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=1.056, 95%CI: 1.023-1.091; HR=0.981, 95%CI: 0.965-0.998; HR=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=0.967, 95%CI: 0.938-0.997; HR=0.919, 95%CI: 0.873-0.969) together with FEV₁/FVC% and BMI (kg/m²) (HR=0.967, 95%CI: 0.933-1.022; HR=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=0.980, 95%CI: 0.974-0.992; OR=0.943, 95%CI: 0.922-0.987; OR=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.