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This Article Full Text Full Text (PDF) All Versions of this Article: 586/9/2381    most recent jphysiol.2007.150128v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Vogiatzis, I. Articles by Wagner, P. D. PubMed PubMed Citation Articles by Vogiatzis, I. Articles by Wagner, P. D. Related Collections Skeletal Muscle and Exercise

¹ Department of Critical Care Medicine and Pulmonary Services, Evangelismos Hospital, ‘M. Simou and G.P. Livanos Laboratories’, National and Kapodistrian University of Athens, Athens, Greece
² Department of Physical Education and Sport Sciences, National and Kapodistrian University of Athens, Athens, Greece
³ Department of Exercise Science, Concordia University Montreal, Quebec, Canada
⁴ School of Human Kinetics, University of British Columbia, Vancouver, Canada
⁵ Department of Medicine, University of California, San Diego, La Jolla, CA, USA

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.

(Received 19 December 2007; accepted after revision 10 March 2008; first published online 13 March 2008)
Corresponding author S. Zakynthinos: Medical School of Athens University, Department of Critical Care and Pulmonary Services, Evangelismos Hospital, 45–47 Ipsilandou Str. GR 106 75, Athens, Greece. Email: szakynthinos{at}yahoo.com