Increase of the heat pain threshold during and after high-frequency transcutaneous peripheral nerve stimulation in a group of normal subjects.

AIM: Transcutaneous electrical nerve stimulation (TENS) is used worldwide for pain relief, but its mechanisms of action are not completely understood. High frequency transcutaneous peripheral nerve stimulation (HF-TPNS) is a term describing a type of TENS where a peripheral nerve is stimulated transcutaneously. The aim of the investigation was to verify the hypothesis that HF-TPNS increases the heat pain threshold in the skin territory of the stimulated nerve, during and after stimulation.
METHODS: Eighteen volunteers (8 men, 10 women) participated in 2 sessions conducted on different days. In each session their heat pain thresholds were measured in basal conditions and after 5, 10, 15, 25, 40, 70 min. In one session, HF-TPNS was delivered for 10 min immediately after basal evaluation (HF-TPNS session). In the other session the heat pain thresholds only were measured (control session). The superficial radial nerve was stimulated at the wrist (frequency of 100 Hz, pulse duration of 0.1 ms). The heat pain threshold was studied using a contact thermode (surface of 12.5 cm(2)) placed in the cutaneous area of the stimulated nerve at the site where the paresthesia evoked by electrical stimulation could be felt.
RESULTS: HF-TPNS significantly increased the heat pain threshold both during and after stimulation.
CONCLUSION: This study confirms that HF-TPNS induces an important hypoalgesic effect. The prolonged duration of poststimulation hypoalgesia (60 min) indicates that continuous stimulation is probably unnecessary. Further studies are needed to test the hypothesis that intermittent HF-TPNS is able to maintain its hypoalgesic effectiveness over time.