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Copyright ©ERS Journals Ltd 2001
Diaphragm fatigue during exercise at high altitude: the role of hypoxia and workload
1 Dept of Physiology, University of Iceland, Reykjavik, Iceland. 2 Division of Pulmonary Disease, Salvatore Maugeri Foundation, IRCCS, Rehabilitation Institute of Veruno, Italy. 3 Intensive Care Unit, Edoardo Agnelli Hospital, Italy
CORRESPONDENCE: L. Appendini, Fondazione Salvatore Maugeri, Clinica del Lavoro e della Riabilitazione, IRCCS, Instituto di Riabilitazione di Veruno, Divisione di Pneumologia, Via per Revislate 13, I-28010, Veruno, Italy. Fax: 39 0322830294
Keywords: diaphragm fatigue, exercise testing, hypoxia, respiratory mechanics, respiratory muscles
Received: March 27, 2000
Accepted November 23, 2000
The effect of high altitude (HA) on exercise-induced diaphragm fatigue in normal subjects was examined.
Eight normal subjects completed an incremental exercise test at sea level (SL) and at 3,325 m. Before (baseline), during, and after exercise (recovery), maximal transdiaphragm pressure (Pdi,sniff), breathing pattern, and diaphragmatic effort (PTPdi) were measured. Arterialized blood lactate was measured at baseline and during recovery.
At maximal exercise (WRmax) Pdi,sniff fell to 72% and 61% of baseline at SL and HA respectively, recovering to baseline in 60 min at SL, and >60 min at HA. At the 5th min of recovery, circulating lactate was six-fold and seven-fold baseline at SL and HA, respectively. The time course of circulating lactate recovery was as for Pdi,sniff. At WRmax PTPdi was 80.74±9.87 kPa·s–1 at SL and 64.13±8.21 kPa·s–1 at HA. HA WRmax compared to isowork rate, SL data showed a lower Pdi,sniff (8.90±0.68 versus 11.24±0.59 kPa) and higher minute ventilation (117±11 versus 91±13 L·min–1), PTPdi being equal.
To conclude, in normal subjects hypoxia-related effects, and not an increase in diaphragm work, hastens exercise-induced diaphragm fatigue and delays its recovery at high altitude compared to sea level.
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