Mechanism and pattern of human cerebrovascular regulation after rapid changes in blood CO2 tension.

Little is known of the mechanism and pattern of cerebrovascular regulation after relatively rapid repeated alterations in blood CO2 tension as might occur in various environmental or disease states. Quantitative measurements of change in the cere-bral circulation have largely been limited to pro-longed steady state conditions because the most accepted technique for measuring cerebral blood flow (CBF) and metabolism requires long periods for equilibration, i.e., the nitrous oxide method of Kety and Schmidt (1). Recently, certain radio-isotope techniques capable of repetitive determina-tions at 1-minute intervals have been utilized in studies of CBF in the control state (2) and in re-sponse to a single alteration in blood CO9 tension in a small number of studies (3). Analysis of the assumptions-upon which these techniques are based and reasons for questioning their adequacy in following rapid changes in flow have recently been detailed by Zierler (4). The purpose of these studies was to measure, by means of an appropriate technique, the pattern of change in CBF during a series of alterations in blood CO2 tension to obtain information con-cerning the mechanism of control of the cerebral circulation during such interventions. The data demonstrate the existence of hysteresis between arterial CO2 tension and CBF during stepwise elevations and depressions of this tension above * Submitted for publication August 4, 1965; accepted