Association of chest compression and recoil velocities with depth and rate in manual cardiopulmonary resuscitation

Aim: Maximum velocity during chest recoil has been proposed as a metric for chest compression quality during cardiopulmonary resuscitation (CPR). This study investigated the relationship of the maximum velocities during compression and recoil phases with compression depth and rate in manual CPR. Methods: We measured compression instances in out-of-hospital cardiac arrest recordings using custom Matlab programs. Each compression cycle was characterized by depth and rate, maximum compression and recoil velocities (CV and RV), and compression and recoil durations (total and effective). Mean compression and recoil velocities were computed as depth divided by compression and recoil durations, respectively. We correlated CV and RV with their corresponding mean velocities (total and effective), characterized by Pearson's correlation coefficient. Results: CV/RV were strongly correlated with their corresponding mean velocities, with a median r of 0.83 (0.77–0.88)/0.82 (0.76–0.87) in per patient analysis, 0.86/0.88 for all the population. Correlation with mean effective velocities had a median r of 0.91 (0.87–0.94)/0.92 (0.89–0.94) in per-patient, 0.92/0.94 globally (p < 0.001). Total and effective compression and recoil durations were inversely proportional to compression rate. We observed similar RV values among compressions regardless of whether they were compliant with recommended depth and rate. Conversely, we observed different RV values among compressions having the same depth and rate, but presenting very distinct compression waveforms. Conclusion: CV and RV were highly correlated with compression depth and compression and recoil times, respectively. Better understanding of the relationship between novel and current quality metrics could help with the interpretation of CPR quality studies.