Cerebral blood flow during submaximal and maximal dynamic exercise in humans

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 (V̇O(2max)). 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 (rang 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 < 0.01]. CBF did not differ significantly between work loads from 32 (24-33) to 86% (74-96) of V̇O(2max) (n = 10). During exercise, mean arterial pressure increased from 84 (60-100) to 101 (78-124) Torr (P < 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.