Association of reduced total lung capacity with mortality and use of health services.

Background: Pulmonary restriction is associated with increased mortality in adults, especially those who are elderly. Previous studies, however, have used the FVC as a surrogate for the total lung capacity (TLC). We evaluated the association between a reduced TLC, mortality, and health-care resources use and compared this association with a reduced FVC.

Methods: Seven hundred fifty-two patients > 60 years old and undergoing spirometry were recruited. The main analyses were performed in patients without bronchial obstruction (n = 405). Data on mortality and admission to acute care hospitals were derived. Pulmonary restriction was alternatively defined as a TLC or an FVC below the lower limit of normal (LLN). The unadjusted relative risk of mortality associated with pulmonary restriction and adjusted incidence rate ratios (IRRs) were determined. Survival analysis was repeated using time to first hospital admission as the dependent variable.

Results: Overall mortality was significantly higher in the group with reduced TLC compared with the group with lower FVC (10.2 per 100 patients vs 4.27 per 100 patients, respectively), with mortality rate ratios of 6.87 (95% CI, 2.54-18.24) and 2.73 (95% CI, 1.04-7.66), respectively. After adjustment, the hazard ratio (HR) for mortality associated with pulmonary restriction in patients who received diagnoses using the FVC was reduced to 2.05 (95% CI, 0.70-6.02). Reduced TLC remained strongly associated with mortality (HR, 4.52; 95% CI, 1.32-15.51). No association was found between restriction (diagnosed using either parameter) and risk for hospitalization.

Conclusions: Reduced TLC is strongly associated with mortality in adults who are elderly. Reduction of the FVC is a weaker risk factor for mortality.