Lung resistance (RL) was measured using FlexiVent system in response to: (A), increasing doses of computer-controlled nebulized methacholine (MCh), (B), dynamic lung compliance (Cdyn), which reflects lung compliance at any given time during actual movement of air. Determination of RL and Cdyn was carried after Af-sensitization as described in Methods. The results are representative of two different sets of inhalation exposures. Data are expressed as mean ± SD (n = 6 –17/group). * ≤ p = 0.05; FA = filtered air, SS = sidestream cigarette smoke; F1: first generation; F2 second generation.