Document Detail

The contribution of intrapulmonary shunts to the alveolar-to-arterial oxygen difference during exercise is very small.
MedLine Citation:
PMID:  18339692     Owner:  NLM     Status:  MEDLINE    
Exercise is well known to cause arterial PO2 to fall and the alveolar-arterial PO2 difference(Aa PO2 ) to increase. Until recently, the physiological basis for this was considered to be mostly ventilation/perfusion ((.)VA/(.)Q) 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 PO2 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, FIO2 , 0.13), normoxia (FIO2 , 0.21) and hyperoxia (FIO2 , 1.0) undertaken in balanced order on the same day in seven fit cyclists ((.)VO2max, 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 ((.)VA/(.)Q) 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 PO2 and hypoxaemia during heavy exercise.
Ioannis Vogiatzis; Spyros Zakynthinos; Robert Boushel; Dimitris Athanasopoulos; Jordan A Guenette; Harrieth Wagner; Charis Roussos; Peter D Wagner
Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't     Date:  2008-03-13
Journal Detail:
Title:  The Journal of physiology     Volume:  586     ISSN:  1469-7793     ISO Abbreviation:  J. Physiol. (Lond.)     Publication Date:  2008 May 
Date Detail:
Created Date:  2008-05-02     Completed Date:  2008-06-04     Revised Date:  2013-06-05    
Medline Journal Info:
Nlm Unique ID:  0266262     Medline TA:  J Physiol     Country:  England    
Other Details:
Languages:  eng     Pagination:  2381-91     Citation Subset:  IM    
Medical School of Athens University, Department of Critical Care and Pulmonary Services, Evangelismos Hospital, Athens, Greece.
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MeSH Terms
Oxygen / metabolism*
Physical Endurance / physiology*
Physical Exertion / physiology*
Pulmonary Alveoli / physiology*
Pulmonary Artery / physiology*
Pulmonary Gas Exchange / physiology*
Grant Support
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