Changes in functional residual capacity in response to bronchodilator therapy among young asthmatic children.

Measurements of functional residual capacity (FRC) by helium gas dilution and peak expiration flow rate (PEFR) were made in 63 young asthmatic children aged 2 and 7 years before and after bronchodilator therapy. All 63 children tolerated two measurements of FRC, but only 33 children were able to perform the peak flow maneuver. Bronchodilator therapy was associated with significant change in FRC in the majority (80%) of children; in some, however, this change was an increase rather than a decrease. The change in FRC was significantly correlated with both prebronchodilator FRC and the change in PEFR. An increase in FRC following bronchodilator therapy was more common in children with severe and symptomatic asthma. We suggest that changes in FRC may be used in asthmatic children to demonstrate bronchodilator responsiveness, particularly in those too young to perform other respiratory function tests.