Figure 1. Concentrations of inhaled acetylcholine necessary for a 20% decrease of forced expiratory volume in 1 s. Y-axis shows acetylcholine concentrations, X-axis lidocaine (A, left) or bupivacaine (B, right) concentrations, respectively. Each symbol represents the response of one volunteer subjected to an inhalational challenge during intravenous infusion of placebo (open symbols) or three different doses of either lidocaine or bupivacaine (full symbols). The individual plasma concentrations with the corresponding acetylcholine thresholds are shown for each challenge. The local anesthetics were administered as described in methods. The inhalational challenges were performed on 7 different days. Each increase in the plasma concentration of the local anesthetic resulted in a corresponding increase in the acetylcholine threshold. Thus, both local anesthetics dose-dependently increased the acetylcholine threshold in volunteers with bronchial hyperreactivity.