Longitudinal methods for describing the relationship between pulmonary function, respiratory symptoms and smoking in elderly subjects: The Tucson Study

In this study recently developed longitudinal techniques are used to examine the relationship between respiratory symptoms, smoking and pulmonary function measures in elderly subjects. The subjects were participants in the Tucson Epidemiological Study of Airways Obstructive Disease, aged ≥55 yrs at the first survey 1972-1973, who had received pulmonary function testing and completed questionnaires in at least one of the six selected surveys. There were 633 males and 891 females, with up to 14 yrs follow-up included in the analysis. Based on their questionnaire responses, subjects were classified according to their respiratory symptoms and smoking habits at each survey. The pulmonary function testing included forced vital capacity (FVC), forced expiratory volume in one second (FEV₁), and their ratio (FEV₁/FVC). The pulmonary function data were analysed gender specific, with and without stratifying on vital status. The results indicate that respiratory symptoms are generally associated with lower levels of lung function, and that the impairment associated with chronic cough was observed predominantly in male subjects. The negative association of smoking was apparent in most measures, but was largest and most progressive in the FEV₁/FVC ratios. Ex-smokers, in all cases, had better lung function values than current smokers, but their mean curves were always significantly below the values of nonsmokers.