Bronchoconstriction-induced hyperinflation assessed by thoracic area measurement in guinea pigs.

The changes in end-expiratory lung volume (EELV) accompanying histamine-induced bronchoconstriction were compared for two routes of drug administration in anesthetized, paralyzed, and mechanically ventilated guinea pigs. Changes in EELV were estimated from measurements of thoracic cross-sectional area, assessed from the voltage induced by an external uniform magnetic field in a pickup coil encircling the rib cage. Increasing doses of histamine were administered as bolus injections in Group 1 (n = 7) and as nebulizations in Group 2 (n = 7). After each bronchial challenge, the maximum change in EELV and the associated intrinsic positive end-expiratory pressure (PEEPi) were measured at the same time. In both groups, bronchoconstriction was accompanied by an increase in EELV, which was related to the degree of bronchoconstriction and reached about 70 to 100% of the basal functional residual capacity. The increases in EELV were linearly related to the PEEPi values (p < 0.001) and did not depend on the route of histamine administration. These results indicate that dynamic hyperinflation is not the only mechanism involved in lung volume response to bronchoconstriction and suggest that gas trapping may have occurred in alveolar spaces.