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

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Abstract
Cerebrovascular CO 2 reactivity (the change in cerebral blood flow per mm Hg change in Pa co co 2 ) 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/blood pressure. This ratio is the 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 2 , 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 cerebrovascular 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.