Measurements of Temporal Summation of Heat Pain: a Pilot Investigation in Healthy Humans

Temporal summation of pain (TSP) is a promising tool for measuring the pain modulation processes in healthy subjects and patients with chronic pain. We tried to find optimal stimulation parameters in order to elicit a robust reproducible TSP phenomenon. Twenty healthy volunteers (15 women and 5 men) completed four sessions/conditions of pulsating heat pain stimulation, applied to the left forearm with a frequency of 0.33-0.4 sec(-1) using a contact heat-evoked potential stimulator. The stimulation temperature (step +0.5 degrees C or +1.0 degrees C up to the pain threshold, pain tolerance), pulse duration (500, 800, or 1000 msec), and number of stimuli (60 or 90) were varied. The participants rated the pain intensity at the first and every 10th heat pulse, using a numeric rating scale (NRS) 0-100. The TSP was calculated as the difference between the lowest rating and the rating of the last stimulus and was compared between conditions. The optimal condition (19 out of 20 participants responded with TSP) showed temperature at pain tolerance, pulse duration of 800 msec, and 90 stimuli. In addition, this condition showed weaker side effects (painful discomfort) than those with less (60) but longer (1000 msec) stimuli presented 1.0 degree above the pain threshold. The protocol with a relatively high stimulus repetition and a moderate pulse duration seems to be the optimal protocol to reproduce TSP. Heat stimulation with longer pulse durations and higher stimulation temperatures was less feasible.