Middle cerebral artery blood velocity during intense static exercise is dominated by a Valsalva maneuver

Lifting of a heavy weight may lead to "blackout" and occasionally also to cerebral hemorrhage, indicating pronounced consequences for the blood flow through the brain. We hypothesized that especially strenuous respiratory straining (a Valsalva-like maneuver) associated with intense static exercise would lead to a precipitous rise in mean arterial and central venous pressures and, in turn, influence the middle cerebral artery blood velocity (MCA V(mean)) as a noninvasive indicator of changes in cerebral blood flow. In 10 healthy subjects, MCA V(mean) was evaluated in response to maximal static two-legged exercise performed either with a concomitantly performed Valsalva maneuver or with continued ventilation and also during a Valsalva maneuver without associated exercise (n = 6). During static two-legged exercise, the largest rise for mean arterial pressure and MCA V(mean) was established at the onset of exercise performed with a Valsalva-like maneuver (by 42 +/- 5 mmHg and 31 +/- 3% vs. 22 +/- 6 mmHg and 25 +/- 6% with continued ventilation; P < 0.05). Profound reductions in MCA V(mean) were observed both after exercise with continued ventilation (-29 +/- 4% together with a reduction in the arterial CO(2) tension by -5 +/- 1 Torr) and during the maintained Valsalva maneuver (-21 +/- 3% together with an elevation in central venous pressure to 40 +/- 7 mmHg). Responses to performance of the Valsalva maneuver with and without exercise were similar, reflecting the deterministic importance of the Valsalva maneuver for the central and cerebral hemodynamic response to intense static exercise. Continued ventilation during intense static exercise may limit the initial rise in arterial pressure and may in turn reduce the risk of hemorrhage. On the other hand, blackout during and after intense static exercise may reflect a reduction in cerebral blood flow due to expiratory straining and/or hyperventilation.