Resting and Exercise Response to Altitude in Patients with Chronic Obstructive Pulmonary Disease

Kelly PT, Swanney MP, Stanton JD, Frampton C, Peters MJ, Beckert LE. Resting and exercise response to altitude in patients with chronic obstructive pulmonary disease. Aviat Space Environ Med 2009; 80:102–7.

Introduction: Exposure to altitude invariably involves some form of physical activity. There are limited data available to help predict the response to activity at altitude in patients with chronic obstructive pulmonary disease (COPD). The aim of the present study was to investigate the response to acute altitude exposure at rest and during exercise in patients with COPD. Methods: Sea level measures of cardio-pulmonary function were compared to the resting and exercise hypoxemic response at the summit of the Mt. Hutt ski field (2086 m), New Zealand, in 18 patients with COPD. Results: Ascent from sea level to altitude caused significant hypoxemia at rest (P_ao₂: 75 ± 9 vs. 51 ± 6 mmHg), and during a walk test (41 ± 7 mmHg). At altitude, the walk test distance was reduced by 52%. Sea level P_ao₂ and S_ao₂ correlated with resting P_ao₂ (r = 0.69) and S_ao₂ (r = 0.79) at altitude. Diffusion capacity corrected for alveolar volume (K_CO) correlated with resting S_ao₂ (r = 0.74) and exercise P_ao₂ (r = 0.75) at altitude. Aerobic capacity correlated with the walk test distance at altitude (r = 0.70). Spirometry, lung volumes, and ventilatory reserve did not correlate with the hypoxemic response to altitude. Discussion: Baseline arterial oxygen levels and K_CO are key measures in predicting the hypoxemic response to acute altitude exposure in patients with COPD. The impairment in gas exchange associated with COPD is a significant mechanism causing altitude-related hypoxemia in this group.