The relationship of regional cerebrovascular CO2 reactivity to blood pressure and regional resting flow.

The Relationship of Regional Cerebrovascular CO, Reactivity to Blood Pressure and Regional Resting Flow • Cerebrovascular CO 2 reactivity (the change in cerebral blood flow per mm Hg change in Pa c02) is shown to be directly related to resting flow and inversely related to blood pressure for regional as well as for mean CBF data. Both regional and mean CO 2 reactivity therefore are proportional to the ratio resting flow. This ratio is the blood pressure reciprocal of resistance and may be called conductance. When regional CO 2 reactivity for 428 cerebral areas is plotted against an approximation of regional conductance, the data describe positive linear relationships similar to those found when mean CO;, reactivity is plotted against mean conductance. These relationships can be demonstrated whether CO 2 reactivity is calculated with specific or percent change in flow, the data describe positive linear lerationships similar to those found when mean CO 2 basal tone of the cerebrovascular bed. The way in which CO 2 reactivity relates to conductance, therefore, may be a more reliable index of the integrity of the cerebro-vascular CO 2 response than the CBF change per se. Analysis of CO 2 reactivity as a function of conductance may facilitate the interpretation of mean and regional CO 2 reactivity and may provide a more meaningful basis for comparison of the CO 2 response between individuals. Additional Key Words autoregulation cerebral blood flow (CBF) conductance CO 2 response perfusion pressure resistance 133 Xenon • A prior report suggested that the change in mean cerebral blood flow (CBF) in response to a From the Departments of Neurology and Radiology change in Paco 2 is related to blood pressure and to mean resting CBF values. 1 Analysis of 133 Xenon clearance data for 29 patients indicated that mean CO 2 reactivity (the mean change in CBF per millimeter Hg change in Paoo 2) 1S directly related to mean resting CBF and inversely related to mean arterial blood pressure (BP); i.e., mean CO 2 reactivity is proportional to the ratio mean resting CBF mean arterial BP ' This ratio is the reciprocal of cerebrovascular resistance and may be called conductance. The previous report indicated a positive linear correlation between mean hemispheric CO 2 reactiv-725