DIFFERENTIAL-EFFECTS OF DESFLURANE AND HALOTHANE ON PERIPHERAL AIRWAYSMOOTH-MUSCLE

Volatile anaesthetics have been shown to have direct relaxant effects on airway smooth muscle. We have examined the effects of 0.9, 1.9, and 2.8 dog MAC of desflurane and halothane on isolated proximal and dist al canine airways precontracted with acetylcholine. The proximal and d istal airway smooth muscle relaxed with increasing concentration of ea ch anaesthetic in a dose-related manner. Desflurane had a greater rela xant effect than halothane on the proximal airway only at 2.8 MAC. Des flurane relaxed the distal airway to a greater extent than halothane a t 1.9 and 2.8 MAC. The distal airway smooth muscle was more sensitive to volatile anaesthetics than the proximal airway smooth muscle with e ither halothane or desflurane at all concentrations tested. This effec t may be a result of differences in cartilage content, myosin content, epithelium-dependent effects, receptor density, myofilament sensitivi ty to Ca2+, sarcoplasmic reticulum Ca2+ control, or ionic fluxes in th e proximal airway compared with the distal airway. The increased sensi tivity of airway smooth muscle to desflurane compared with halothane i s not known but may be related to possible differences in the effects of Ca2+ homeostasis.