Pulmonary Diffusing Capacity in Cigarette Smokers

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Abstract
The pulmonary diffusing capacity was measured by the single breath carbon monoxide technique in 79 healthy adult subjects of comparable age and body size. Over one-half had smoked 20 or more cigarettes daily for a varying number of years, the remainder never having smoked. The mean pulmonary diffusing capacity in the nosmokers was found to be 33.1 milliliters of carbon monoxide per minute per millimeter of mercury and in those who had smoked ten years or longer, it was 24.9 milliliters. The difference is highly significant (p = < .001). Other measurements of pulmonary function were normal and comparable in both the smokers and nosmokers thus eliminating abnormalities in ventilation and lung volumes as a cause for the differences observed in diffusing capacity. The average age of all subjects was 27.5 years; it probably accounts for the variance of these findings with those of others who have shown abnormalities in ventilation and lung volumes in heavy cigarette smokers in older age groups. The presence of carboxyhemoglobin in mixed venous blood as a result of heavy cigarette smoking was judged not to be altering the diffusion values since the single breath technique of measuring carbon monoxide diffusing capacity is probably not influenced significantly by venous carboxyhemoglobin. Slight impairment of the carbon monoxide diffusing capacity in heavy smokers as compared with nosmokers appeared after five years of smoking but became more significant following ten years of smoking. It is suggested that pathological changes in the alveolar septum due to the irritating effects of inhaled cigarette smoke may be the cause of this impairment.