Effect of hypobaric hypoxia on blood gases in patients with restrictive lung disease

Several publications have reported effects of hypobaric conditions in patients with chronic obstructive pulmonary disease. To the current authors' knowledge, similar studies concerning patients with restrictive lung disease have not been published. The effect of simulated air travel in a hypobaric chamber on arterial blood gases, blood pressure, and cardiac frequency during rest and 20 W exercise, and the response to supplementary oxygen in 17 patients with chronic restrictive ventilatory impairment has been investigated. Resting oxygen tension in arterial blood (Pa,O2) decreased from 10.4+/-1.6 kPa at sea level to 6.5+/-1.1 kPa at 2,438 m simulated altitude, and decreased further during light exercise in all patients (5.1+/-0.9 kPa). Pa,O2 at this altitude correlated positively with sea-level Pa,O2 and transfer factor of the lung for carbon monoxide (TL,CO), and negatively with carbon dioxide tension in arterial blood (Pa,CO2). Pa,O2 increased to acceptable levels with an O2 supply of 2 L x min(-1) at rest and 4 L x min(-1) during 20 W exercise. In conclusion, most of the patients with restrictive ventilatory impairment developed hypoxaemia below the recommended levels of in-flight oxygen tension in arterial blood during simulated air travel. Light exercise aggravated the hypoxaemia. Acceptable levels of oxygen tension in arterial blood, with only a minor increase in carbon dioxide tension in arterial blood, were obtained by supplementary oxygen.