Topographical Differences in the Direct Effects of Isoflurane on Airway Smooth Muscle

摘要: Volatile anesthetics have a direct relaxant effect on airway smooth muscle, but it is not known whether this similar throughout the bronchial tree. We studied relaxation of isoflurane isolated proximal (outer diameter [OD] 4–6 mm) and distal (OD 0.7–1.5 canine airways precontracted with acetylcholine. Proximal rings were suspended in tissue baths stretched to their optimum length. A dose-response curve was obtained for each ring log increments Maximum contraction reached 10 −2 mol/L acetylcholine muscle (7.0 ± 0.3 g tension) −3 (2.3 0.1 tension). Based curve, ED50 calculated (1.26 0.37 × −4 muscle; 2.12 1.14 −5 muscle) administered bath, after which stabilized response recorded. randomly selected dose (1,2, or 2.6 dog minimum alveolar anesthetic concentration [MAC]) then bath responses The relaxed increased doses dose-related manner. average three times greater than at all levels. mechanism differential known, may be due an epithelium dependent effect, sensitivity contractile elements Ca2+; and/or differences ionic fluxes.