CPR COACHING DEVICE PROVIDING TACTILE FEEDBACK

[001] The invention relates generally to cardio-pulmonary resuscitation ("CPR") coaching and training devices, and more particularly, to a device that calculates a depth for a chest compression and provides tactile feedback to a rescuer when the compression depth is sufficient.

[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. 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 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 of delivery of defibrillation shocks to a patient, CPR is administered to promote blood flow.

[003] Studies have suggested that a patient's survival rate increases by a factor of 3 to

4 when high-quality CPR is administered. 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 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, or both 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. For example, as described 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. As previously discussed, conventional CPR coaching devices provide feedback to a rescuer in the form of visual and audible feedback. In some environments, however, visual and audible feedback may be difficult for the rescuer to perceive. For example, in a loud environment, such as a crowded room or on a busy street corner, audible feedback may be drowned out by the ambient background noise. Consequently, the rescuer will not be able to hear the audible coaching prompts. As for visual feedback, the device displaying the visual feedback can be obscured from the rescuer's view, such as when many people are present or the display device is awkwardly located relative to the rescuer. Additionally, in the case of a remote display device, the rescuer may be forced to look in a direction other than at the patient to observe the visual feedback, which can be distracting to the rescuer while trying to focus on administering chest compressions. There are examples of CPR coaching devices that provide visual feedback directly on the body of the device allow a rescuer to focus their vision in the same direction of the patient. However, providing the visual feedback directly on the body of the coaching device forces the rescuer to grasp the CPR coaching device in a manner which avoids covering the visual feedback with the rescuer's hands. A CPR coaching device can be designed to have a portion of the body extend in manner that allows visual feedback to be observed even while the rescuer's hands are placed over

the CPR coaching device. The extended portion, however, can make the CPR coaching device bulkier and more difficult to handle.

[007] Therefore, there is a need for a CPR coaching device that provides an alternative form of coaching feedback to a rescuer other than visual and audible forms of feedback.

[008] One aspect of the invention provides a system for assisting a rescuer administer

CPR to a patient. The system includes a device configured to be placed between the hands of the rescuer and the chest of the patient during administration of chest compressions. The device measures acceleration during a chest compression and calculates a displacement during the chest compression. Based on the calculated displacement, the device provides tactile feedback to the rescuer at a displacement depth to indicate that the depth of the chest compression is sufficient.

[009] Another aspect of the invention provides a CPR coaching device. The device includes a housing and an accelerometer that is configured to measure acceleration of the device and generate an output signal indicative of the measured acceleration. A calculation circuit coupled to the accelerometer calculates a displacement for the CPR coaching device from the measured acceleration and a control circuit coupled to the calculation circuit compares the calculated displacement to a displacement range or threshold and generates an active control signal in response to the calculated displacement meeting and/or exceeding the displacement threshold and/or range. The device further includes an actuator coupled to the control circuit to receive the control signal and fixed in the housing. The actuator is configured to generate a tactile sensation transmitted to the housing in response to the active control signal.

[010] Another aspect of the invention provides a method for coaching a rescuer in administering chest compressions to a patient. The method includes measuring acceleration of a chest compression, calculating a displacement value from the measured acceleration, and providing a tactile indicator to the rescuer that the calculated displacement corresponds to a chest compression of sufficient depth.

[011] In the drawings:

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

[013] FIGURE 2 illustrates a rescuer using a CPR coaching device according to an embodiment of the present invention for administering CPR to a patient.

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

[015] FIGURE 4 is a diagram of a CPR coaching device according to another embodiment of the present invention combining tactile and visual forms of feedback.

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

[017] 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.

[018] FIGURE 1 illustrates a CPR coaching device 100 according to an embodiment of the present invention. Unlike conventional CPR coaching devices, the CPR coaching device 100 provides tactile feedback to a rescuer to coach the administration of CPR to a patient. For example, in the CPR coaching device 100 the tactile feedback is used to indicate to the rescuer when a chest compression is sufficient in depth. In contrast to conventional CPR coaching devices, the CPR coaching device 100 can provide the rescuer with feedback, even in situations where audible and visual feedback is not effective in coaching the rescuer. As will be described in more detail below, tactile feedback can be combined with audible and visual feedback in alternative embodiments of the present invention.

[019] An illustration 110 depicting a patient's torso is included on an upper surface

120 of the CPR coaching device 100 to illustrate the position and orientation of the CPR coaching device 100 when used. As shown in FIGURE 2, with the CPR coaching device 100 positioned on the sternum of a patient 210, a rescuer 220 prepares to apply 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, however, the rescuer's hands are placed on the CPR coaching device 100 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. As will be described in more detail below, when the depth of a compression is sufficient, as measured by the CPR coaching device 100, tactile feedback is provided to the rescuer 220 to indicate that the compression is sufficient and that the compression should be released.

[020] Figure 3 is a simplified block diagram illustrating various components included in the CPR coaching device 100 according to an embodiment of the invention. An accelerometer 302 included in the CPR coaching device 100 detects and measures acceleration of the CPR coaching device 100. The accelerometer 302 is oriented and fixed in the CPR coaching device 100 for providing an output signal ACCOUT that is indicative of acceleration experienced by the accelerometer 302, and consequently, the CPR coaching device 100. During use of the CPR coaching device 100, the CPR coaching device 100 is displaced along an axis of travel when chest compressions are applied by the rescuer 220. The accelerometer 302 is conventional, and can be implemented using known accelerometer devices and circuits currently available.

[021] As known, acceleration along the axis of travel can be resolved into displacement along the axis of travel by doubly integrating the ACCOUT signal produced by the accelerometer 302. A calculation and control unit 304 coupled to the accelerometer 302 receives the ACCOUT signal and performs the double integration operation to calculate the displacement of the CPR coaching device 100. In one embodiment, a processor is included in the calculation and control unit 304 to execute an algorithm to perform the double integration. In another embodiment, an integrator

circuit is included in the calculation and control unit 304 to doubly integrate the ACCOUT signal. Various algorithms and operations known in the art can be used to perform the double integration operation, and consequently, in the interest of brevity, will not be discussed in detail herein. An example of calculating displacement from an acceleration measurement is described in U.S. Patent No. 6,306,107 to Myklebust et al., which is incorporated herein by reference.

[022] The calculation and control unit 304 is further operable to compare the calculated displacement to a displacement threshold that represents the desired depth of chest compressions. Conventional control circuitry can be used in the calculation and control unit 304. In response to the calculated displacement reaching the displacement threshold, the calculation and control unit 304 provides an active control signal CNTRL to an actuator 306. The actuator 306 is coupled to the upper surface 120 of the CPR coaching device 100 to create the tactile feedback that is sensed by a rescuer 220 when the compression being applied to the patient 210 is sufficiently deep.

[023] As previously discussed, the CPR coaching device 100 provides tactile feedback to the rescuer 220 when the depth of the compression is sufficient and the compression should be released for the next compression. Various forms of tactile feedback can be employed. For example, in one embodiment of the present invention the actuator 306 can cause the upper surface 120 of the CPR coaching device 100 to deflect when a chest compression is sufficiently deep. The physical deflection of the upper surface 120 provides a perceptible indication that is felt by the hands of the rescuer 220 when applying a downward force during compression. The sensation of the upper surface 120 deflecting serves as notice that the compression should be released and allow the chest to return to its normal position. The deflection can be tailored to promote tactile sensation, such as the actuator 306 quickly releasing the upper surface 120 inwardly when the depth of the compression is sufficient. Where it is desirable to provide audible feedback in addition to the tactile feedback, the actuator 306 can comprise a snap-dome device with a quick, releasing sensation to provide an audible clicking sound when the compression depth is sufficient. The snap-dome can deflect and produce a

tactile clicking sensation simply in response to the compressive force of the rescuer during CPR or, alternatively, when the required compressive depth has been reached, a solenoid adjacent to the snap-dome can be commanded to strike or deflect the snap- dome to produce the tactile sensation.

[024] In other embodiments of the invention the tactile feedback is provided by deflecting the upper surface 120 of the CPR coaching device 100 outwardly, such as by the actuator 306 providing a gentle poking or lifting sensation of the upper surface 120 that can be felt by the hands of the rescuer 220 when applying the chest compression.

[025] In another embodiment of the present invention, the CPR coaching device 100 utilizes a tapping sensation that is transmitted through the upper surface 120 of the CPR coaching device 100 when the depth of the compression is sufficient. In this embodiment, the actuator 306 is operable to strike the interior surface of the upper surface 120 when the calculation and control unit 304 generates an active CNTRL signal. The tapping is detected through the hands of the rescuer 220 and indicates that the compression should be released so that the patient's chest can return to its normal uncompressed position.

[026] In another embodiment of the invention, the actuator 306 is operable to cause the CPR coaching device 100 to vibrate when the calculated displacement reaches the displacement threshold. This embodiment is an example of a CPR coaching device where the tactile feedback is not provided through the upper surface, but is still effective in indicating to the rescuer 220 that the applied compression is sufficiently deep.

[027] Other forms of tactile feedback not specifically described in the present application can be used as well to indicate to the rescuer 220 that the chest compression is sufficiently deep and should be released. The various forms of tactile feedback can also be combined to provide a CPR coaching device having multiple tactile feedback mechanisms. The various forms of tactile feedback can be implemented using circuits and components of conventional design and operation. Consequently, it will be

appreciated that those ordinarily skilled in the art will be able to practice embodiments of the invention based on the description provided herein.

[028] As previously mentioned, in alternative embodiments of the invention tactile feedback can be combined with other forms of feedback, such as visual feedback. FIGURE 4 illustrates a CPR coaching device 400 that provides both tactile feedback, as previously discussed with reference to CPR coaching device 100, as well as visual feedback. The visual feedback of the CPR coaching device 400 is provided by an array of lights 404, such as light emitting diodes ("LEDs"), and a pacing meter 420. A calculation and control unit included in the CPR coaching device 400 is operable to calculate displacement and generate an active CNTRL signal to trigger the tactile feedback, as previously discussed with reference to the calculation and control unit 304. The calculation and control unit of the CPR coaching device 400 is further operable to analyze the calculated displacement to determine if the rescuer allows for sufficient release of a compression before applying a next chest compression.

[029] Based on the analysis, the processor controls the array of lights 404 to indicate whether the compression is deep enough and whether the release is sufficient. For example, with the CPR coaching device 400 placed on the chest of the patient 210 and no pressure applied, segment 410 is illuminated indicating a fully released position. As the patient's chest is compressed by the rescuer 220, additional segments of the array of lights 404 are sequentially illuminated until segment 414 is illuminated to indicate that the compression is sufficiently deep. As the compression is released, and the patient's chest begins to return to its normal position, the segments sequentially switch off. Thus, if the chest compression is not sufficient, segment 414 is never illuminated, indicating that the chest compression needs to be deeper. Additionally, when the compression is released, and the segments of the array of lights 404 sequentially switch off, if more than segment 410 is illuminated before the next compression begins, the rescuer has failed to sufficiently release the previous compression. The tactile feedback can also be used to coach the proper release between chest compressions. For instance, tactile feedback of one sound or sensation can be delivered when compression reaches

the proper depth or depth range, and another tactile sound or sensation can be delivered when the compression pressure is released as fully as necessary. The device will make a "click" sound and sensation when the proper depth is reached and a "clack" sound and sensation when the compression is released to the proper degree. A further alternative is to deliver a distinct sound or sensation if the chest is too deeply compressed. Thus, the rescuer is coached to deliver a repetitive sequence of "click" and "clack" sensations with each chest compression.

[030] In the embodiment of the invention shown in Figure 4, the processor of the CPR coaching device 400 is further operable to calculate a frequency of the chest compressions applied by the rescuer 220. The calculated frequency is used by the processor to determine if the pace of compressions is adequate. The pacing meter 420 provides visual feedback to the rescuer on the adequacy of the pace of the compressions. A pointer 422 is oriented to point in a direction relative to the pace of the compressions. When the pointer 422 is pointing within a range 424 (as shown in FIGURE 4), the pace of compressions is satisfactory. However, if the pointer 422 is pointed outside of the range 424, the pace of compressions should be increased or decreased, depending on which side of the range 424 the pointer 422 is pointing.

[031] Although tactile feedback is combined with visual feedback in the CPR coaching device 400, other forms of feedback, such as audible feedback, can be combined with tactile feedback in alternative embodiments.

[032] The previous embodiments of CPR coaching devices were described as being separate devices that coach a rescuer in administering CPR. FIGURE 5 illustrates a CPR coaching device 500 coupled through cable 502 to a defibrillator 310. The defibrillator 310 represents an automatic external defibrillator ("AED"). Other types of defibrillators such a manually controlled 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 and also protects the layperson user from shocks. Attached to the case 312 by electrical leads are a pair of electrode pads. The electrode pads are in a cartridge 306 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 316 which allows removal of a plastic cover over the electrode pads. The user interface is on the right side of the AED 310. A small ready light 318 informs the user of the readiness of the AED. In this embodiment the ready light blinks after the AED has been properly set up and is ready for use. The ready light is on constantly when the AED is in use, and the ready light is off or flashes in an alerting color when the AED needs attention.

[033] Below the ready light is an on/off button 320. The on/off button is pressed to turn on the AED for use. To turn off the AED a user holds the on/off button down for one second or more. An information button 322 flashes when information is available for the user. The user depresses the information button to access the available information. A caution light 324 blinks when the AED is acquiring heartbeat information from the patient and lights continuously when a shock is advised, alerting the rescuer and others that no one should be touching the patient during these times. Interaction with the patient while the heart signal is being acquired can introduce unwanted artifacts into the detected ECG signal. A shock button 326 is depressed to deliver a shock after the AED informs the rescuer that a shock is advised. An infrared port 328 on the side of the AED is used to transfer data between the AED and a computer. This data port finds used after a patient has been rescued and a physician desires to have the AED event data downloaded to his or her computer for detailed analysis. A speaker 313 provides voice instructions to a rescuer to guide the rescuer through the use of the AED to treat a patient. A beeper 330 is provided which "chirps" when the AED needs attention such as electrode pad replacement or a new battery.

[034] Information measured and calculated by the CPR coaching device 500 can be used by the AED 310. For example, prior to delivering a shock to the patient, the AED 310 can monitor whether administration of CPR has ceased based on information provided to it by the CPR coaching device 500. Another example is providing information regarding the depth and frequency of compressions measured by the CPR coaching device for filtering signal disturbances from an ECG signal taken by the AED 310. Chest compressions typically cause signal disturbances in the ECG signal which

prevent the AED 310 from analyzing the ECG during administration of CPR. By filtering the effect of the chest compressions, the ECG may be analyzed while CPR is administered. In alternative embodiments of the invention, the AED 310 can utilize the information measured and calculated by the CPR coaching device 500 for other purposes such as evaluating the quality of CPR, and consequently, the specific example described herein are not intended to limit the scope of the invention. If the quality of CPR is estimated to be poor, for example, the AED may implement a modified coaching technique or the length of the CPR delivery interval may be extended or shortened, for instance. 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. For example, tactile feedback has been described herein as indicating sufficient compression depth. However, in alternative embodiments, tactile feedback is used to indicate other aspects of administering CPR, such as providing tactile feedback to the rescuer to indicate sufficient release of a compression. Accordingly, the invention is not limited except as by the appended claims.