Abstract 13048: A Simple Model to Describe the Relationship Between Compression Force and Depth During CPR

Abstract

Aim: The relationship between force and depth during manual chest compressions depends on the patient and on the dynamics with which the rescuer applies the force. Force-depth models with many fitting parameters have been proposed making physical interpretation complicated. The aim of this work was to design a simpler force-depth model, accommodating anticipated differences in compression and recoil phases. Materials and Methods: Force and acceleration signals were extracted from out-of-hospital-cardiac arrest (OHCA) defibrillator recordings (TVF&R, OR, USA), equipped with CPR technology. Compression depth and velocity signals were computed from acceleration. We analyzed intervals of 20-s within the 1st min of chest compressions. Our model decomposes the applied force as the sum of an elastic and a damped term, considering different damping coefficients for the compression and recoil phases. Coefficient of elasticity was calculated at the instant of maximum compression depth (null velocity) and damping coefficients at the instants of maximum compression and recoil velocities. The estimated depth signal is shown in the figure. The goodness of the model was assessed through the determination coefficient R 2 . Results: We analyzed 1,074 compressions from 30 OHCA recordings. Median (IQR) compression depth was 4.6 (4.0-5.4) cm; compression rate was 107 (102–113) cpm; coefficient of elasticity was 100.67 (78.95–125.01) N/cm; compression damping coefficient was 2.57 (1.84–3.29) N/(cm/s) and recoil damping coefficient was 3.59 (2.58–4.90) N/(cm/s). Median R 2 was 0.993 (0.984–0.996). Conclusions: This model, derived using fewer parameters, could help with the interpretation of the mechanical properties of the chest during CPR. It may also be useful for the assessment of inter-patient differences with age, sex, and body constitution, as well as of the evolution of elasticity and damping of patient’s chest during the course of resuscitation.