Experimental study of cerebral autoregulation during cardiopulmonary bypass with or without pulsatile perfusion

Twenty-four adult mongrel dogs were divided into four equal groups according to the following method of cardiopulmonary bypass: normothermic continuous (so-called nonpulsatile) perfusion, normothermic pulsatile perfusion, hypothermic continuous perfusion, and hypothermic pulsatile perfusion. Cerebral blood flow was determined by measuring the volume of sagittal sinus venous blood outflow with a transit-time ultrasonic flowmeter. Cardiopulmonary bypass was initiated at a flow rate of 80 ml/kg per minute. Cerebral temperature was maintained at 37 degrees C in the normothermic groups and at 25 degrees C in the hypothermic groups. Arterial pH and carbon dioxide were maintained within the physiologic range by alpha-stat acid-base regulation. Mean cerebral perfusion pressure and blood flow were not affected during 90 minutes of the bypass. The respective values were 67.1 mm Hg and 37.1 ml/100 gm brain per minute with normothermic continuous perfusion, 72.8 mm Hg and 39.0 ml/100 gm per minute with nonpulsatile perfusion, 98.0 mm Hg and 23.0 ml/gm per minute with hypothermic continuous perfusion, and 86.8 mm Hg and 22.3 ml/100 gm per minute with hypothermic pulsatile perfusion. Pump flow rates were altered from 10 to 120 ml/kg per minute in a stepwise fashion to obtain graded changes of perfusion pressure. Cerebral blood flow, however, was not changed significantly by cerebral perfusion pressure so long as perfusion pressure was greater than 50 mm Hg. Conversely, cerebral blood flow changed proportionally with cerebral perfusion pressure at a pressure less than 50 mm Hg. The correlation between cerebral blood flow and perfusion pressure was described as two separate lines determined by linear regression. The slope of the regression line relating cerebral blood flow to perfusion pressure was 0.16 +/- 0.08 for a cerebral perfusion pressure above 50 mm Hg and 0.68 +/- 0.11 below 50 mm Hg in the normothermic continuous perfusion group; 0.14 +/- 0.09 and 0.32 +/- 0.09 with normothermic pulsatile perfusion; 0.10 +/- 0.04 and 0.62 +/- 0.18 with hypothermic continuous perfusion; 0.09 +/- 0.08 and 0.39 +/- 0.04 in the hypothermic pulsatile perfusion group. The slope above 50 mm Hg was significantly smaller and closer to zero in all groups than it was at a perfusion pressure below 50 mm Hg (p < 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)