Maximal exercise and muscle oxygen extraction in acclimatizing lowlanders and high altitude natives

• Published in: The Journal of physiology Vol. 573; no. 2; pp. 535 - 547
• Main Authors: Lundby, Carsten, Sander, Mikael, Van Hall, Gerrit, Saltin, Bengt, Calbet, José A. L.
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 01-06-2006; Blackwell Publishing Ltd; Blackwell Science Inc
• Subjects: Acclimatization - physiology; Adult; Altitude; Exercise Test - methods; Humans; Integrative; Male; Muscle, Skeletal - physiology; Oxygen Consumption - physiology; Physical Exertion - physiology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2006.106765

The tight relation between arterial oxygen content and maximum oxygen uptake within a given person at sea level is diminished with altitude acclimatization. An explanation often suggested for this mismatch
is impairment of the muscle O 2 extraction capacity with chronic hypoxia, and is the focus of the present study. We have studied six lowlanders during maximal
exercise at sea level (SL) and with acute (AH) exposure to 4100 m altitude, and again after 2 (W2) and 8 weeks (W8) of altitude
sojourn, where also eight high altitude native (Nat) Aymaras were studied. Fractional arterial muscle O 2 extraction at maximal exercise was 90.0 ± 1.0% in the Danish lowlanders at sea level, and remained close to this value in
all situations. In contrast to this, fractional arterial O 2 extraction was 83.2 ± 2.8% in the high altitude natives, and did not change with the induction of normoxia. The capillary
oxygen conductance of the lower extremity, a measure of oxygen diffusing capacity, was decreased in the Danish lowlanders
after 8 weeks of acclimatization, but was still higher than the value obtained from the high altitude natives. The values
were (in ml min −1 mmHg −1 ) 55.2 ± 3.7 (SL), 48.0 ± 1.7 (W2), 37.8 ± 0.4 (W8) and 27.7 ± 1.5 (Nat). However, when correcting oxygen conductance for
the observed reduction in maximal leg blood flow with acclimatization the effect diminished. When calculating a hypothetical
leg at altitude using either the leg blood flow or the O 2 conductance values obtained at sea level, the former values were almost completely restored to sea level values. This would
suggest that the major determinant for not to increase with acclimatization is the observed reduction in maximal leg blood flow and O 2 conductance.