Figure 5. Relationship of resting diameter to local and conducted response. The data presented in Figure 2, Figure 3, Figure 4were normalized as discussed in methods. This was done to determine if decreased responses to methacholine could be explained completely by the changes in resting diameter. The effects of increased resting diameter caused by decreasing the oxygen concentration were compared with those caused by applying anesthetic agents. The data for local and conducted response ratios for oxygen (open triangles) are grouped into ranges of resting diameter increases. The data for local and conducted response ratios for halothane (filled circles) and isoflurane (filled squares) are grouped by anesthetic concentration (C = control, 1%, 2%). (A) Normalized local dilations caused by methacholine versus normalized changes in resting diameter. The effect of resting diameter was not significantly different between any treatments (oxygen, halothane, or isoflurane). (B) Normalized conducted dilations versus normalized changes in resting diameter. Analysis of variance of these normalized data showed significant differences in the way the resting diameter affected the conducted response (P = 0.0063) depending on the treatment. Therefore, volatile anesthetic agents affected conducted dilations significantly more than could be explained by a changes in resting diameter (as defined by lower oxygen).