The effect of differential and complete nerve block on experimental muscle pain in humans.
We have attempted to examine the nerve fiber population mediating experimentally induced muscle pain in humans. Two established methods induced muscle pain: continuous, intramuscular, electrical stimulation and intramuscular infusion of hypertonic saline. A progressive nerve block was achieved by a combination of compression nerve block and intravenous regional anesthesia. Regular tests of muscle pain intensity were performed during the blocking period of 60 min. At the same time, the blocking of thick and thin afferents was monitored by assessment of proprioception and cutaneous touch, pin-prick, pressure pain, and heat-detection thresholds. Electrically induced muscle pain was inhibited (P < 0.0001) in parallel with proprioception, touch, and pin-prick, which were mediated by thick and thin myelinated nerve fibers. Saline-induced muscle pain was inhibited (P < 0.002) synchronously with heat detection and pressure pain, which are mediated by unmyelinated nerve fibers. Based on the present psychophysical experiments, it is suggested that: (1) myelinated afferents mediated mainly electrically induced muscle pain, and (2) unmyelinated afferents mediated mainly saline-induced muscle pain.
Laursen
R J
RJ
Laboratory for Experimental Pain Research, Center for Sensory-Motor Interaction, Aalborg University, Fredrik Bajers Vej 7 D-3, DK-9220 Aalborg O, Denmark. rjl@miba.auc.dk
Graven-Nielsen
T
T
Jensen
T S
TS
Arendt-Nielsen
L
L
D000328:Adult; D000779:Anesthetics, Local / Q000008:administration & dosage; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D006982:Hypertonic Solutions; D007273:Injections, Intramuscular; D008012:Lidocaine / Q000008:administration & dosage; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation* / Q000503:physiopathology*; D009407:Nerve Block; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D010146:Pain / Q000139:chemically induced / Q000188:drug therapy / Q000503:physiopathology*; D011312:Pressure; D011434:Proprioception / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology; D012965:Sodium Chloride; D014110:Touch / Q000502:physiology
D000779:Anesthetics, Local; D006982:Hypertonic Solutions; D012965:Sodium Chloride; D008012:Lidocaine