Effects of electric stimulation on C and A delta fiber-mediated thermal perception thresholds

Objective To determine if interferential current (IFC) or transcutaneous electric nerve stimulation (TENS) alters C and A delta fiber-mediated thermal perception thresholds. Design Single-blind, randomized controlled trial. Setting Laboratory. Participants One hundred forty healthy women volunteers (mean age ± standard deviation, 20.6±2.7y). Interventions Subjects were randomly and exclusively assigned to 1 of 7 groups (n=20 in each): 0, 5, and 100Hz of IFC; 5 and 100Hz of TENS; placebo and control stimulation. Stimulation was applied through 2 electrodes placed over the median nerve. Warm sensation, cold sensation, hot pain, and cold pain perception thresholds were measured from the thenar eminence by using a quantitative sensory testing device and a method of limits algorithm. Main outcome measures Warm sensation, cold sensation, hot pain, and cold pain thresholds (°C) before, during, and after stimulation. Results There was a statistically significant effect of time for all 4 thermal perception thresholds (separate 2-way analyses of variance with repeated measures, all P<.001). There were no statistically significant differences between experimental groups, nor any interaction effects (all P>.05). Conclusions Neither IFC nor TENS altered C and A delta fiber-mediated thermal perception thresholds. The results suggest that any analgesic mechanisms with these modalities are likely to be complex.