Transcutaneous electrical nerve stimulation and transcutaneous spinal electroanalgesia: a preliminary efficacy and mechanisms-based investigation.

OBJECTIVES

To determine the effects of transcutaneous electrical nerve stimulation (TENS) and transcutaneous spinal electroanalgesia (TSE) on mechanical pain threshold (MPT) and vibration threshold (VT).

DESIGN

A prospective, single-blind, randomised, placebo-controlled trial.

SETTING

Laboratory based.

PARTICIPANTS

Thirty-four healthy volunteers (12 men and 22 women; mean age+/-standard deviation 30+/-8 years). Exclusion criteria were conditions affecting upper limb sensation and contraindications to electrical stimulation.

INTERVENTIONS

Participants were allocated at random to receive TENS (n=8), TSE (n=8), placebo (n=9) or control (n=9). Electrical stimulation was applied for 30 minutes (from time 18 minutes to 48 minutes) via electrodes (5 cmx5 cm) placed centrally above and below the space between the C6 and C7 spinous processes, with 5 cm between electrodes.

MAIN OUTCOME MEASURES

MPT (using an algometer) and VT (using a vibrameter) were recorded on seven occasions from the first dorsal interosseous muscle of the right hand - at baseline (0 minutes) and then at 10-minute intervals until the end of the 60-minute testing period.

RESULTS

There were no statistically significant group differences in MPT (all p>0.05). Significant group differences in VT were found at 20, 30 and 40 minutes (all p<0.05). Post-hoc tests showed that the TENS group had significantly greater VT than both the placebo [median difference 0.30 microm, 95% confidence interval (CI) -0.05 to 0.66] and control (0.51 microm, 95% CI 0.05 to 0.97) groups at 20 minutes, and significantly greater VT than the control group (0.69 microm, 95% CI 0.20 to 1.17) at 30 minutes (all p<0.008).

CONCLUSIONS

Electrical stimulation did not alter MPT. The increase in VT during TENS may be due to distraction or antidromic block of large-diameter nerve fibres. TSE failed to alter either outcome measure significantly.