Abstract 82: Chest Stiffness and Force-Depth Relations Change Over Time During Prolonged CPR: An Animal Model

Abstract

INTRODUCTION Chest deformation during CPR results in increased intrathoracic pressure and blood flow. A parameter linked to both deformation and internal pressures is reaction force. However, little is known about the time dependence of the force-depth relationship. In this study we assessed the hypothesis that chest stiffness and force-depth relations change during CPR in a pig model. MATERIAL AND METHODS Fourteen Yorkshire pigs with an average AP diameter of 20 cm were anesthetized after which ventricular fibrillation (VF) was induced. CPR was administered for 21 minutes at compression depths of 5 cm at frequencies of 80-120cpm during which absolute depth and force were measured continuously. The force-depth signal was divided into elastic and viscous components. Corrections were made for incomplete recoil. Chest stiffness was defined as the maximum force for each compression divided by its corresponding depth. Curvature and stiffness over time were studied. RESULTS The force versus depth relation shows that at the start of CPR the relationship is almost linear. As compressions continue, the curve becomes more curved. Chest stiffness starts at relatively high values of 118 +/- 28 N/cm which decreased to 96 +/- 19 N/cm of the original values after 250 compressions. After this point in time only minor changes in stiffness and nonlinearity were observed. CONCLUSION In conclusion, chest stiffness decreases and the force depth relation changes from linear to convex during CPR. Changes take mostly in the initial phase, where after they approach steady state. This is relevant for obtaining adequate blood flow during CPR.