Effect of exercise on lung transfer factor for CO in smokers.

The lung transfer factor for carbon monoxide was studied in 24 apparently healthy smokers and in 24 well-matched non-smokers at rest and during exercise. Single-breath and steady state (TLcoss) transfer factors for carbon monoxide, the Krogh constant, and the capillary blood volume were significantly lower in smokers. Exercise increased minute ventilation to a similar extent in both groups, but significantly lower values of TLcoss were measured in smokers than in non-smokers during mild and moderate grades of exercise (p less than 0.001). This difference in TLcoss may be attributed either to the difference in capillary blood volume or to increased inhomogeneities with regard to alveolar ventilation and perfusion due to airway damages in smokers, or to both factors.