Functional Capacity Beyond 350 m in Patients with Chronic Obstructive Pulmonary Disease: A Retrospective Analytical...

The six-minute walk test (6MWT) in chronic obstructive pulmonary disease (COPD) may be interpreted using either an absolute walking-distance threshold or a percentage of the predicted distance, but these approaches are rarely compared within the same cohort. We examined whether absolute and relative 6MWT criteria classify functional impairment differently and whether they show different associations with resting hypoxemia.

We retrospectively analyzed 75 adults with confirmed COPD who were followed at a tertiary pulmonary outpatient clinic between 2012 and 2018. For the historical categorical classification, the absolute criterion was defined as ≤350 m versus >350 m, and the relative criterion as ≤80% versus >80% of predicted distance after percentage-predicted values had been rounded to the nearest whole percentage. Clinical characteristics, modified Medical Research Council dyspnea score, spirometry, arterial blood gases, 6MWT-derived variables, agreement between criteria, age- and sex-adjusted analysis of covariance, and multivariable logistic regression for hypoxemia (PaO₂ < 60 mmHg) were evaluated.

The absolute criterion identified older and more dyspneic patients, whereas the relative criterion identified patients with greater dyspnea, lower FEV₁, lower FVC, and lower PaO₂. Agreement between the criteria was moderate (κ = 0.64; 95% CI 0.48-0.80), and 14 patients who walked >350 m were classified as impaired by the relative criterion. In age- and sex-adjusted logistic regression, both the absolute criterion (OR 2.82; 95% CI 1.02-7.82; p = 0.046) and the relative criterion (OR 4.48; 95% CI 1.54-12.98; p = 0.006) were associated with hypoxemia. In a sensitivity analysis additionally adjusted for FEV₁, the relative criterion remained associated with hypoxemia (OR 3.95; 95% CI 1.32-11.79; p = 0.014).

The absolute and relative 6MWT criteria classified some patients differently and provided partially complementary information. These exploratory findings require prospective validation before either approach is used to guide clinical decision-making.