The Effect of Chronic Altitude Exposure on Chronic Obstructive Pulmonary Disease Outcomes in the SPIROMICS Cohort: An Observational Cohort Study
Rajat Suri, Daniela Markovic, Han Woo, Mehrdad Arjomandi, R. Graham Barr, Russell P. Bowler, Gerard J. Criner, Jeffrey L. Curtis, Mark T. Dransfield, Michael Drummond, Spyridon Fortis, MeiLan K. Han, Eric A. Hoffman, Robert J. Kaner, Joel D. Kaufman, Jerry A. Krishnan, Fernando J. Martínez, Jill Ohar, Victor E. Ortega, Robert Paine, Xavier Soler, Prescott G. Woodruff, Nadia N. Hansel, Christopher B. Cooper, Donald P. Tashkin, Russell G. Buhr, Igor Barjaktarević
Abstract
Abstract Rationale Individuals with chronic obstructive pulmonary disease (COPD) have airflow obstruction and maldistribution of ventilation. For those living at high altitude, any gas exchange abnormality is compounded by reduced partial pressures of inspired oxygen. Objectives Does residence at higher altitude exposure affect COPD outcomes, including lung function, imaging characteristics, symptoms, health status, functional exercise capacity, exacerbations, and mortality? Methods From the SPIROMICS (Subpopulation and Intermediate Outcome Measures in COPD Study) cohort, we identified individuals with COPD living below 1,000 ft (305 m) elevation (n = 1,367) versus above 4,000 ft (1,219 m) elevation (n = 288). Multivariable regression models were used to evaluate associations of exposure to high altitude with COPD-related outcomes. Measurements and Main Results Living at higher altitude was associated with reduced functional exercise capacity as defined by 6-minute-walk distance (−32.3 m [95% confidence interval, −49.8 to −14.8 m]). There were no differences in patient-reported outcomes as defined by symptoms (COPD Assessment Test and modified Medical Research Council dyspnea scale), or health status (St. George’s Respiratory Questionnaire). Higher altitude was not associated with a different rate of FEV1 decline. Higher altitude was associated with lower odds of severe exacerbations (incidence rate ratio, 0.65 [95% confidence interval, 0.46 to 0.90]). There were no differences in small airway disease, air trapping, or emphysema. In longitudinal analyses, higher altitude was associated with increased mortality (hazard ratio, 1.25 [95% confidence interval, 1.0 to 1.55]); however, this association was no longer significant when accounting for air pollution. Conclusions Long-term altitude exposure is associated with reduced functional exercise capacity in individuals with COPD, but this did not translate into differences in symptoms or health status. In addition, long-term high-altitude exposure did not affect progression of disease as defined by longitudinal changes in spirometry. Clinical trial registered with www.clinicaltrials.gov (NCT 01969344).