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.