An Integrated Index Combined by Dynamic Hyperinflation and Exercise Capacity in the Prediction of Morbidity and Mortality in COPD

BACKGROUND: Dynamic hyperinflation (DH) and exercise limitation develop in patients with COPD; however, there is lack of knowledge about their long-term clinical consequences. We aimed to assess the impact of DH and exercise capacity in predicting mortality and also morbidity, as evaluated by emergency visits and hospital admissions in COPD patients during a 4-year period. METHODS: We recruited 73 stable COPD patients. The relationships of different respiratory parameters (FEV1 %, body mass index, 6 min walk test distance [6MWD], static hyperinflation as measured by the ratio of inspiratory capacity to total lung capacity (IC/TLC) at rest, DH as measured by the change between the post- and pre-exercise values of IC/TLC [Delta IC/TLC], P-aO2, and P-aCO2) with emergency visits and hospital admissions because of exacerbations and also with respiratory and all-cause mortality were assessed. RESULTS: The median follow-up period was 47 months (IQR 45-48 months, n = 73). During the follow-up there were 8 (11%) deaths. The Delta IC/TLC value was 3.9 +/- 4.6%. The Kaplan-Meier survival curve showed that the cumulative survival rate was significantly lower in the patients with Delta IC/TLC > 4 and with 6MWD <= 439.56 m, using these values as thresholds. (The rates for sensitivity were 100% and 87.5%, and for specificity were 56.92% and 87.69%, respectively). The Cox proportional hazards model showed that DH (hazard ratio = 1.4,95% CI = 1.09-1.84, P = .009) and 6MWD (hazard ratio = 0.98, 95% CI = 0.97-0.99, P = .006) were independent predictors of all-cause and respiratory mortality. 6MWD, FEV1%, IC/TLC, and Delta IC/TLC were found to be significantly related to emergency visits (r = -0.28, r = -0.41, r = -0.24, and r = 0.38, respectively) and hospital admissions (r = -0.41, r = -0.45, r = -0.36, and r = 0.28, respectively). CONCLUSIONS: DH and exercise capacity are reliable and independent predictors for mortality and morbidity in COPD patients. We propose that DH and exercise capacity be considered in the assessment of long-term clinical consequences of COPD patients.