Cerebral blood flow (CBF) in humans was measured at rest and during dynamic exercise on a cycle ergometer corresponding to 56% (range 27–85) of maximal O2 uptake (VO2max). Exercise bouts were performed by 16 male and female subjects, lasted 15 min each, and were carried out in a semisupine position. CBF (133Xe clearance) was expressed as the initial slope index (ISI) and as the first compartment flow (F1). CBF at rest [ISI, 58 (range 45–73); F1, 76 (range 55–98) ml.100 g-1.min-1] increased during exercise [ISI to 79 (57–94) and F1 to 118 (75–164) ml.100 g-1.min-1, P less than 0.01]. CBF did not differ significantly between work loads from 32 (24–33) to 86% (74–96) of VO2max (n = 10). During exercise, mean arterial pressure increased from 84 (60–100) to 101 (78–124) Torr (P less than 0.01) and PCO2 remained unchanged [5.1 (4.6–5.6) vs. 5.4 (4.4–6.3) kPa, n = 6]. These results demonstrate a median increase of 31% (0–87) in CBF by ISI and a median increase of 58% (0–133) in CBF by F1 during dynamic exercise in humans.
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