A Reexamination of Risk Factors for Ventilatory Impairment

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Abstract
Previous cross-sectional analyses of data from the Tucson Epidemiological Study of Airways Obstructive Diseases have shown significant relationships of ventilatory impairment to a variety of risk factors, including smoking, chronic productive cough, a history of childhood respiratory illnesses, atopy, blood eosinophilla, and serum immunoglobulin E (IgE). In the present report, we examine these relationships in subjects 40 to 74 yr of age to determine the effect of excluding known asthmatics who, as a group, have markedly impaired lung function. After exclusion of asthmatics, atopy, eosinophilla, and IgE no longer appear to be significant risk factors for ventilatory impairment, and nonasthmatic nonsmokers show almost no remaining ventilatory impairment. In current smokers, quantitative relationships of FEV, to pack-years of cigarette consumption and to chronic productive cough are changed little by excluding asthmatics. in nonasthmatic ex-smokers, however, age at quitting smoking adds significantly to prediction of FEV, after accounting for pack-years. Young ex-smokers closely resemble nonsmokers, but they become increasingly similar to current smokers as their age at quitting increases. A history of respiratory trouble before 16 yr of age continues to appear to increases susceptibility to smoking effects, even after exclusion of asthmatics. But, as in previous studies, the possible bias of perferential recall of childhood illnesses by impaired subjects limits interpretation of this observation. On the other hand, present findings suggest that such factors as atopy, eosinophilia, and elevated serum IgE may well be risk factors for persistent asthma, but they have no relationship to nonasthmatic forms of chronic obstructive pulmonary disease (COPD). Thus, the "Dutch hypothesis" appears relevant primarily to a syndrome that has been called "chronic asthmatic bronchitis" but does not appear to apply to the more emphysematous forms of COPD that are characteristic of smokers without a know asthmatic background.