Most tests of lung function used in the evaluation and follow-up of the pulmonary effect of smoking reflect airway function alone such as standard spirometry. Whereas, the best established test that reflect alveolar function is the single-breath carbon monoxide diffusing capacity (DLco-SB) especially when this is expressed per liter of alveolar volume (DLco/VA). Accordingly, to study the effect of smoking on both airway and alveolar functions, it is necessary to use DLco/VA test in addition to standard spirometry.
The present study was designed to evaluate the effect of cigarette smoking on lung diffusion, to correlate the effect of cigarette smoking and smoking cessation on lung diffusion and to find out whether the effect of cigarette smoking on lung diffusion is reversible.
SUBJECTS AND METHODS:
The effect of cigarette smoking on spirometric indicators of ventilatory function (FVC, FEV1%, PEFR) and on lung diffusing capacity for carbon monoxide (DLco-SB/VA) was evaluated on two occasions 6 months apart in 94 middle-aged, asymptomatic, male subjects, 56 smokers and 38 nonsmokers.
All subjects were within the normal predicted spirometric and lung diffusion values (80-120%). The values of FVC, FEV1, FEV1/FVC% and PEFR averaged more than 94% in never smokers (n = 38, mean age 43.57 years), 85% predicted in smokers (n = 56, mean age 42.54 years). However, the mean rate of decrease in spirometric and lung diffusion values (DLco/VA) between smoker and non-smokers were significant (p<0.05). fourteen subjects (14) who initially were smokers became sustained ex-smokers within six months of the first measurement, however, comparing the mean values of these parameters between the two groups reveals statistically significant differences (p<0.05); since that the values of DLco and DLco/VA in ex-smokers were significantly greater than those of current smokers and approached the values of those who had never smoked. In ex-smokers the mean values of DLco/VA rose, averaging 90% predicted at the first assessment but 97% predicted six months later.
The values of FVC, FEV1, FEV1/FVC%, PEFR and Lung diffusing capacity for carbon monoxide (DLco/VA) were lower in smokers than in never smokers. Ex-smokers had spirometric and lung diffusion values similar to those of never smokers even when spirometric values and DLco/VA were known to have been reduced while they were smoking.