Ventilation distribution during histamine provocation

We investigated ventilation inhomogeneity during provocation with inhaled histamine in 20 asymptomatic nonsmoking subjects. We used Nz multiple-breath washout (MEW) to derive parameters S-cond and S-acin as a measurement of ventilation inhomogeneity in conductive and acinar zones of the lungs, respectively. A 20% decrease of forced expiratory volume in 1 s (FEV1) was used to distinguish responders from nonresponders. in the responder group, average FEV1 decreased by 26%, whereas S-cond increased by 390% with no significant change in S-acin. In the nonresponder group, FEV1 decreased by 11%, whereas S-cond increased by 198% with no significant S-acin change. Despite the absence of change in S-acin during provocation, baseline S-acin was significantly larger in the responder vs. the nonresponder group. The main findings of our study are that during provocation large ventilation inhomogeneities occur, that the small airways affected by the provocation process are situated proximal to the acinar zone where the diffusion front stands, and that, in addition to overall decrease in airway caliber, there is inhomogeneous narrowing of parallel airways.