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1 Department of Physical Education, University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Canary Islands, Spain; The Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen, Denmark
2 The Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen, Denmark
3 The Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen, Denmark; Department of Exercise Science, Concordia University, Montreal, Quebec, Canada
4 Department of Medicine, Section of Physiology, University of California San Diego, La Jolla, California, USA
* To whom correspondence should be addressed. E-mail: lopezcalbet{at}terra.es.
With altitude acclimatization, blood hemoglobin concentration ([Hb]) increases while plasma volume (PV) and maximal cardiac output (Qmax) are lowered. The aim of this investigation was to determine if the reduction of Qmax at altitude is due to a low circulating blood volume (BV). Eight Danish lowlanders (3 females and 5 males age: 24.0±0.6 years (mean ± S.E.M.)) performed submaximal and maximal exercise on a cycle ergometer after 9 weeks at an altitude of 5260m (Mt. Chacaltaya, Bolivia). This was done first with the BV resulting from the acclimatization (BV=5.40±0.39 L) and again two-four days later, one hour after PV expansion with 1 liter of 6% dextran 70 (BV=6.32±0.34 L). PV expansion had no effect on Qmax, maximal VO2 and exercise capacity. Despite maximal systemic O2 transport being reduced 19% due to hemodilution after PV expansion, whole body VO2 was maintained by greater systemic O2 extraction (P < 0.05). Leg blood flow was elevated (P < 0.05) in the hypervolemic conditions which compensated for the hemodilution resulting in similar leg O2 delivery and leg VO2 during exercise regardless of plasma volume. Pulmonary ventilation, gas exchange and acid-base balance were essentially unaffected by PV expansion. Sea level Qmax and exercise capacity were restored with hyperoxia at altitude independently of BV. A low BV is not a primary cause for the reduction of Qmax at altitude when acclimatized. Furthermore, the hemodilution caused by PV expansion at altitude is compensated for by an increased systemic O2 extraction with similar peak muscular O2 delivery, such that maximal exercise capacity is unaffected..
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