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

Abstract

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.

BOLD‐based cerebrovascular reactivity vascular transfer function isolates amplitude and timing responses to better characterize cerebral small vessel disease

“…Timing information is not new in CVR research. Previous approaches investigating explicit CVR temporal features are limited by underlying assumptions of the BOLD response to hypercapnia, such as generating analytically defined CO 2 input regressors, a convolution of P ET CO 2 , and a ‘haemodynamic response function’, which restricts the residue function to a monoexponential decay response, or a data‐driven approach to fit BOLD time‐series data to a Gaussian model . Others have demonstrated temporal and amplitude shifts in BOLD response to visual stimulation, which, although they robustly demonstrate effects of cerebrovascular disorders such as cerebral angiopathy on CVR, remain limited to the study of the occipital lobe rather than global tissue measures .…”

The BOLD cerebrovascular reactivity response to progressive hypercapnia in young and elderly

“…Analysis of CVR dynamics using methods as described in Poublanc et al, 2015), as well as reference atlas based approaches extended to include baseline hemodynamic information could shed further light on age-related CVR changes. Furthermore, data acquisition at high field strength would provide increased CNR allowing a higher sensitivity to small changes in BOLD-CVR, particularly in the WM.…”

Iterative analysis of cerebrovascular reactivity dynamic response by temporal decomposition

“…(2015) and Poublanc, Crawley, et al. (2015), determined the dynamic vascular response velocity by convolving a controlled PetCO 2 stimulus trace, with either the Hemodynamic Response Function (HRF) or a mono‐exponential dispersion function. Their dynamic vascular response velocity maps (termed Tau and Phase) are fairly similar to our DTP map with clear distinctions between short vascular responses in the gray matter and increasingly prolonged dynamic vascular responses from subcortical to deep white matter.…”

“…(2014) and Poublanc, Crawley, Sobczyk, Montandon, et al. (2015), have previously defined the approach to generate CVR reference atlases, with increased sensitivity for impaired CVR. We have created our reference atlas in a similar fashion.…”