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

Area of Science:

• Neuroimaging
• Vascular Neurology
• Physiology

Background:

• Cerebral vascular reactivity (CVR) assesses brain blood flow regulation.
• CVR is typically measured using blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI).
• Characterizing CVR into dynamic and static components can provide a more nuanced understanding of cerebrovascular health.

Purpose of the Study:

• To differentiate dynamic and static components of CVR.
• To investigate CVR in healthy subjects and patients with unilateral carotid artery stenosis.
• To correlate dynamic and static CVR measures with cerebrovascular disease.

Main Methods:

• Defined CVR as the ratio of BOLD signal change to partial pressure of CO2 change (% Δ S/Δ PCO2).
• Applied an abrupt CO2 challenge and modeled the BOLD signal response using exponential functions to determine the time constant (τ) for dynamic CVR.
• Calculated steady-state CVR (ssCVR) from the regression slope between BOLD signal and CO2 levels.

Main Results:

• Prolongation of the time constant (τ) and reduction in steady-state CVR (ssCVR) were observed in patients with unilateral carotid artery stenosis compared to a healthy reference atlas.
• These reductions in dynamic and static CVR components were associated with the side of the cerebrovascular lesion.
• τ represents the dynamic component, and ssCVR represents the static component of measured CVR.

Conclusions:

• CVR can be effectively decomposed into dynamic (τ) and static (ssCVR) parameters.
• Impaired dynamic and static CVR are associated with unilateral carotid artery stenosis.
• These findings highlight the utility of dynamic and static CVR assessment in evaluating cerebrovascular health and disease.