Psychophysical responses to experimentally induced heat and cold pain before, during, and after transcutaneous electrical nerve stimulation.

Objective.  The outcomes of different modes of TENS (transcutaneous electrical nerve stimulation) in relieving experimental heat and cold pain were studied. Materials and methods.  Three modes of stimulation, conventional, burst, and high rate frequency modulation (HRFM) including placebo, were trancutaneously applied to 20 right handed healthy volunteers (10 males and 10 females). Stimulation was carried out using two pad electrodes placed over the median nerve for 120 s in each case. Heat pain was induced to the right and left hands of each subject by means of a hot water bath and cold pain by means of frozen bottles. Pain scores based on Verbal Rating Scale (VRS) were recorded at 60 s intervals before, during, and after stimulation. Results.  All stimulation modes except placebo decreased VRS values down to statistically significant levels in each case (p < 0.05). HRFM was the most effective mode of TENS causing a decrease of 53.1% to perception of heat pain during its application and 43.8% after HRFM in the right hand. In the left hand, these values were recorded as 46.8% and 40.3%, respectively. HRFM also decreased the perception of cold pain by 47.2% during stimulation and 44.5% after stimulation in the right hand. In the left hand, cold pain scores were reduced by 52.8% and 45.1%, respectively. There were no statistically significant sexual differences and no recorded statistically significant difference between the right or left sided stimulation. Conclusions.  All modes of stimulation statistically decreased both heat and cold pain when compared to placebo. HRFM was the most effective mode of TENS. It might be worthwhile to test the patterns of stimulation in chronic pain patients.