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NEUROSURGICAL ANESTHESIA

The Continuous Assessment of Cerebrovascular Reactivity: A Validation of the Method in Healthy Volunteers

Wolfson Brain Imaging Centre, Cambridge Medical Research Council’s Centre for Brain Repair and Academic Neurosurgery Unit, Addenbrooke’s Hospital, Cambridge, United Kingdom

Address correspondence and reprint requests to Stefan Piechnik, MScEE, Academic Neurosurgery Unit, PO Box 167, Addenbrooke’s Hospital, Hills Rd., Cambridge CB2 2QQ, UK. Address e-mail to S.K.Piechnik{at}iname.com

Using transcranial Doppler ultrasonography, we investigated the moving correlation between slow waves in arterial blood pressure (ABP) and blood flow velocity (FV) at different levels of cerebrovascular vasodilation provoked by changing PETCO₂. Fourteen healthy volunteers were examined. The FV in middle cerebral arteries, PETCO₂, and ABP were recorded during normocapnia, hypercapnia, and hypocapnia. The moving correlation coefficients between ABP and mean FV (FVm) or systolic FV (FVs) during spontaneous fluctuations in ABP were calculated for 3-min epochs and averaged for each investigation, thus yielding the mean index (Mx) and systolic index (Sx). As a reference method, Aaslid’s cuff tests were performed to obtain the rate of regulation (RoR). RoR, Mx, and Sx significantly depended on PETCO₂ (analysis of variance, P < 0.00001). At high PETCO₂, cerebrovascular reactivity was disturbed as reflected in RoR values of <0.17/s for all volunteers and increased values of Mx (>0.4 in 86% of volunteers) and Sx (>0.2 in 79% of volunteers). Overall, there was a reasonably good correlation of both Mx and Sx with RoR (R² = 0.65 and 0.58, respectively).

Implications: Indices derived from the correlation between spontaneous fluctuations of blood flow velocity wave form and arterial blood pressure may be used for the noninvasive continuous monitoring of cerebrovascular reactivity.

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