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This Article Full Text Full Text (PDF) All Versions of this Article: 581/1/299    most recent jphysiol.2006.126136v1 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 Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Vogiatzis, I. Articles by Zakynthinos, S. Search for Related Content PubMed PubMed Citation Articles by Vogiatzis, I. Articles by Zakynthinos, S. Related Collections Skeletal Muscle and Exercise

¹ Department of Critical Care Medicine and Pulmonary Services, Evangelismos Hospital, ‘M. Simou and G. P. Livanos Laboratories’
² Department of Physical Education and Sport Sciences, National & Kapodistrian University of Athens, Greece
³ Department of Medicine, University of California, San Diego, CA, USA

Previous work suggests that exercise-induced arterial hypoxaemia (EIAH), causing only moderate arterial oxygen desaturation (: 92 ± 1%), does not exaggerate diaphragmatic fatigue exhibited by highly trained endurance athletes. Since changes in arterial O₂ tension have a significant effect on the rate of development of locomotor muscle fatigue during strenuous exercise, the present study investigated whether hypoxia superimposed on EIAH exacerbates the exercise-induced diaphragmatic fatigue in these athletes. Eight trained cyclists (: 67.0 ± 2.6 ml kg^–1 min^–1; mean ± S.E.M.) completed in balanced order four 5 min exercise tests leading to different levels of end-exercise (64 ± 2, 83 ± 1, 91 ± 1 and 96 ± 1%) via variations in inspired O₂ fraction (: 0.13, 0.17, 0.21 and 0.26, respectively). Measurements were made at corresponding intensities (65 ± 3, 80 ± 3, 85 ± 3 and 90 ± 3% of normoxic maximal work rate, respectively) in order to produce the same tidal volume, breathing frequency and respiratory muscle load at each . The mean pressure time product of the diaphragm did not differ across the four exercise tests and ranged between 312 ± 28 and 382 ± 22 cmH₂O s min^–1. Ten minutes into recovery, twitch transdiaphragmatic pressure (P_di,tw) determined by bilateral phrenic nerve stimulation, was significantly (P = 0.0001) reduced after all tests. After both hypoxic tests (: 0.13, 0.17) the degree of fall in P_di,tw (by 26.9 ± 2.7 and 27.4 ± 2.6%, respectively) was significantly greater (P < 0.05) than after the normoxic test (by 20.1 ± 3.4%). The greater amount of diaphragmatic fatigue in hypoxia at lower leg work rates (presumably requiring smaller leg blood flow compared with normoxia at higher leg work rates), suggests that when ventilatory muscle load is similar between normoxia and hypoxia, hypoxia exaggerates diaphragmatic fatigue in spite of potentially greater respiratory muscle blood flow availability.

(Received 19 December 2006; accepted after revision 18 February 2007; first published online 22 February 2007)
Corresponding author I. Vogiatzis: Thorax Foundation, 3 Ploutarhou Str. 106 75, Athens, Greece. Email: gianvog{at}phed.uoa.gr

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