Variation of Proposed Correlation Indices of Cerebrovascular Reactivity with Change of Arteriolar Diameter

Summary

The purpose of this study was to examine the relationship between proposed correlation indices of cerebrovascular reserve and corresponding changes of cerebrovascular reserve as measured by changes of pial arteriolar diameter. Mild and severe physiologic challenge was produced in piglets by appropriate ventilation with foreign gas mixture and altered alveolar ventilation. Intracranial pressure (ICP), arterial blood pressure (ABP), and video micrometer recordings of pial arteriolar diameter were made. Serial values of ICP and ABP were used to compute the Correlation Coefficient index (Corrx) and the Pressure Reactivity Index (PrX). For the 10 mild physiologic challenge experiments, correlations between percent change index (%ΔCorrx and %ΔPrX) and percent change of pial arteriolar diameter (%Δdia.) induced by mild challenges (n = 40) were 0.51 (p <.005) and 0.097 (p n.s.) respectively. For 8 asphyxia experiments, serial values with respect to time of the correlation indices were correlated with %Δdia. obtained before, during induction and recovery. The grand mean (n = 8) correlation values (± S.D.) of the Corrx and PrX were 0.76 (±0.18, p <.025) and 0.21 (±0.38, p n.s.) respectively. In contrast to the PrX index, changes of the Corrx index significantly correlated with changes of pial arteriolar diameter. However, Corrx and PrX were simultaneously high only during a state of maximum dilation. These findings suggest that sudden salient increases of the Corrx and PrX indices induced by physiologic challenge are indicative of vigorous dilatory response of the cerebral arterioles and loss of cerebrovascular reserve.