Measuring Cerebrovascular Reactivity: The Dynamic Response to a Step Hypercapnic Stimulus

• Published in: Journal of cerebral blood flow and metabolism Vol. 35; no. 11; pp. 1746 - 1756
• Main Authors: Poublanc, Julien, Crawley, Adrian P, Sobczyk, Olivia, Montandon, Gaspard, Sam, Kevin, Mandell, Daniel M, Dufort, Paul, Venkatraghavan, Lashmikumar, Duffin, James, Mikulis, David J, Fisher, Joseph A
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 01.11.2015; Sage Publications Ltd; Nature Publishing Group
• Subjects: Adult; Aged; Aged, 80 and over; Algorithms; Brain Mapping; Carbon Dioxide - blood; Carotid Stenosis - blood; Carotid Stenosis - physiopathology; Cerebrovascular Circulation; Cerebrovascular Disorders - blood; Cerebrovascular Disorders - physiopathology; Female; Functional Laterality; Humans; Hypercapnia - physiopathology; Magnetic Resonance Imaging; Male; Middle Aged; Original; Oxygen - blood; carbon dioxide; hypercapnia; cerebrovascular reactivity; dynamic response; time constant; humans; BOLD signal
• ISSN: 0271-678X; 1559-7016; 1559-7016
• DOI: 10.1038/jcbfm.2015.114

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): % Δ S/Δ 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 τ was increased in 2-second intervals between 2 and 100 seconds. The τ 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 τ and reductions in ssCVR (compared with the reference atlas) were associated with the reductions in CVR on the side of the lesion. τ and ssCVR are respectively the dynamic and static components of measured CVR.