Inspiratory capacity predicts mortality in patients with chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) severity is usually graded upon the FEV(1) reduction and FEV(1) has been considered the most important mortality predictor with age in COPD. Recent studies suggest other factors as more powerfully related to mortality than FEV(1) in COPD patients.

To assess the impact of inspiratory capacity (IC) on mortality and morbidity in COPD patients during a 5-year follow-up period.

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 FEV(1), FEV(1)/FVC%, IC and PaO(2), PaCO(2) and BMI were chosen and their relationships with all-cause and respiratory mortality and with morbidity were assessed.

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 PaO(2) (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 PaO(2) (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 FEV(1)/FVC% and BMI (kg/m(2)) (HR=0.967, 95%CI: 0.933-1.022; HR=0.891, 95%CI: 0.807-0.985, respectively). IC (%pred.), FEV(1)/FVC%, and PaO(2) (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).

IC (%pred.) is a powerful functional predictor of all-cause and respiratory mortality and of exacerbation-related hospital admissions in COPD patients.