Airflow obstruction, cognitive function and mortality in a US national cohort: NHANES-III.

Abstract

To test the hypothesis that cognitive impairment increases mortality independent of airflow obstruction. In 1988-1994 the Third National Health and Nutrition Examination Survey (NHANES III) measured forced expiratory volume in the first second (FEV1) and the forced vital capacity (FVC) and selected items on cognitive function with mortality follow-up. For this survival analysis 4365 persons aged 60 and over with complete data formed the analytic sample. The FEV1/FVC less than the lower limit of predicted ratio (LLP) defined airflow obstruction and Composite Cognitive Function Score (CCF) ≤4, cognitive impairment. The percentage who died during follow up was 67% among those with neither FEV1/FVC < LLP nor CCF ≤4, 82% with FEV1/FVC < LLP only, 85% with CCF score ≤4 only and 93% with both FEV1/FVC LLP and CCF score ≤4 (P < .001). Weighted Cox proportional hazards regression revealed an increased hazard ratio (HR) in persons with FEV1/FVC <LLP only and in persons with CCF ≤4 only, respectively, compared with persons with neither. FEV1/FVC ratio < LLP remained a significant predictor of mortality with an interaction between FEV1/FVC ratio < LLP and CCF ≤4 (P = .051). Elderly persons with either airflow obstruction or cognitive impairment or both had increased all-cause mortality when compared to those with neither after adjusting for confounders. However, cognitive impairment was not a predictor of increased mortality independent of airflow obstruction.