Effects of volatile anesthetics on vagal C-fiber activities and their reflexes in anesthetized dogs

Effects of halothane, enflurane, isoflurane, and sevoflurane on vagal capsaicin (CAPS)-sensitive C-fibers were elucidated in anesthetized dogs. The CAPS-sensitive C-fibers were significantly stimulated by all volatile anesthetics with a significantly greater response to halothane than with sevoflurane. A significant increase in respiratory frequency (fr) and a significant decrease in tidal volume (Vt) were observed with halothane and isoflurane, and a significant increase in fr was observed with sevoflurane. In contrast, a significant decrease in fr was induced by enflurane. The tachypnea induced by halothane, isoflurane, and sevoflurane was significantly reduced or no longer observed after perineural CAPS-treatment or bilateral vagotomy, whereas the slowing of respiration observed with enflurane was not affected by either of these treatments. These results suggest that vagal C-fibers play an important role in the reflex tachypnea that occurs with halothane, isoflurane, and sevoflurane. Copyright (C) 1998 Elsevier Science B.V.