A respiratory symptom questionnaire, conventional spirometric tests, and measurement of closing volumes were used to test 1,073 persons who attended an emphysema screening center. In 524 cigarette smokers, the following incidence of abnormalities of lung function were found. (1) Closing capacity expressed as a percentage of total lung capacity was abnormal in 44 per cent. (2) Closing volume expressed as a percentage of vital capacity was abnormal in 35 per cent. (3) Mean maximal expiratory flow measured from 25 to 75 per cent of forced expiratory volume was abnormal in 21 per cent, and (4) forced expiratory volume in one second was abnormal in 11 per cent. In both smokers and ex-smokers, there was a positive correlation between total cigarette consumption and the frequency of abnormalities in the lung function tests. Ex-smokers showed a significantly lower frequency of abnormalities of closing volumes but a greater frequency of abnormal FEV1 than smokers.
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Buist et al. (1973) studied this question.