Altitude effect on COPD in SPIROMICS cohort

Abstract

Studies suggest higher mortality in COPD patients residing at high altitude. Nevertheless, the impact of altitude on functional capacity and health status in COPD is unknown. Within the SPIROMICS cohort, we compared COPD patients from sea level (Los Angeles & San Francisco, n=400), with those from high-altitude (Salt Lake City & Denver, >1250m altitude, n=310). Multivariable models were used to compare symptoms, exacerbation frequency, functional exercise capacity, percent emphysema, and health status. The high-altitude group was younger with more current smokers, less asthma history, higher supplemental oxygen use, and a history of more acute exacerbations (AE). Adjusted for FEV1, age, sex, race, smoking status, and pack-years, the high-altitude group had more emphysema percentage by CT (+3.2%, CI 2.6-3.7%, p<0.001). High altitude was associated with shorter 6MWD (-67 m, CI -51m to -84m, P=<0.001), for more frequent CAT≥10 (OR 1.69, CI 1.16-2.47, p=0.006) and poorer health status (+4.4 SGRQ, CI +1.8-+7.1, score, p=0.001). Differences in 6MWD were maintained when controlled for supplemental oxygen use. Analyzing longitudinal outcomes adjusted for baseline AE and FEV1, the high-altitude group had more severe AE in the first year of follow up compared to the sea level group (IRR 2.47, CI 1.18-5.16, p=0.016). We found no difference in mortality, FEV1 decline, or progression of HRQoL score by SGRQ between groups. Our results suggest that living with COPD at high altitude is associated with more emphysema and poorer functional capacity and health status in comparison to sea level habitation. Whilst more AE was observed in the first year of follow up, more research is needed to understand the impact of altitude on COPD outcomes.