Risk factors for prevalence of and mortality related to restriction on spirometry: findings from the First National Health and Nutrition Examination Survey and follow-up

OBJECTIVE: To define risk factors for both restriction on spirometry and subsequent mortality in a national cohort of US adults. METHODS: Participants in the First National Health and Nutrition Examination Survey (NHANES I) were followed for up to 22 years. Subjects were classified using the forced expiratory volume in one second (FEV1), the forced vital capacity (FVC), and the FEV1/FVC ratio into subgroups with and without restriction on spirometry. Regression models were developed to determine risk factors for restriction on spirometry and death. RESULTS: Our final cohort consisted of 4320 subjects, of whom 481 (10.3 weighted %) had restriction on spirometry. The largest risk factors for restriction on spirometry were a cardiothoracic ratio of \u3e55% (OR 4.3, 95%CI 3.1–5.9), race other than black or white (OR 3.7, 95%CI 1.8–7.8), and a history of stroke or paralysis (OR 1.8, 95%CI 1.1–2.9). The overall mortality rate was increased in subjects with restriction on spirometry (25.7 vs. 10.3 deaths per 1000 person-years). CONCLUSIONS: Restriction on spirometry is associated with comorbid disease and increased mortality, and is present in a significant proportion of the population