Autoregulation of cerebral blood flow and its relation to cerebrospinal fluid pH.

Internal carotid artery blood flow (IFBF) was determined in each of nine Macaca mulatta by means of a flow transducer implanted around an internal carotid artery. The monkeys were lightly anesthetized, intubated, and paralyzed. Normoxia and normocarbia were maintained stable throughout the experiment. ICBF was monitored while mean arterial blood pressure (MABP) was lowered by withdrawal of blood. MABP was kept within the known limits of autoregulation in order not to compromise CBF. Cerebrospinal fluid (CSF) from the cisterna magna was analyzed for pH PCO2, and PO2 before and after a 30-min hypotensive period in which MABP was lowered from 116 +/- 4 to 70 +/- 2 mmHg (mean +/- SE). Corresponding HCO3- concentrations were calculated. The decrease in MABP did not result in a significant reduction in ICBF but elicited a 37% reduction in calculated cerebrovascular resistance, indicating normal autoregulation. Mena CSF pH was not significantly decreased (P less than 0.05); it changed from 7.320 +/- 0.010 to 7.317 +/- 0.010 after the induced hypotensive period. Thus CSF pH does not appear to have a significant role in cerebral blood flow autoregulation.