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 O-2 fraction of 0.21 or 0.30 in a crossover design. During exercise with an inspired O-2 fraction of 0.21, the arterial CO2 pressure (35 +/- 1 mmHg; mean +/- SE) and O-2 pressure (77 +/- 2 mmHg) as well as the hemoglobin saturation (91.9 +/- 0.7%) were reduced (P < 0.05). Scot was reduced from 80 +/- 2 to 63 +/- 2% (P < 0.05), and the near-infrared spectroscopy-determined concentration changes in deoxy- (Delta Hb) and oxyhemoglobin (Delta HbO(2)) of the vastus lateralis muscle increased 22 +/- 3 mu M and decreased 14 +/- 3 mu M, respectively (P < 0.05). Increasing the inspired Oz fraction to 0.30 did not affect ventilation (174 +/- 41/min), but arterial CO2 pressure (37 +/- 2 mmHg), O-2 pressure (165 +/- 5 mmHg), and hemoglobin Oz saturation (99 +/- 0.1%) increased (P < 0.05). Scot remained close to the resting level during exercise (79 +/- 2 vs. 81 +/- 2%), and although the muscle Delta Hb (18 +/- 2 I-IM) and Delta HbO(2) (-12 +/- 3 mu M) were similar to those established without O-2 supplementation, work capacity increased from 389 +/- 11 to 413 +/- 10 W (P < 0.05). These results indicate that an elevated inspiratory O-2 fraction increases exercise performance related to maintained cerebral oxygenation rather than to an effect on the working muscles.