USE OF TESTS OF PERIPHERAL LUNG-FUNCTION FOR PREDICTING FUTURE DISABILITY FROM AIR-FLOW OBSTRUCTION IN MIDDLE-AGED SMOKERS

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Abstract
Tests of peripheral lung function were carried out in 1974 and again in 1975 on 263 healthy working men (205 current smokers and 58 lifelong nonsmokers) using a variety of proposed sensitive tests (maximal expiratory flow-volume curves, single-breath N2 test, CO diffusing capacity and arterialized capillary blood PO2 [partial pressure of O2]). The promise of these tests for the early detection of chronic airflow obstruction was assessed in various ways. Technical difficulties were assessed by studying the degrees to which the results of the various tests were affected by recent respiratory infections and by assessing the reproducibility of the test results at an interval of 1 yr. An ideal test should identify the same men in 1974 and in 1975 as being abnormal. An informative test of chronic airflow obstruction must yield results that are systematically worse in middle-aged smokers than in middle-aged nonsmokers, and such a test is likely to yield results that are correlated with the 1 s forced expiratory volume among midde-aged smokers. The analyses of the effects of respiratory infections, the reproducibility, the effects of smoking and the correlation with 1 s forced expiratory volume indicated that the most informative and repeatable tests were the maximal flow when 25% of the vital capacity remained to be expired and the N2 slope. These 2 tests seem the most promising adjuncts to the 1 s forced expiratory volume, as measures of early chronic airflow obstruction in middle-aged smokers and as predictors of future disability due to advanced disease if smoking continues. Their actual predictive value still requires direct assessment by follow-up of a large sample of middle-aged smokers for 10 or even 20 yr.