Inspiratory capacity predicts mortality in patients with chronic obstructive pulmonary disease.

Background: Chronic obstructive pulmonary disease (COPD) severity is usually graded upon the FEV1 reduction and FEV1 has been considered the most important mortality predictor with age in COPD. Recent studies suggest other factors as more powerfully related to mortality than FEV1 in COPD patients. Aim: To assess the impact of inspiratory capacity (IC) on mortality and morbidity in COPD patients during a 5-year follow-up period. Methods: We recruited 222 patients with mild-to-moderate COPD from January 1995 to December 2001 with an average follow-up period of 60 months (range 30–114 months). Among different respiratory parameters measured in stable conditions FEV1, FEV1/FVC%, IC and PaO2, PaCO2 and BMI were chosen and their relationships with all-cause and respiratory mortality and with morbidity were assessed. Results: All these variables were associated with mortality at the univariate analysis. However, in a multivariate regression analysis (Cox proportional hazards model) for all-cause mortality age (year), IC (%pred.) and PaO2 (mmHg) remained the only significant, independent predictors (HR ¼ 1.056, 95%CI: 1.023–1.091; HR ¼ 0.981, 95%CI: 0.965–0.998; HR ¼ 0.948, 95%CI: 0.919–0.979, respectively). According to the same analysis, IC (%pred.) and PaO2 (mmHg) were significant independent predictors for respiratory mortality (HR ¼ 0.967, 95%CI: 0.938–0.997; HR ¼ 0.919, 95%CI: 0.873–0.969) together with FEV1/FVC% and BMI (kg/m2) (HR ¼ 0.967, 95%CI: 0.933–1.022; HR ¼ 0.891, 95%CI: 0.807–0.985, respectively). IC (%pred.), FEV1/FVC%, and PaO2 (mmHg) were also significantly related to morbidity, as independent predictors of hospital admissions because of exacerbations (OR ¼ 0.980, 95%CI: 0.974–0.992; OR ¼ 0.943, 95%CI: 0.922–0.987; OR ¼ 0.971, 95%CI: 0.954–0.996, respectively). Conclusion: IC (%pred.) is a powerful functional predictor of all-cause and respiratory mortality and of exacerbation-related hospital admissions in COPD patients.