Increased right ventricular compliance in response to continuous positive airway pressure

The right ventricular hemodynamic effects of incremental continuous positive airway pressure (CPAP) were assessed in 16 studies in nine unanesthetized, spontaneously breathing sheep. In seven sheep, studies were performed before and after the induction of sepsis. CPAP was applied in four increments of 4 mm Hg via a cuffed tracheostomy tube. Cardiac output, right ventricular ejection fraction (RVEF) and right ventricular end-diastolic volume (RVEDV) were assessed by thermodilution. In this model, incremental CPAP produced similar effects in septic and nonseptic studies. Cardiac output was preserved by a progressive increase in heart rate (106 +/- 25 to 126 +/- 29, p less than 0.05) in spite of a significant decline in stroke volume index (49 +/- 7 to 43 +/- 7, p less than 0.05). Transmural pulmonary artery pressure and pulmonary vascular resistance index increased with incremental CPAP whereas RVEF declined (0.38 +/- 0.05 to 0.31 +/- 0.05, p less than 0.05). Transmural right atrial pressure declined significantly (7.7 +/- 1.7 to 4.8 +/- 2.9, p less than 0.05) whereas RVEDV was unchanged. In this study incremental CPAP was associated with an enhancement of right ventricular compliance. Further, right ventricular preload was preserved in spite of the measured increase in intrathoracic pressure and cardiac output was maintained in the face of a CPAP-related increase in right ventricular afterload by compensatory increases in heart rate and right ventricular work.