Effects of pulsatile assistance and nonpulsatile flow on subendocardial perfusion during cardiopulmonary bypass.

We compared the effects of pulsatile and nonpulsatile perfusion in 12 dogs on extracorporeal circulation. In beating empty and fibrillating hearts at 37 degrees and 28 degrees C, coronary blood flow was measured by flowmeter and microspheres at diastolic pressures ranging between 50 and 130 mm Hg. At fixed systemic flow rates (range, 600 to 2,400 ml/min), pulsatile perfusion produced a transient (3 to 4 second) augmentation of diastolic pressure and then resulted in the following: (1) decreased peripheral vascular resistance (p less than 0.05); (2) unchanged peak diastolic pressure (compared with nonpulsatile perfusion); (3) decreased mean aortic pressure (6 to 37%) (p less than 0.05); (4) decreased coronary blood flow (10 to 45%) (p less than 0.05); and (5) decreased subendocardial blood flow (from 512 to 438 ml/100 gm/min) (p less than 0.05). Pulsatile perfusion in beating hearts (37 degrees or 28 degrees C) did not reduce subendocardial vascular resistance, but did improve subendocardial perfusion by 27% and 36% in fibrillating hearts at 37 degrees and 28 degrees C, respectively. We conclude that with the exception of ventricular fibrillation, pulsatile assistance offers no advantage over nonpulsatile perfusion and has the potential disadvantage of requiring higher pump flow rates to achieve any desired level of coronary and subendocardial flow.