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The cerebral metabolic ratio is not affected by oxygen availability during maximal exercise in humans
Author(s) -
Volianitis S.,
FabriciusBjerre A.,
Overgaard A.,
Strømstad M.,
Bjarrum M.,
Carlson C.,
Petersen N. T.,
Rasmussen P.,
Secher N. H.,
Nielsen H. B.
Publication year - 2008
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2007.142273
Subject(s) - rowing , medicine , vo2 max , endocrinology , anaerobic exercise , chemistry , heart rate , blood pressure , physical therapy , history , archaeology
Intense exercise decreases the cerebral metabolic ratio of O 2 to carbohydrates (glucose +½ lactate) and the cerebral lactate uptake depends on its arterial concentration, but whether these variables are influenced by O 2 availability is not known. In six males, maximal ergometer rowing increased the arterial lactate to 21.4 ± 0.8 m m (mean ± s.e.m. ) and arterial–jugular venous (a–v) difference from −0.03 ± 0.01 m m at rest to 2.52 ± 0.03 m m ( P < 0.05). Arterial glucose was raised to 8.5 ± 0.5 m m and its a–v difference increased from 1.03 ± 0.01 to 1.86 ± 0.02 m m ( P < 0.05) in the immediate recovery. During exercise, the cerebral metabolic ratio decreased from 5.67 ± 0.52 at rest to 1.70 ± 0.23 ( P < 0.05) and remained low in the early recovery. Arterial haemoglobin O 2 saturation was 92.5 ± 0.2% during exercise with room air, and it reached 87.6 ± 1.0% and 98.9 ± 0.2% during exercise with an inspired O 2 fraction of 0.17 and 0.30, respectively. Whilst the increase in a–v lactate difference was attenuated by manipulation of cerebral O 2 availability, the cerebral metabolic ratio was not affected significantly. During maximal rowing, the cerebral metabolic ratio reaches the lowest value with no effect by a moderate change in the arterial O 2 content. These findings suggest that intense whole body exercise is associated with marked imbalance in the cerebral metabolic substrate preferences independent of oxygen availability.