title: Cerebral desaturation during exercise reversed by O2 supplementation.
abstract: 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 +/- 1 mmHg; mean +/- SE) and O2 pressure (77 +/- 2 mmHg) as well as the hemoglobin saturation (91.9 +/- 0.7%) were reduced (P < 0.05). ScO2 was reduced from 80 +/- 2 to 63 +/- 2% (P < 0.05), and the near-infrared spectroscopy-determined concentration changes in deoxy- (DeltaHb) and oxyhemoglobin (DeltaHbO2) of the vastus lateralis muscle increased 22 +/- 3 microM and decreased 14 +/- 3 microM, 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). ScO2 remained close to the resting level during exercise (79 +/- 2 vs. 81 +/- 2%), and although the muscle DeltaHb (18 +/- 2 microM) and DeltaHbO2 (-12 +/- 3 microM) were similar to those established without O2 supplementation, work capacity increased 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.
authors.affiliation: Copenhagen Muscle Research Center, Department of Anesthesia, Rigshospitalet, University of Copenhagen, 2100 Copenhagen O, Denmark. h.bay@dadlnet.dk
authors.forename: H B
authors.initials: HB
authors.lastname: Nielsen
authors.forename: R
authors.initials: R
authors.lastname: Boushel
authors.forename: P
authors.initials: P
authors.lastname: Madsen
authors.forename: N H
authors.initials: NH
authors.lastname: Secher
mesh_terms: D000328:Adult; D001921:Brain / Q000378:metabolism*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D010100:Oxygen / Q000502:physiology*; D010101:Oxygen Consumption
chemical_list: D010100:Oxygen