Emphysema-predominant copd had a greater 5-year mortality and a worse annual decline in lung function than airway obstruction-predominant copd or asthma at initial same degree of airflow obstruction

Background and Objectives: We studied whether the extent of exertional oxygen desatura-tion and emphysema could cause greater mortality in COPD and asthma independent of airflow obstruction. Materials and Methods: We performed a 5-year longitudinal observational study in COPD and asthma patients who matched for airflow obstruction severity. All subjects performed a 6-min walk test (6MWT) and high-resolution computed tomography (HRCT) and followed spirometry and oxygen saturation (SpO₂ ) during the 6MWT every 3–6 months. Overall survival was recorded. Cumulative survival curves were performed according to the Kaplan–Meier method and compared with the log-rank test. Results: The COPD group had higher emphysema scores, higher ∆inspiratory capacities (ICs) and lower SpO₂ during the 6MWT, which showed a greater yearly decline in FEV₁ (40.6 mL) and forced vital capacity (FVC) (28 mL) than the asthma group (FEV₁, 9.6 mL; FVC, 1.2 mL; p < 0.05). The emphysema-predominant COPD group had an accelerated annual decline in lung function and worse survival. The nadir SpO₂ ≤ 80% and a higher emphysema score were the strong risk factors for mortality in COPD patients. Conclusions: The greater structural changes with a higher emphysema score and greater desaturation during the 6MWT in COPD may contribute to worse yearly decline in FEV₁ and higher five-year mortality than in asthma patients with a similar airflow obstruction. The lowest SpO₂ ≤ 80% during the 6MWT and emphysema-predominant COPD were the strong independent factors for mortality in chronic obstructive airway disease patients.