Abstract 288: Chest Wall Stiffness Varies During Cardiopulmonary Resuscitation

Introduction : Displacement of the sternum during cardiopulmonary resuscitation (CPR) is affected by the elastic properties of the chest wall but the dynamic properties of the chest wall have not been described. This study tested whether chest wall stiffness varies with depth of compression, and whether chest wall stiffness changes with repeated compressions. Methods : Acceleration and force applied to the chest wall during CPR were measured using an accelerometer and a force meter “puck” placed between the rescuer hand and the patient sternum (Philips MRX). Displacement of the sternum (double integrated acceleration) was used to calculate chest wall stiffness (force/displacement) using MATLAB and STATA. Changes in stiffness with compression depth and with compression number were analyzed using linear regression. Results : CPR data from 10 subjects with out-of-hospital cardiac arrest provided about 50 measurements per compression and 100-4739 compressions per subject. Chest wall stiffness decreased as depth of compression increased (p<0.001), requiring varying force for any given displacement. Chest wall stiffness at a given depth (25 mm) decreased over consecutive compressions (p<0.001) (Figure 1). Conclusions : Stiffness of the chest wall changes as the depth of compression increases. Over multiple compressions, the stiffness of the chest wall declines, perhaps reflecting loss of rib integrity. Future work should explore whether stiffness is related to optimal chest compression depth.