One Year Change in 6-Minute Walk Test Outcomes is Associated with COPD Prognosis

Abstract

Six-minute walk test (6MWT) measures walking distance (6MWD) and desaturation status in chronic obstructive pulmonary disease (COPD) patients. This study aimed to examine whether change in 6MWD and desaturation in 1 year were risk factors for later mortality, lung function decline and number of exacerbations. A total of 295 COPD patients performed 6MWT at baseline and 1 year later in the Bergen COPD cohort study 2006–2011. They were clinically examined and interviewed at annual visits. Mortality information was collected from the Norwegian Cause of Death Registry in 2015. We performed cox regression for mortality outcomes, linear mixed effect models for lung function, and negative binomial regression for exacerbations. Patients who desaturated in both 6MWTs had increased risk of all-cause and respiratory mortality, hazard ratio (HR) 2.7 (95% confidence interval [CI] 1.5–5.0) and 3.6 (95% CI 1.7–7.6), respectively, compared to non-desaturators. Patients who desaturated only at second 6MWT were at risk for all-cause mortality (HR 2.0, 95% CI 1.0–3.8). There were no apparent association between 6MWD and mortality. Desaturation in second 6MWT was associated with later increased rate of decline in forced vital capacity (FVC) % predicted (after 1 year predicted mean 4.2% above non-desaturators, after 5 years 0.7% below). Decline in 6MWD ≥ 30m was borderline (p = 0.06) associated with later decline in forced expiratory volume in 1 second % predicted, and with exacerbations (p = 0.07). Repeated desaturation in the 6MWT over time in COPD patients is a risk factor for all-cause and respiratory mortality, while onset of desaturation is associated with future FVC decline.