Carbon Monoxide Diffusing Capacity, Other Indices of Lung Function, and Respiratory Symptoms in a

SUMMARY To assess the relationships among single-breath diffusing capacity for CO (OLeosb) (13), respiratory symptoms, and cigarette smoking in a general population sample, the data of 718 men and 894 women 20 yr of age or older were analyZed, and comparisons were performed with flow-volume curve (MEFV) variables and the slope of the alveolar plateau (ON2%/L) as well. Percent predicted OLeosb and its correction for alveolar volume (OLIVA)were significantly lower In smokers than in nonsmokers. The relationship of presence/absence of respiratory symptoms and cigarette smoking with DLeosb and OLIVAwas significant. Oleo indices were almost alWaysselected as dis­ criminant variables in multivariate analysis between asymptomatic and symptomatic subjects. Poor concordance among lung function tests was evident: in men, 30% with abnormal (i.e., lower than 97.5% percentile) and 21% with normal OLeo Indices also had abnormal MEFV parameters and/or ON2%/L. In women, the corresponding figures were 24 and 10%, respectively. In men, when con­ sidering only Oleo indices, the percentage of symptomatic subjects with abnormal lung function tests ranged from 33% in those with at least one symptom to 45% in those complaining of dyspnea. When the proportion of symptomatic SUbjects with ON2%/L and MEFV abnormalities were added, it increased to 56 and 66%, respectively. However, in women the proportion of symptomatic SUbjects with abnormal lung function indices was very small. These results Indicate the usefulness of includ­ ing CO diffusing capacity in epidemiologic surveys in the detection of abnormalities.