Diurnal variation of air and helium-oxygen flow-volume curves in asthmatic children.

In order to assess diurnal variation of flow-volume curves and to determine whether small airways are involved in the diurnal variation of pulmonary function in asthmatic children, we studied eight asthmatics who were attending an asthma summer camp. Spirometry and maximal expiratory flow-volume curves with air and a helium-oxygen mixture were obtained in the morning and afternoon over a 10-day period. We found that significant increases in maximal expiratory flows at all lung volumes occurred in the afternoon. However, the increase in flows with helium (helium response) was unchanged from morning to afternoon. These results suggest that both large and small airways are involved in the diurnal variation of pulmonary function in asthmatic children.