Two types of spontaneous electrical activity are present at the end-plate zone: low-voltage negative potentials that correspond to miniature end-plate potentials, and larger voltage negative-positive potentials. The electrogenic origin of the latter has been uncertain. The origin of these larger potentials was investigated in the rat phrenic nerve diaphragm preparation and in human gastrocnemius muscle just prior to intubation during administration of preoperative anesthesia. In the hemidiaphragm the larger voltage negative-positive potentials were rarely triggered by intracellular or tungsten microelectrodes. The negative-positive potentials, however, were clearly triggered by contact of the concentric needle electrode with muscle hemidiaphragm at the end-plate region. The potentials were abolished by curare. Likewise, the equivalent potentials observed at the human gastrocnemius end-plate zone were blocked by neuromuscular blocking agents. Therefore, these positive-negative discharges represent postsynaptic muscle fiber action potentials and not nerve fiber activity. They were probably presynaptically activated by mechanical irritation of the motor axon terminal and preterminal branches.

To assess the efficacy of 4% topical lidocaine in spheno-palatine blocks, a randomized controlled trial was carried out on patients with chronic muscle pain syndromes. Sixty-one patients (42 with fibromyalgia (FM) and 19 with myofascial pain syndrome (MPS)) completed the trial. Outcome measures included pain intensity, a daily pain diary, headache frequency, sensitivity to pressure using a dolorimeter, anxiety, depression, and sleep quality. Patients were randomized to receive either 4% lidocaine or sterile water (placebo) 6 times over a 3-week period. Both subjects and investigators were blind to treatment allocation. The results showed that 4% lidocaine had no superiority over placebo in any of the outcome measures. Twenty-one subjects (35%) showed a decrease in pain which was greater than 30% of their baseline value. Of these 21 subjects, 10 received lidocaine and 11 received placebo. These data suggest that, in this population, 4% lidocaine is no better than placebo in the treatment of chronic muscle pain.

No abstract

Limb ischaemia induced by a sub-maximum effort tourniquet technique was used to characterize the analgesic effects of lumbar epidural morphine in volunteers. As an index of pain threshold, we measured the time to perception of pain in an upper and a lower limb before and at intervals up to six hours following epidural injections of morphine 3.5 mg and 7.0 rag, and before and after subcutaneous injections of the same doses. Subcutaneous morphine had no significant effect on the times to perception of pain in either limb. Lumbar epidural morphine did not alter upper limb times, but markedly delayed the onset of pain in the lower limbs. This lower limb analgesic effect was apparent thirty minutes after injection, peaked at about ninety minutes and was still present after six hours. Serum levels of morphine were nearly identical after subcutaneous and epidural injections of the same dose. We conclude that lumbar epidural morphine produces marked analgesia for this type of experimental pain primarily by a "'regional" effect rather than as a result of systemic absorption. This regional effect develops slowly and is prolonged.KEY WORDS: ANALGESIA, Epidural morphine, regional effect.ALTHOUGH A SPINAL ACTION of narcotics had been suspected for many years, ~ it was only recently discovered that small doses of narcotic placed directly into the sub-arachnoid space of animals could produce behavioural analgesia,-' apparently by binding to specific receptors in the dorsal horn of the spinal cord, 3.~ and so reducing central transmission of peripheral noxious stimulP -x.Both intrathecal and epidural morphine have now been carefully tested for analgesic effectiveness in human patients with pathological pain. In double-blind cross-over studies employing placebo controls, lumbar intrathecal morphine 0.5-1.0 mg was observed to relieve severe "'intractable" pain associated with cancer of the pelvis, ~ and lumbar epidural morphine 2-6 mg to reduce pain after upper abdominal surgeryJ ~ In each case. the quality of analgesia was better than that associated with commonly used intramuscular doses of morphine. 9'~~ For extended analgesic therapy, the epidural route of administration would be preferred to the intrathecal, as it avoids the added risks associated with repeated subarachnoid punctures.There is only limited information on the pharmacokinetics and pharmacodynamics of epidurally administered narcotic. Preliminary data suggest that after epidural injections of morphine and meperidine in man, narcotic appears in the lumbar cerebrospinal fluid (CSF) within minutes, with local CSF concentrations becoming maximal in about 30 minutes. TM The analgesia produced is reported to be "regional" or "segmental" in nature, ~3-~5 but its onset, magnitude and duration are unclear, seeming to vary considerably between individual patients -perhaps partly dependent upon the origin and type of pain being treated and, in some instances, the clinical condition in which pain has occurred. ~ :'t 6.~ 7The purpose of this study was to examine in a...

No abstract