CO DIFFUSING-CAPACITY IN A GENERAL-POPULATION SAMPLE - RELATIONSHIPS WITH CIGARETTE-SMOKING AND AIR-FLOW OBSTRUCTION

The single-breath carbon monoxide diffusing capacity (DL(COsb)) was me asured together with ventilatory lung function tests as part of a surv ey of a general population sample living in Northern Italy (n = 2,481) . Based on answers to an interviewer-administered questionnaire, subje cts free of respiratory symptoms or diseases were identified. Data fro m subjects who had never regularly smoked cigarettes were used to deri ve reference equations for the test indexes, and data from the remaini ng subjects who had smoked were used to derive regression equations in corporating a term expressing cigarette consumption (cube root of pack -years) and a term indicating current smoking decrement, in order to o btain expected DL(COsb) percent predicted. Neither number of cigarette s smoked daily or duration of smoking, in smokers, nor duration of smo king or years since quitting smoking, in ex-smokers, entered significa ntly the multiple-regression model. The mean values of DL(COsb) were o nly slightly affected by the increasing degree of airway obstruction. When subjects with confirmed asthma were analyzed, after stratifying f or different levels of FEV1/FVC ratio, increased mean value of DL(COsb ) (over 100%) was found in those with an FEV1/FVC ratio between 75 and 65%. This cross-sectional analysis suggests that there is a decrease in DL(COsb) with cumulative cigarette consumption even in healthy subj ects. Further, it confirms the clinical observations of high DL(COsb) values in asthmatic patients, at least in those with an initial degree of chronic airflow obstruction.