CEREBRAL BLOOD-FLOW IS DETERMINED BY ARTERIAL-PRESSURE AND NOT CARDIOPULMONARY BYPASS FLOW-RATE

Background. During cardiopulmonary bypass, global hypoperfusion of the brain has been shown to result in ischemic insult and subsequent neur ologic injury. Furthermore, outcome after focal cerebral ischemia depe nds on collateral circulation, which is determined by the parameters o f global perfusion. We therefore measured cerebral blood now during in dependent manipulations of arterial blood pressure and pump now rate t o determine which of these hemodynamic parameters regulates cerebral p erfusion during cardiopulmonary bypass. Methods. Seven anesthesized ba boons were placed on cardiopulmonary bypass and fooled to 28 degrees C . Pump now rate and arterial blood pressure were altered in varied seq uence to each of four conditions: (1) full flow (2.23 +/- 0.06 L . min (-1) . m(-2), mean +/- standard deviation) at high pressure (61 +/- 2 mm Hg), (2) full now (2.23 +/- 0.06 L min(-1) . m(-2)) at low pressure (24 +/- 3 mm Hg), (3) low now (0.75 L . min(-1) . m(-2)) at high pres sure (62 +/- 2 mm Hg), and (4) low now (0.75 L min(-1) . m(-2) at low pressure (23 +/- 3 mm Hg). During each of these hemodynamic conditions cerebral blood flow was measured by washout of intracarotid xenon(133 ). Results. Cerebral blood now was greater at high blood pressure than at low pressure during cardiopulmonary bypass both at low now (34 +/- 8.3 versus 14.1 +/- 3.7 mL . min(-1) . 100 g(-1)) and full how (27.6 +/- 9.9 versus 16.8 +/- 3.7 ml min(-1) . 100 g(-1)) (p < 0.01). At com parable mean arterial blood pressures alteration of pump flow rate pro duced no changes in cerebral blood now. Conclusions. These results ind icate that cerebral blood flow during moderately hypothermic cardiopul monary bypass is regulated by arterial blood pressure and not pump flo w rate.