light blinks after the AED 310 has been properly set up and is ready for use. The ready light is on constantly when the AED 310 is in use, and the ready light is off or flashes in an alerting color when the AED 310 needs attention.

[034] Below the ready light is an on/off button 320. The on/off button is pressed to turn on the AED 310 for use. To turn off the AED 310 the rescuer 220 holds the on/off

button down for one second or more. An information button 322 flashes when information is available for the rescuer 220. The rescuer 220 depresses the information button to access the available information. A caution light 324 blinks when the AED 310 is acquiring heartbeat information from the patient 210 and lights continuously when a shock is advised, alerting the rescuer 220 and others that no one should be touching the patient 210 during these times. A shock button 326 is depressed to deliver a shock after the AED 310 informs the rescuer 220 that a shock is advised. An infrared port 328 on the side of the AED 310 is used to transfer data between the AED 310 and a computer. This data port finds used after the patient 210 has been rescued and a physician desires to have the AED 310 event data downloaded to his or her computer for detailed analysis. A speaker 313 provides voice instructions to the rescuer 220 to guide the rescuer 220 through the use of the AED 310 to treat the patient 210. A beeper 330 is provided which "chirps" when the AED 310 needs attention such as electrode pad replacement or a new battery. As previously described, the CPR coaching device 100 includes a physiological sensor for sensing a physiological characteristic. Signals representing the physiological information of the sensed physiological characteristic are then provided to the AED 310. Based on the ECG signals acquired by the AED 310 and the physiological information obtained by the CPR coaching device, a treatment protocol can be determined by the AED 310. In another embodiment the CPR coaching device includes ECG electrodes on the body-contacting surface of the device for the sensing of the patient's ECG signal. The ECG signal detected by the CPR coaching device is coupled to the ECG front end circuit 202 for processing. In one implementation the CPR coaching device of this embodiment is applied to the patient's chest before the usual defibrillator electrodes are unwrapped and applied. The ECG sensor on the coaching device can thereby give the defibrillator a "quick look" at the patient's ECG waveform. For instance, if the ECG signals is sensed and processed to determine that the patient exhibits a viable ECG signal, the defibrillator can alert the rescuer that defibrillation is not advised for the patient. The rescuer does not need to unwrap and apply the defibrillation electrodes to

the patient and another form of therapy may be recommended by the defibrillator such as CPR. From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.