Cerebrovascular reactivity differences in healthy cerebral gray and white matter

To quantify the speed and magnitude of cerebrovascular reactivity (CVR) metrics in hemispheric gray and white matter.

A standardized isoxic hypercapnic cerebrovascular stimulus was administered using an automated arterial gas targeting system while monitoring blood oxygen-level dependent MRI. The correlation between the blood oxygen-level dependent signal and end-tidal partial pressure of carbon dioxide were measured over time, enabling calculation of CVR metrics including the magnitude and speed (TAU) of the vascular response. The average CVR magnitude and TAU metrics were obtained from 50 healthy participants in the following regions: anterior, middle, and posterior cerebral artery (ACA, MCA, PCA) territory gray matter, the striatum, the thalamus, and hemispheric white matter.

The average MCA CVR is 17.39% greater than ACA CVR (95% confidence interval [CI]: 3.50, 31.28), and the average PCA CVR is 43.03% (95% CI: 29.13, 56.91) and 21.84% (95% CI: 10.00, 33.68) greater than ACA CVR and MCA CVR, respectively. The average TAU in the six regions were ACA = 29.5 ± 9.7 s, MCA = 29.4 ± 8.7 s, PCA = 28.6 ± 10.2 s, striatum = 30.5 ± 8.9 s, thalamus = 25.7 ± 10.0 s, and white matter = 46.3 ± 6.9 s. TAU was similar among all regions investigated except for the white matter, which was approximately 60% slower than the other regions (p < 0.0001).

In healthy individuals, there are significant differences in CVR metrics among the ACA, MCA, PCA gray-matter vascular territories, thalamus, striatum, and hemispheric white matter. Future investigations of CVR should consider the presence of regional variability in CVR metrics when comparing healthy and diseased populations.