Confirmation: LASER application to the cervical spine in the absence of pathology has no effect on sympathetic nervous system outflow

Abstract

To verify response mechanisms and the feasibility of clinical models of pain research, the effect of laser phototherapy on neurophysiological pain mechanisms needs to be determined first in the absence of pathology. A randomized, placebo-controlled, double-blind, repeated measures study was undertaken to investigate the possible involvement of the sympathetic nervous system (SNS) following laser irradiation. Nineteen healthy subjects participated in a study that consisted of 5 treatments to the right posterior neck region at a dose of 4.0 J/cm2, using 820 nm laser. Each subject received active laser, placebo laser and a control condition over a three-day period, with a minimum of one day between sessions. Heart rate, blood pressure, bilateral skin temperature and skin conductance were measured distally. Results indicated that there was no alteration in sympathetic outflow, with no change in any of the outcome variables. It was concluded that in the laser phototherapy strategy used in this study, no effect on SNS outflow occurs in normal subjects. The model described raises the prospect for continuing research in clinical models of pain to determine if the SNS is involved in pain mediation subsequent to laser irradiation.