Cerebrovascular Reactivity in the Brain White Matter: Magnitude, Temporal Characteristics, and Age Effects

Abstract

White matter (WM) comprises about half of the brain and its dysfunction is implicated in many brain disorders. While structural properties in healthy and diseased WM have been extensively studied, relatively little is known about the physiology underlying these structural characteristics. Recent advances in magnetic resonance (MR) technologies provided new opportunities to better understand perfusion and microvasculature in the WM. Here, we aim to evaluate vasodilatory capacity of the WM vasculature, which is thought to be important in tissue ischemia and autoregulation. Fifteen younger and fifteen older subjects performed a CO 2 inhalation task while blood-oxygenation-level-dependent (BOLD) magnetic resonance imaging (MRI) images were continuously collected. The cerebrovascular reactivity (CVR) index showed that the value of CVR in the WM (0.03±0.002%/mm Hg) was positive, but was significantly lower than that in the gray matter (GM) (0.22 ± 0.01%/mm Hg). More strikingly, the WM response showed a temporal delay of 19 ± 3 seconds compared with GM, which was attributed to the longer time it takes for extravascular CO 2 to change. With age, WM CVR response becomes greater and faster, which is opposite to the changes seen in the GM. These data suggest that characteristics of WM CVR are different from that of GM and caution should be used when interpreting pathologic WM CVR results.

Comparing cerebrovascular reactivity measured using BOLD and cerebral blood flow MRI: The effect of basal vascular tension on vasodilatory and vasoconstrictive reactivity

“…However, we did not use the frequency spectrum-based technique for response delay estimation, as low-frequency physiological noise interfered within the frequency bandwidth of our stimulus. Rather, our delay-estimation method is similar to that of Thomas et al (2014). Nonetheless, our findings of earlier response in the frontal lobe and later response in the occipital lobe as well as the subcortical gray matter structures are in agreement with previous findings (Blockley et al, 2011;Bright et al, 2009).…”

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

“…4C), and that of others (Reich and Rusinek, 1989). It may also help explain or interpret elevated WM BOLD-CVR (Thomas et al, 2014) and CBF (Lu et al, 2011) with increasing age that have been reported elsewhere.…”

Magnetic resonance imaging for assessment of cerebrovascular reactivity in cerebral small vessel disease: A systematic review

“…Age, blood pressure and gender are in themselves thought to alter CVR 17,21 and therefore may have affected the results. Even where these variables were reported, the studies varied as to whether they corrected for these factors when assessing CVR.…”

“…There is known to be a significant delay between change in EtCO 2 and change in BOLD signal in the white matter compared to the grey matter. 21,28 It is therefore vital that the different delay between brain structures is taken into account during analysis and that the period of hypercapnia is long enough for all tissues to achieve a representative change in BOLD signal. The delay itself may be an important part of the assessment of CVR.…”