Lung volume changes during histamine-induced bronchoconstriction in recurrently wheezy infants.

Respiratory inductance plethysmography was used to estimate changes in functional residual capacity (FRC) in seven recurrently wheezy infants undergoing histamine challenge. Inhalations of normal saline and doubling concentrations of histamine were given up to and including the provoking concentration (PC) that caused a significant fall in maximum flow at FRC (Vmax FRC) as measured using the inflatable jacket technique. Below the PC histamine in general caused small increases in FRC [9.4 +/- 7.6 ml (mean +/- SD) at half the provoking concentration]. However, larger increases were seen at the provoking concentration (26.6 +/- 15.6 ml). Inspection of flow-volume curves obtained before and after the larger changes in FRC suggested that the reduction in airflow measured by the change in Vmax FRC was underestimated.