Method of determining depth of chest compressions during CPR

#The methods and devices described below relate to the field of cardio-pulmonary resuscitation (CPR).

#The American Heart Association guidelines for the correct application of cardio-pulmonary resuscitation (CPR) specify that chest compressions be performed at the rate of 80 to 100 per minute and at a depth, relative to the spine, of 1.5 to 2.0 inches. (Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care, 102 Circulation Supp. I (2000).) However, CPR is physically and emotionally challenging, even for trained professionals. Research has shown that manual chest compressions rarely meet the guidelines. See, for example, Ochoa et al., The Effect of Rescuer Fatigue on the Quality of Chest Compressions, Resuscitation, vol. 37, p. 149–52. See also Hightower et al., Decay in Quality of Closed-Chest Compressions over Time, Ann Emerg Med, 26(3):300–333, Sept. 1995. One of the difficulties of performing correct chest compressions is that the rescuer imprecisely judges the timing and depth of compressions, particularly when the rescuer becomes tired. Thus, if accurate and timely user feedback could be provided to the rescuer then the rescuer would be more likely to perform CPR correctly.

#Various devices have been proposed to assist a rescuer in properly applying CPR. For example, Kelley, Apparatus for Assisting in the Application of Cardiopulmonary Resuscitation, U.S. Pat. No. 5,496,257 (Mar. 5, 1996) shows a device that uses a pressure sensor to monitor compression forces and timing. Groenke et al., AED with Force Sensor, U.S. Pat. No. 6,125,299 (Sep. 26, 2000) shows a device that uses a force sensor to measure the compression force applied to a patient's chest. However, these devices only measure the force applied to the chest and do not measure the actual depth of compressions. A given force can compress the chests of different patients by different amounts, so measuring only force will not provide sufficient or consistent feedback to the rescuer. In addition, force-based measurements may also be inaccurate because of intra-patient variation in thoracic morphology and compliance (stiffness).

#FIG. 1 shows a patient and an accelerometer-based compression monitor in place on a patient.

#FIG. 2 shows a graph of compression depth over time before signal processing, where compression depth is derived from a measured acceleration.

#FIG. 3 shows a graph of compression velocity over time before signal processing, where compression velocity is derived from a measured acceleration.

#FIG. 1 shows a patient 1 and an accelerometer-based compression monitor 2 in place on the patient. An accelerometer-based compression monitor uses one or more accelerometers to determine the depth of compressions. An example of an accelerometer-based compression monitor may be found in our own patent, Halperin et al., CPR Chest Compression Monitor, U.S. Pat. No. 6,390,996 (May 21, 2002), which is hereby incorporated by reference in its entirety. The compression monitor 2 is placed on the sternum 3 of the patient 1, on the rescuer's hands or arms, or on an automatic CPR device. The chest is then compressed. The accelerometer measures the acceleration of compressions and a processor 4 estimates the actual displacement of the accelerometer based on the measured acceleration. The signal processing techniques described below ensure that the estimated actual displacement is accurate and precise.

#The estimated actual displacement may be provided to a displacement display 5 that provides intelligible feedback to a manual CPR provider or to an automated CPR device. Likewise, other CPR-related parameters may be provided to one or more compression device displays 6 (or other means for user feedback). CPR-related parameters include the depth of chest compressions, the velocity of chest compressions, the acceleration of chest compressions, and the patient's ECG.

#In the case of the patient's ECG, the compression monitor may be provided with one or more electrodes. The processor may process the patient's ECG during compressions to produce an estimated actual ECG. The estimated actual ECG may then be provided to an ECG display 7 (or other means for user feedback) that provides intelligible feedback to the manual CPR provider, to an automated CPR device, or to other individuals or devices that monitor the patient's ECG.