Robustly Accounting for Vascular Reactivity Differences Across Subjects Using Breath-Hold

Kevin Murphy¹, Ashley D. Harris¹, Richard G. Wise¹

Separating BOLD vascular and metabolic responses is often achieved using hypercapnic challenges. A simple way of elevating blood CO₂ concentrations to measure vascular reactivity is breath-holding. Two aspects of this vascular reactivity measure are often neglected: breath-holds are usually modelled as blocks even though CO₂ accumulates over time and increases in CO₂ differ between subjects, both of which must be considered when using vascular reactivity as a calibration tool. This study determines that the appropriate model for the BOLD breath-hold response is derived from end-tidal CO₂ traces and that individual differences in CO₂ increases must be taken into account.