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1Department of Physical Education, University of Las Palmas de Gran Canaria, 35010 Canary Islands, Spain; 2The Copenhagen Muscle Research Centre, Rigshospitalet, 2200 Copenhagen N, Denmark; 3Department of Medicine, Section of Physiology, University of California San Diego, La Jolla, California 92093; and 4Department of Exercise Science, Concordia University, Montreal, Quebec H4B 1R6, Canada
Submitted 2 September 2003 ; accepted in final form 28 April 2004
With altitude acclimatization, blood hemoglobin concentration increases while plasma volume (PV) and maximal cardiac output (
max) decrease. This investigation aimed to determine whether reduction of max at altitude is due to low circulating blood volume (BV). Eight Danish lowlanders (3 females, 5 males: age 24.0 ± 0.6 yr; mean ± SE) performed submaximal and maximal exercise on a cycle ergometer after 9 wk at 5,260 m altitude (Mt. Chacaltaya, Bolivia). This was done first with BV resulting from acclimatization (BV = 5.40 ± 0.39 liters) and again 2–4 days later, 1 h after PV expansion with 1 liter of 6% dextran 70 (BV = 6.32 ± 0.34 liters). PV expansion had no effect on max, maximal O2 consumption (
O2), and exercise capacity. Despite maximal systemic O2 transport being reduced 19% due to hemodilution after PV expansion, whole body O2 was maintained by greater systemic O2 extraction (P < 0.05). Leg blood flow was elevated (P < 0.05) in hypervolemic conditions, which compensated for hemodilution resulting in similar leg O2 delivery and leg O2 during exercise regardless of PV. Pulmonary ventilation, gas exchange, and acid-base balance were essentially unaffected by PV expansion. Sea level max and exercise capacity were restored with hyperoxia at altitude independently of BV. Low BV is not a primary cause for reduction of max at altitude when acclimatized. Furthermore, hemodilution caused by PV expansion at altitude is compensated for by increased systemic O2 extraction with similar peak muscular O2 delivery, such that maximal exercise capacity is unaffected.
hypoxia; exercise; hemodynamics; blood volume; maximal oxygen uptake
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