Cerebral oxygen extraction across different exercise intensities: Role of arterial PCO2P_CO₂

Stability in cerebral oxygen extraction fraction (OEF) is typically determined by alterations in cerebral blood flow (CBF). At rest, arterial partial pressure of carbon dioxide () and OEF exhibit a strong inverse relationship owing to the powerful influence of on cerebral resistance, CBF and therefore oxygen delivery; however, it is unclear whether this relationship also exists during exercise, especially when supramaximal, during which marked hyperventilation‐induced reductions in induce cerebrovascular vasoconstriction and lower CBF. We determined whether: (1) supramaximal exercise yields the largest change in OEF versus lower intensities, correlated with reductions in ; and (2) declines in (independent of exercise) determine changes in OEF. Blood was sampled from the brachial/radial artery and internal jugular vein during: (1) 60 min, 34% maximal O 2 uptake (SUB; n = six males, six females); (2) 4 min, 90% maximal O 2 uptake (MAX; n = six males, six females); (3) 1−2 min of high‐intensity sprinting, ∼110% maximal O 2 uptake (HIS; n = six males, five females); and (4) resting hyperventilation‐induced hypocapnia (HYPO; n = six males, five females). OEF was calculated as: [ The ΔOEF was greatest during HIS [estimated marginal mean: 15.6% (95% confidence interval: 12.4, 18.8)] and HYPO [17.7% (14.5, 20.9)] compared with SUB [−0.9% (−4.0, 2.1); p < 0.0001 vs. HIS and vs. HYPO] and MAX [2.5% (−0.5, 5.6); p < 0.0001 vs. HIS and vs. HYPO]. Reductions in were greatest in HIS [−12.9 mmHg (−14.6, −11.2)] and HYPO [−9.2 mmHg (−10.9, −7.6)] compared with MAX [−6.2 mmHg (−7.8, −4.6)] and SUB [1.4 mmHg (−0.2, 2.9); all comparisons p < 0.0001]. The ΔOEF was inversely related to both in the pooled analysis [β = −1.65 (−2.23, −1.07); p < 0.0001] and within each of the conditions. In conclusion, probably owing to reductions in CBF, hypocapnia per se increased OEF in a similar manner to supramaximal sprinting, indicating that exercise is non‐obligatory in this process.