Spirometry and Respiratory Muscle Function During Ascent to Higher Altitudes

Abstract

Alterations in lung function at a high altitude (HA) influence exercise capacity, exacerbate hypoxia, and possibly promote predisposition to high-altitude illness. The effects of the HA on lung function and the mechanisms underlying these alterations are currently under investigation. Here, we present a review of the documented alterations in pulmonary physiology and lung functions at the HA in humans. As the first interface between the environment and the body, the lung plays a vital role in the transfer of oxygen from air to blood. The respiratory system adapts to hypoxic stress at rest and during exercise at a HA when oxygen and carbon dioxide flux from tissues is greater. Hypoxic stimuli induce an increase in ventilatory drive and metabolic cost incurred by the respiratory muscles in addition to substantial dyspnea, which may limit exercise tolerance. The exchange of oxygen and carbon dioxide is significantly affected owing to the lower driving pressure for oxygen from air to blood and more rapid transit time of blood across the pulmonary capillaries. Diffusion limitation and ventilation/perfusion mismatch additionally occur, thereby accentuating hypoxemia. Studies on lung and respiratory muscle functions have disclosed a fluctuating course for spirometric measurements, respiratory muscle strength, and endurance at the HA. Specifically, transient increases in these parameters initially occur on ascent to each new altitude, followed by a gradual decline during the longer stay. Despite these restrictions, humans cope remarkably well in times of considerable stress from the hypoxic environment.

Keywords

high altitude, ventilation, exercise, gas exchange, ventilatory drive, dyspnea, respiratory muscle endurance, spirometry