PULMONARY-FUNCTION LEVELS AS PREDICTORS OF MORTALITY IN A NATIONAL SAMPLE OF US ADULTS

Single breath pulmonary diffusing capacity for carbon monoxide (DLCO) was examined as a predictor of all-cause mortality among 4,333 subject s who were aged 25-74 years at baseline in the First National Health a nd Nutrition Examination Survey (NHANES I) conducted from 1971 to 1975 . The relation of the percentage of predicted DLCO to all-cause mortal ity was examined in a Cox proportional hazard model that included age, sex, race, current smoking status, systolic blood pressure, serum cho lesterol, alcohol consumption, body mass index, percentage of predicte d forced vital capacity (NC), and the ratio of forced expiratory volum e at I second (FEV1) to FVC. Mortality had a linear association with t he percentage of predicted FVC (rate ratio (RR) = 1.12, 95% confidence interval (CI) 1.08-1.17, for a 10% decrement) and a significantly non linear association with the percentage of predicted DLCO with an adver se effect that was clearly evident for levels below 85% of those predi cted (RR = 1.24, 95% CI 1.12-1.37 for a 10% decrement). The relative h azard for the percentage of predicted DLCO below 85% was not modified by sex, smoking status, or exclusion of subjects with clinical respira tory disease on the initial examination. This association with the per centage of predicted DLCO, was present among 3,005 subjects with FEV1 levels above 90% of those predicted. Thus, pulmonary diffusing capacit y below 85% of predicted levels is a significant predictor of the all- cause mortality rate within the general US population independent of s tandard spirometry measures and even in the absence of apparent clinic al respiratory disease.