The contributions of rib cage and abdominal displacements to the hyperinflation of acute bronchospasm.

To quantitate the relative contributions of rib cage and abdomen to the hyperinflation of asthma, we examined chest wall movements during histamine-induced bronchospasm in 7 male asthmatic subjects. A reduction in FEV1 of 28.1 +/- 4.5% (mean +/- 1 SE) was associated with an increase in functional residual capacity (FRC) of 0.99 +/- 0.19 L, as measured by spirometer. Similar increases in FRC (0.91 +/- 0.18 L) were obtained using a DC respiratory inductive plethysmograph (RIP). The absolute error of measurement of delta FRC by RIP, compared with that by the spirometer, was 23.0 +/- 1.9%. The delta FRC by RIP was slightly less than by spirometer, as indicated by a net positive error of 7.2 +/- 7.3%. Increase in the volume of the rib cage, measured by RIP, usually accounted for the major change in FRC (75%). Even though the contribution of rib cage displacement to delta FRC ranged from as little as 30% to as much as 100% of the change in individual subjects, it was correlated with the rib cage contribution to the tidal breath prior to bronchoconstriction. We conclude that the relative contributions of rib cage and abdominal displacements to the volume of hyperinflation during mild to moderate acute induced bronchoconstriction are quite variable, but they can be predicted from the relative contributions of these compartments to tidal breathing prior to bronchoconstriction.