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- Title
The contribution of intrapulmonary shunts to the alveolar-to-arterial oxygen difference during exercise is very small.
- Authors
Vogiatzis, Ioannis; Zakynthinos, Spyros; Boushel, Robert; Athanasopoulos, Dimitris; Guenette, Jordan A.; Wagner, Harrieth; Roussos, Charis; Wagner, Peter D.
- Abstract
Exercise is well known to cause arterial to fall and the alveolar–arterial difference (Aa ) to increase. Until recently, the physiological basis for this was considered to be mostly ventilation/perfusion / inequality and alveolar–capillary diffusion limitation. Recently, arterio-venous shunting through dilated pulmonary blood vessels has been proposed to explain a significant part of the Aa during exercise. To test this hypothesis we determined venous admixture during 5 min of near-maximal, constant-load, exercise in hypoxia (in inspired O2 fraction, , 0.13), normoxia ( , 0.21) and hyperoxia ( , 1.0) undertaken in balanced order on the same day in seven fit cyclists ( , 61.3 ± 2.4 ml kg−1 min−1; mean ±s.e.m.). Venous admixture reflects three causes of hypoxaemia combined: true shunt, diffusion limitation and / inequality. In hypoxia, venous admixture was 22.8 ± 2.5% of the cardiac output; in normoxia it was 3.5 ± 0.5%; in hyperoxia it was 0.5 ± 0.2%. Since only true shunt accounts for venous admixture while breathing 100% O2, the present study suggests that shunt accounts for only a very small portion of the observed venous admixture, Aa and hypoxaemia during heavy exercise.
- Publication
Journal of Physiology, 2008, Vol 586, Issue 9, p2381
- ISSN
0022-3751
- Publication type
Article
- DOI
10.1113/jphysiol.2007.150128