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Effects of High Altitude Hypoxia on Lung and Chest Wall Function during Exercise

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Final rept. 30 Jun 1988-29 Sep 1991

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We have more precisely than has been done before, defined the mechanical limits of the lung and chest wall for the ventilatory requirements of exercise in healthy persons. In most instances in the normal or moderately fit individual the ventilatory requirement is such that mechanical limitations are barely reached upon expiration, the inspiratory muscles achieve only 40-60 of their capacity for pressure generation and fatigue of the respiratory muscle is not a factor - at least during short term maximum exercise. The greater the macimal VO2, the greater the ventilatory cost and the closer one comes to mechanical limitation of ventilation. Under these conditions, oxygen cost of breathing can approach 13-15 of the total VO2 and during long term exercise the diaphragm becomes fatigued. If hypoxia accompanies the exercise, the ventilatory requirement would increase substantially, diaphragm fatigue occurs earlier, mechanical limitations to expiratory flow and inspiratory pressure development occur at lower work-rates and the diaphragm becomes fatigued in a much shorter exercise time. These factors may contribute significantly to the limitation of exercise performance-especially endurance exercise.

Subject Categories:

  • Anatomy and Physiology
  • Medicine and Medical Research
  • Stress Physiology

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