Agreement and repeatability of vascular reactivity estimates based on a breath-hold task and a resting state scan

Abstract

FMRI BOLD responses to changes in neural activity are influenced by the reactivity of the vasculature. By complementing a task-related BOLD acquisition with a vascular reactivity measure obtained through breath-holding or hypercapnia, this unwanted variance can be statistically reduced in the BOLD responses of interest. Recently, it has been suggested that vascular reactivity can also be estimated using a resting state scan.

This study aimed to compare three breath-hold based analysis approaches (block design, sine–cosine regressor and CO ₂ regressor) and a resting state approach (CO ₂ regressor) to measure vascular reactivity. We tested BOLD variance explained by the model and repeatability of the measures. Fifteen healthy participants underwent a breath-hold task and a resting state scan with end-tidal CO ₂ being recorded during both. Vascular reactivity was defined as CO ₂-related BOLD percent signal change/mm Hg change in CO ₂.

Maps and regional vascular reactivity estimates showed high repeatability when the breath-hold task was used. Repeatability and variance explained by the CO ₂ trace regressor were lower for the resting state data based approach, which resulted in highly variable measures of vascular reactivity.

We conclude that breath-hold based vascular reactivity estimations are more repeatable than resting-based estimates, and that there are limitations with replacing breath-hold scans by resting state scans for vascular reactivity assessment.