Measuring cerebrovascular reactivity: the dynamic response to a step hypercapnic stimulus

摘要

We define cerebral vascular reactivity (CVR) as the ratio of the change in blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) signal (S) to an increase in blood partial pressure of CO2 (PCO2): % Delta S/Delta PCO2 mm Hg. Our aim was to further characterize CVR into dynamic and static components and then study 46 healthy subjects collated into a reference atlas and 20 patients with unilateral carotid artery stenosis. We applied an abrupt boxcar change in PCO2 and monitored S. We convolved the PCO2 with a set of first-order exponential functions whose time constant tau was increased in 2-second intervals between 2 and 100 seconds. The tau corresponding to the best fit between S and the convolved PCO2 was used to score the speed of response. Additionally, the slope of the regression between S and the convolved PCO2 represents the steady-state CVR (ssCVR). We found that both prolongations of tau and reductions in ssCVR (compared with the reference atlas) were associated with the reductions in CVR on the side of the lesion. tau and ssCVR are respectively the dynamic and static components of measured CVR.