Abstract 132: Compliance Changes in the Aorta Following Chest Compressions in a Standard and High Impulse Model

Abstract

Introduction: In cardiopulmonary resuscitation (CPR), chest compressions eject blood from the aorta and into the circulation. Following return of spontaneous circulation (ROSC), the circulation generated by the heart may be hemodynamically compromised, notably in its aortic compliance, or the aorta’s ability to resist blood pressure changes in response to blood volume changes. We investigated the relationship between CPR force delivery and relative change in aortic compliance in standard and high impulse chest compression models. Hypothesis: We hypothesized that average compliance would increase following chest compressions and that high impulse CPR would yield larger compliance changes than compliance changes in standard CPR. Methods: Central aortic pressure (CAP) waveforms were retrospectively analyzed via Millar catheters in female swine separated into standard CPR (n=4) and high impulse CPR (n=5). Ventricular fibrillation was induced and left untreated for 8 minutes, followed by 5 minutes of CPR and drugs. Rescue shocks were then delivered. Compliance was defined as stroke volume divided by the pressure difference between the dicrotic notch and end diastole. Stroke volume was estimated by using a previously validated model, which defined stroke volume as the area beneath the systolic portion of the CAP waveform multiplied by both a calibration constant and a ratio of time in diastole over time in systole. Compliances were calculated from CAP waveforms in ten consecutive beats before and after CPR with custom software built using MATLAB. A 2-way ANOVA was performed on average compliance across ten beats before and after chest compressions in both standard and high impulse CPR. Results: The average compliance (mL/mmHg) at baseline or pre-CPR (203), was significantly different from the average compliance post-CPR (335) (p=.03). The compliance change in standard CPR (151) did not significantly differ from compliance change in high impulse CPR (116) (p=.27). Conclusion: We observed a significant compliance increase in beats post-CPR compared to beats pre-CPR in both standard and high impulse groups. A significant difference in compliance change was not found when comparing standard vs. high impulse CPR.