AHEART September 46/

Nielsen, H. B., R. Boushel, P. Madsen, and N. H. Secher. Cerebral desaturation during exercise reversed by O2 supplementation. Am. J. Physiol. 277 (Heart Circ. Physiol. 46): H1045–H1052, 1999.—The combined effects of hyperventilation and arterial desaturation on cerebral oxygenation (ScO2) 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 6 1 mmHg; mean 6 SE) and O2 pressure (77 6 2 mmHg) as well as the hemoglobin saturation (91.9 6 0.7%) were reduced (P , 0.05). ScO2 was reduced from 80 6 2 to 63 6 2% (P , 0.05), and the near-infrared spectroscopy-determined concentration changes in deoxy(DHb) and oxyhemoglobin (DHbO2) of the vastus lateralis muscle increased 22 6 3 μM and decreased 14 6 3 μM, respectively (P , 0.05). Increasing the inspired O2 fraction to 0.30 did not affect ventilation (174 6 4 l/min), but arterial CO2 pressure (37 6 2 mmHg), O2 pressure (165 6 5 mmHg), and hemoglobin O2 saturation (99 6 0.1%) increased (P , 0.05). ScO2 remained close to the resting level during exercise (79 6 2 vs. 81 6 2%), and although the muscle DHb (18 6 2 μM) and DHbO2 (212 6 3 μM) were similar to those established without O2 supplementation, work capacity increased from 389 6 11 to 413 6 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.