Arterial P<scp>co</scp>₂ and cerebral hemodynamics

The effect of arterial Pco 2 in the control of cerebral hemodynamics over the full range of responsiveness of the cerebral vasculature was studied in the rhesus monkey. Cerebral perfusion pressure and arterial O 2 saturation were controlled so that they produced no significant effect on the cerebral circulation. Other possible sources of error, e.g., blood temperature, effect of anesthesia, development of metabolic acidosis, and validity of internal jugular measurements of cerebral blood flow were evaluated. Arterial Pco 2 was varied from 5 to 418 mm Hg in eight animals. The minimum and maximum cerebral blood flows obtained were 18 and 140 ml/min 100 g, respectively. These values were approached when the arterial Pco 2 was in the range of 10–15 mm Hg and 150 mm Hg, respectively. At these levels of arterial Pco 2 the maximum and minimum cerebrovascular resistance occurred. These values were 4.78 and 0.63 mm Hg/ml/min per 100 g, respectively. A mathematical analysis of the data enabled equations relating arterial Pco 2 to cerebrovascular resistance and to cerebral blood flow to be derived. Values predicted by these equations compare favorably with the actual measured data and with similar data in the literature.