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Contribution of respiratory muscle blood flow to exercise-induced diaphragmatic fatigue in trained cyclists
We investigated whether the greater degree of exercise-induced diaphragmatic fatigue previously reported in highly trained athletes in hypoxia (compared with normoxia) could have a contribution from limited respiratory muscle blood flow. Seven trained cyclists completed three constant load 5 min exe...
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Published in: | The Journal of physiology 2008-11, Vol.586 (22), p.5575-5587 |
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Main Authors: | , , , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | We investigated whether the greater degree of exercise-induced diaphragmatic fatigue previously reported in highly trained
athletes in hypoxia (compared with normoxia) could have a contribution from limited respiratory muscle blood flow. Seven trained
cyclists completed three constant load 5 min exercise tests at inspired O 2 fractions ( ) of 0.13, 0.21 and 1.00 in balanced order. Work rates were selected to produce the same tidal volume, breathing frequency
and respiratory muscle load at each (63 ± 1, 78 ± 1 and 87 ± 1% of normoxic maximal work rate, respectively). Intercostals and quadriceps muscle blood flow (IMBF
and QMBF, respectively) were measured by near-infrared spectroscopy over the left 7th intercostal space and the left vastus
lateralis muscle, respectively, using indocyanine green dye. The mean pressure time product of the diaphragm and the work
of breathing did not differ across the three exercise tests. After hypoxic exercise, twitch transdiaphragmatic pressure fell
by 33.3 ± 4.8%, significantly ( P < 0.05) more than after both normoxic (25.6 ± 3.5% reduction) and hyperoxic (26.6 ± 3.3% reduction) exercise, confirming
greater fatigue in hypoxia. Despite lower leg power output in hypoxia, neither cardiac output nor QMBF (27.6 ± 1.2 l min â1 and 100.4 ± 8.7 ml (100 ml) â1 min â1 , respectively) were significantly different compared with normoxia (28.4 ± 1.9 l min â1 and 94.4 ± 5.2 ml (100 ml) â1 min â1 , respectively) and hyperoxia (27.8 ± 1.6 l min â1 and 95.1 ± 7.8 ml (100 ml) â1 min â1 , respectively). Neither IMBF was different across hypoxia, normoxia and hyperoxia (53.6 ± 8.5, 49.9 ± 5.9 and 52.9 ± 5.9
ml (100 ml) â1 min â1 , respectively). We conclude that when respiratory muscle energy requirement is not different between normoxia and hypoxia,
diaphragmatic fatigue is greater in hypoxia as intercostal muscle blood flow is not increased (compared with normoxia) to
compensate for the reduction in , thus further compromising O 2 supply to the respiratory muscles. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2008.162768 |