Selective activation of muscle and skin nociceptors does not trigger exaggerated sympathetic responses in spinal-injured subjects.
METHODS
Measurement of sympathetic effector organ responses to selective activation of muscle and skin nociceptors below lesion in spinal cord-injured (SCI) subjects.


OBJECTIVE
To test whether selective noxious stimulation below lesion causes exaggerated sympathetic responses in human SCI.


METHODS
Prince of Wales Medical Research Institute, Australia.


METHODS
Twelve subjects (C5-T10, ASIA A-C), none of whom had sensation below the lesion, were included in the study. Selective stimulation of muscle or cutaneous nociceptors was produced by bolus injection of hypertonic (5%) saline into the tibialis anterior muscle or overlying skin and compared with non-noxious electrical stimulation of the abdominal wall. Cutaneous vasoconstrictor (photoelectric plethysmography) and sudomotor (skin conductance) responses, in addition to respiration, heart rate and continuous arterial pressure were monitored.


RESULTS
Electrical stimulation of the abdominal wall caused a significant increase in arterial pressure (31.8+/-6.1%). Conversely, intramuscular or subcutaneous injection of hypertonic saline caused no significant changes in blood pressure (-3.0+/-2.4%; -1.4+/-3.4%) heart rate, skin blood flow or sweat release.


CONCLUSIONS
While hypertonic saline injected into muscle or skin induces strong pain, cutaneous vasoconstriction and sweat release in able-bodied subjects, we saw no evidence of exaggerated sympathoexcitation when these same noxious stimuli were delivered below lesion in subjects with SCI. This suggests that certain types of somatic noxious input may not trigger autonomic dysreflexia, and questions the concept that any painful stimuli originating below lesion can reliably trigger dysreflexia.
Burton
A R
AR
Spinal Injuries Research Centre, Prince of Wales Medical Research Institute and University of New South Wales, Sydney, New South Wales, Australia. a.burton@powmri.edu.au
Brown
R
R
Macefield
V G
VG
D000328:Adult; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D004558:Electric Stimulation / Q000379:methods; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009132:Muscles / Q000187:drug effects / Q000294:innervation* / Q000528:radiation effects; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D012039:Regional Blood Flow / Q000187:drug effects; D012462:Saline Solution, Hypertonic / Q000009:adverse effects; D012867:Skin / Q000098:blood supply / Q000187:drug effects / Q000294:innervation*; D013119:Spinal Cord Injuries / Q000473:pathology* / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000503:physiopathology*
D012462:Saline Solution, Hypertonic