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Related Experiment Videos

Limiting factors for exercise at extreme altitudes.

J B West1

  • 1Department of Medicine, University of California, San Diego, La Jolla 92093-0623.

Clinical Physiology (Oxford, England)
|May 1, 1990
PubMed
Summary

High altitude survival relies on increased ventilation, but oxygen delivery to muscles remains limited. Even at rest, arterial oxygen levels are critically low on Mt Everest.

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Area of Science:

  • Human Physiology
  • High-Altitude Medicine
  • Exercise Physiology

Background:

  • Human survival at high altitudes necessitates significant physiological adaptations to combat severe oxygen deprivation.
  • Increased ventilation is crucial for maintaining alveolar oxygen partial pressure (PO2) against reduced inspired PO2.

Purpose of the Study:

  • To investigate the physiological responses and limitations of human performance at extreme altitudes, specifically Mt Everest.
  • To understand the mechanisms behind reduced aerobic capacity and altered metabolic responses during high-altitude exercise.

Main Methods:

  • Physiological measurements of ventilation, arterial PO2, cardiac output, and oxygen uptake at extreme altitudes.
  • Assessment of myocardial contractility and oxygen delivery to exercising muscles.
  • Analysis of blood lactate and bicarbonate levels during exercise at high altitude.

Main Results:

  • Arterial PO2 is severely reduced at rest and decreases further with exercise due to lung diffusion limitation.
  • Despite hyperventilation, cardiac output is maintained, but stroke volume is reduced.
  • Oxygen delivery to muscles is diffusion-limited, leading to a maximal oxygen uptake of 20-25% of sea-level values.
  • Anaerobic metabolism is curtailed, with no significant rise in blood lactate predicted above 7500m, possibly due to bicarbonate depletion.

Conclusions:

  • Human physiological function, particularly oxygen transport and utilization, is severely compromised at extreme altitudes like Mt Everest.
  • The myocardium maintains function despite severe hypoxia, but oxygen delivery to exercising muscles becomes a critical limiting factor.
  • Altered metabolic responses, including suppressed lactate production, suggest unique adaptations or limitations in energy metabolism at extreme altitudes.

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