STUDY ON THE CHANGE OF INTRACARDIAC CONDUCTION SYSTEM AND ITS MECHANISM DURING EPIDURAL ANALGESIA

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The effects of epidural analgesia with opioids and clonidine, one of the alpha-2 agonists, during general anesthesia on cardiac and renal sympathetic nerve activity and intracardiac conduction were studied in the cats. Thoracic epidural administration of morphine during alpha-chloralose anesthesia dramatically decreased sympathetic nerve activity and attenuated sinus nodal and AV nodal functions. Alomost the same effects were observed with epidural morphine in the cat baroreceptor nerves and vagal nerves were sectioned. Lumbar epidural administration of morphine has shown the same effect as thoracic epidural administration, so epidural morphine was supposed to spread extensively in CSF and act not only on spinal cord but also brainstem. This was probably due to the hydrophilic property of morphine. Epidural fentanyl or meperidine also depressed sympathetic nerve activity and intracardiac conduction, however showed a segmental depression of sympathetic activity. These depressions with meperidine were only partially reversed with intravenous naloxon.Epidural clonidine, one of the alpha-2 agonists, also showed decrease in sympathetic nerve activity and attenuation of sinus nodal and AV nodal functions. The dose effect of epidural clonidine was not linear, which was maximal at 4 microgram/kg.