The Relationship of Regional Cerebrovascular CO 2 Reactivity to Blood Pressure and Regional Resting Flow

Cerebrovascular CO2 reactivity (the change in cerebral blood flow per mm Hg change in Paco2) 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 CO2 reactivity therefore are proportional to the ratio resting flow/blood pressure. This ratio is the reciprocal of resistance and may be called conductance. When regional CO2 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 CO2, reactivity is plotted against mean conductance. These relationships can be demonstrated whether CO2 reactivity is calculated with specific or percent change in flow, the data describe positive linear lerationships similar to those found when mean CO2 basal tone of the cerebrovascular bed. The way in which CO2 reactivity relates to conductance, therefore, may be a more reliable index of the integrity of the cerebrovascular CO2 response than the CBF change per se. Analysis of CO2 reactivity as a function of conductance may facilitate the interpretation of mean and regional CO2 reactivity and may provide a more meaningful basis for comparison of the CO2 response between individuals.