Abstract
Background and Objectives: We studied whether the extent of exertional oxygen desaturation 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 Δinspiratory 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.
Highlights
Chronic obstructive pulmonary disease (COPD) and asthma are two of the most common chronic obstructive airway diseases and are characterized by inflammatory airway disease and airflow limitation [1], but with differences in immunology and physiology [1,2]
We have shown that dynamic hyperinflation in COPD decreased the levels of exhaled nitric oxide after the 6-minute walk test (6MWT), while the changes in exhaled NO in asthma after the 6MWT were highly associated with the severity of small airway obstruction; this may differentiate the underlying airway obstruction of asthma or COPD patients, which may be a factor for distinctive patterns of airway inflammation and structural changes from the two diseases [20]
Airflow obstruction was similar between COPD and asthma, the nadir oxygen saturation by pulse oximetry (SpO2) after the 6MWT was significantly lower in the COPD patients at level of forced expiratory volume in 1 s (FEV1) < 35% of the predicted value (Table 1)
Summary
Chronic obstructive pulmonary disease (COPD) and asthma are two of the most common chronic obstructive airway diseases and are characterized by inflammatory airway disease and airflow limitation [1], but with differences in immunology and physiology [1,2]. The presence of emphysema and airway disease, as assessed using computed tomography and decreased pulmonary function, were high-risk factors associated with death in COPD patients [16]. The aim of the study was to evaluate whether the desaturation during the 6MWT and COPD with predominant emphysema would be a risk factor for mortality in COPD and chronic asthma patients at initial similar airflow obstruction and age match. 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
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