Monitoring mechanical impedance of the thorax with compression and decompression cardiopulmonary resuscitation device

Abstract

To reduce the complications of cardiopulmonary resuscitation (CPR) and increase its effectiveness, the quality of CPR must be measured and feedback provided to the CPR practitioner. Although CPR ancillary devices that attach sensors to measure the compression frequency and depth have been used, these devices did not previously capture the parameters necessary to determine whether the compression position was appropriate, or whether the thorax was deformed by fracture or other causes. In this study, we proposed a system for measuring the mechanical impedance of a patient’s thorax using a load cell and an accelerometer, incorporated into a CPR ancillary device; the mechanical impedance measurements enabled monitoring of the characteristics and deformations of the thorax during in vitro experiments using dummies, and in an animal experiment using two pigs. When CPR was performed, sensors attached to the CPR assist device measured the compression force and movement, and then the single frequency elements of force and velocity at chest compression frequency were calculated. The mechanical impedance can be determined by calculating the ratio of the obtained force to the velocity. Dummies with different elastic moduli show differences in mechanical impedance. In the animal experiment using pigs, the mechanical impedance of the pig’s thorax steadily decreased in response to successive chest compressions. The mechanical impedance system proposed in this study may be useful in the development of new methods to rapidly measure the mechanical properties of the human body or other complex structures.