Pulmonary diffusing capacity as a function of lung volume in healthy and asthmatic children

Pulmonary diffusing capacity for carbon monoxide and lung volumes were measured in 167 healthy and 63 asthmatic children. Diffusing capacity was found to be best correlated with total lung capacity. There was no significant difference between the regression lines of diffusing capacity in the two groups. Thus, the higher than predicted diffusing capacity values observed in asthmatic children were directly proportional to the relatively large lung volumes found in this group. These results suggest that in symptom free asthmatic children, the increase in lung volume is achieved by addition of new alveoli of normal size rather than by enlargement of existing ones.