Regional cerebral blood flow distribution during exercise: Influence of oxygen

We investigated regional changes in cerebral artery velocity during incremental exercise while breathing normoxia (21% O-2), hyperoxia (100% O-2) or hypoxia (16% 02) [n = 10; randomized cross over design]. Middle cerebral and posterior cerebral arterial velocities (MCAv and PCAv) were measured continuously using transcranial Doppler ultrasound. At rest, only PCAv was reduced (-7%; P = 0.016) with hyperoxia. During low-intensity exercise (40% workload maximum [Wmax]) MCAv (+17 cm s(-1); +14 cm s(-1)) and PCAv (+9 cm s(-1); +14 cm s(-1)) were increased above baseline with normoxia and hypoxia, respectively (P < 0.05). The absolute increase from rest in MCAv was greater than the increase in PCAv between 40 and 80% Wmax with normoxia; this greater increase in MCAv was also evident at 60% Wmax with hypoxia and hyperoxia. Hyperoxic exercise resulted in larger absolute (+19 cm s(-1)) and relative (+40%) increases in PCAv compared with normoxia. Our findings highlight the selective changes in PCAv during hyperoxic incremental exercise. (C) 2012 Elsevier B.V. All rights reserved.