Cerebral desaturation during exercise reversed by O₂ supplementation

The combined effects of hyperventilation and arterial desaturation on cerebral oxygenation (SC(O₂)) were determined using near-infrared spectroscopy. Eleven competitive oarsmen were evaluated during a 6-min maximal ergometer row. The study was randomized in a double-blind fashion with an inspired O₂ fraction of 0.21 or 0.30 in a crossover design. During exercise with an inspired O₂ fraction of 0.21, the arterial CO₂ pressure (35 ± 1 mmHg; 1 mean ± SE) and O₂ pressure (77 ± 2 mmHg) as well as the hemoglobin saturation (91.9 ± 0.7%) were reduced (P < 0.05). SC(O₂) was reduced from 80 ± 2 to 63 ± 2% (P < 0.05), and the near-infrared spectroscopy-determined concentration changes in deoxy- (ΔHb) and oxyhemoglobin (ΔHbo₂) of the vastus lateralis muscle increased 22 ± 3 μM and decreased 14 ± 3 μM, respectively (P < 0.05). Increasing the inspired O₂ fraction to 0.30 did not affect ventilation (174 ± 4 l/min), but arterial CO₂ pressure (37 ± 2 mmHg), O₂ pressure (165 ± 5 mmHg), and hemoglobin O₂ saturation (99 ± 0.1%) increased (P < 0.05). SC(O₂) remained close to the resting level during exercise (79 ± 2 vs. 81 ± 2%), and although the muscle ΔHb (18 ± 2 μM) and ΔHbO₂ (-12 ± 3 μM) were similar to those established without O₂ supplementation, work capacity in creased from 389 ± 11 to 413 ± 10 W (P < 0.05). These results indicate that an elevated inspiratory O₂ fraction increases exercise performance related to maintained cerebral oxygenation rather than to an effect on the working muscles.