Vagomimetic Effects of Morphine and Innovar® in Man

EVERAL animal studies have shown the S effects of narcotics, especially morphine, on heart rate (HR), suggesting vagal stimulation.1-5 According to these studies, morphine produces a slowing in HR as a result of both vagal stimulation and sympathetic depression. The present study was undertaken to determine whether morphine or Innovar,@ a widely used mixture which includes the synthetic narcotic fentanyl, has a vagal-stimulant effect in man. If narcotics have this effect, it is reasonable to expect that more atropine would be required to achieve a desired rise in HR. One might also assume that, since atropine in small doses is reported to produce vagal stimulation,6 such small doses in patients given narcotics would further reduce the HR. Larger doses of atropine, however, would be expected to block the cardiac vagal endings and overcome any vagomimetic influence of the narcotics.