Assessing the integrity of sympathetic pathways in spinal cord injury

STUDY DESIGN: Measurement of cutaneous sympathetic reflexes and hemodynamic responses to brief electrical stimuli applied above (forehead) and below (abdominal wall) a spinal lesion. OBJECTIVE: To assess the validity of using cutaneous vasoconstriction as a sensitive indicator of increases in sympathetic activity in spinal cord injury. SETTING: Prince of Wales Medical Research Institute, Australia. SUBJECTS: Twenty spinal cord injured subjects with injuries ranging from C3-T11 and nine able-bodied controls. METHOD: Cutaneous electrical stimulation was applied to the forehead and abdominal wall to subjects at unexpected times. Sudomotor and vasomotor responses, as well as continuous arterial pressure, heart rate and respiration were monitored. RESULTS: Sudomotor (electrodermal) responses to forehead stimulation were scarce in spinal cord injured subjects, whereas cutaneous vasoconstrictor responses (photoelectric pulse plethysmography) provided a sensitive indicator of any remaining central control of sympathetic function below the lesion. Electrical stimulation applied to the abdominal wall evoked vasoconstrictor reflexes below the lesion in the majority of spinal cord injured subjects, whereas only a limited number of electrodermal responses were observed. That these cutaneous vasoconstrictor responses could reflect parallel increases in muscle and splanchnic vasoconstrictor activity was indicated by the increases in blood pressure; patients lacking vasoconstrictor responses rarely showed stimulus-induced blood pressure increases. CONCLUSION: Our findings show that skin vasomotor responses to somatosensory stimulation provide a more sensitive tool than electrodermal responses for evaluation of sympathetic function below a spinal cord lesion. STATEMENT OF ETHICS: We certify that all applicable institutional and governmental regulations concerning the ethical use of human volunteers were followed during the course of this research, and all experiments were conducted with the understanding and consent of each subject.