Abstract Body: Introduction: In CPR, duty cycle (DC) is the fraction of time dedicated to chest compression or constriction within each chest compression/relaxation cycle. Traditionally, 50% has been the standard DC for CPR. Data from human case series and animal models indicate that the optimal DC may be 30% for sternal piston-based CPR. Unlike sternal CPR, circumferential constriction thoracoabdominal CPR (CCTA-CPR) may function via a thoracic pump mechanism. CCTA-CPR may have enhanced hemodynamics and safety. However, its optimal DC is unknown.
Hypothesis: The optimal DC for CCTA-CPR may also be less than the traditional 50% DC.
Methods: Ventricular fibrillation was induced in female Yorkshire swine (n = 6, 30 kg). CPR was provided by a prototype pneumatic CCTA-CPR machine. DC was varied in 45 second epochs between 30% and 50% at constriction rates of 60, 80, 100 and 120 per minute. The variation in rate was intended for an unrelated study. Aortic (Ao) and right atrial (RA) pressures were measured using micromanometer catheters. Coronary perfusion pressure (CPP) was derived as the difference between the Ao and RA pressures. The change in CPP (Delta-CPP) from the beginning to the end of each treatment epoch was used as the principal indicator of hemodynamics. Results from among all experiments were grouped by treatment type and subjected to Analysis of Variance.
Results: There were no significant differences in absolute Ao or RA. However, absolute and delta CPPs trended higher with 50% DC, and delta-CPP was higher in 5 of 6 pigs.
Conclusion: In contrast to sternal piston CPR, a DC of 50% trended toward being associated with improved indicators of hemodynamics compared to 30% in CTA-CPR. This may reflect the possibility that CTA-CPR leaves the thoracic recoil venous return mechanism intact, while sternal piston CPR generally damages it. With an intact venous return mechanism, the compression phase of cardiac output may be more important.