Comparative studies of regional CNS blood flow autoregulation and responses to CO2 in the cat. Effects of altering arterial blood pressure and PaCO2 on rCBF of cerebrum, cerebellum, and spinal cord.

Autoregulation and CO2 responses were investigated concurrently in cerebrum, cerebellum, and spinal cord of 19 cats by means of hydrogen clearance. Under ketamine and nitrous oxide anesthesia at normal systemic mean arterial blood pressure (MABP 123 +/- 18.4 mmHg, mean +/- standard deviation) blood flow was 86 +/- 30.0 ml/100 g/min in the cerebrum, 48 +/- 13.6 ml/100 g/min in the cerebellum, and 46 +/- 18.7 ml/100 g/min in the spinal cord. During normocapnia (PaCO2 27-33 mmHg) for every mmHg of PaCO2 variation an average flow change of 1.7 ml/100 g/min was found in the cerebrum, corresponding change rates in the cerebellum and in the spinal cord were 1.1 and 0.9 ml/100 g/min/mmHg, respectively. Thus, the effect of carbon dioxide appears to be positively correlated with the normal level of regional perfusion and metabolism. Flow values within 10% of control were recorded in the cerebrum at MABPs ranging from 79 to 123% of normal blood pressure, 53 to 146% in the cerebellum, and 83 to 128% in the spinal cord. These results suggest greater susceptibility to pressure dependent ischemia of cerebrum and spinal cord, with relative resistance of the cerebellum.