We acknowledge that as a variable for the assessment of cerebrovascular function,total content of CO2 likely only has significance in settings wheresome aspect of blood CO2 transport (i.e., Hb, [H+],[HCO3−], etc.)is altered – e.g., anaemia or otherpathologies, high altitude, exercise, etc. During single CVR tests, calculationof total CO2 content will provide little benefit overPaCO2, however in this study, it provided insight into theunderlying factors allowing for the maintenance of CVR. Here, GSTM1 is linked to anemia (phenotype).