P302 Search for optimal protocol of temporal summation of experimental heat pain in healthy volunteers

QuestionExperimental human pain models are often insufficient to detect moderate effect of non-opioid analgesic drugs or hypoalgesic neuromodulation. Measurement of temporal summation of pain (TSP) is a promising tool for this purpose. The aim was to find out optimal stimulation parameters for a new protocol that consistently reproduces the TSP phenomenon.Material & methodsTwenty healthy volunteers (15 females) underwent 4 sessions with different stimulation parameters with an interval of at least 48h in-between. After determining the individual pain threshold temperature, pulsating heat stimuli were applied to the left ventral forearm with a ramp rate of 20°C/s and a frequency of 0.33Hz using a CHEPS thermode (Medoc, Israel). Stimulation temperature, pulse duration and number of stimuli were changed among the conditions I–IV (Table 1). Participants rated the perceived pain of the first and every 10th heat stimulation using a numeric rating scale 0–100. TSP was calculated as the difference between the lowest rating and the rating of the last stimulus and was compared among 4 conditions.ResultsCondition IV yielded the largest TSP effect (20±3.1; mean±SEM), which was higher than TSP effect of condition I (7.9±2.2; p=0.03) and II (6.8±1.5; p=0.012; Fig. 1). TSP effects of condition III and IV were comparable, however condition IV caused discomfort and intolerable pain in 9 participants; no one complained about discomfort during other conditions.ConclusionThe protocol with high number of repeated stimuli and short pulse duration (<1.0s) is feasible to reproduce TSP phenomenon. Heat stimulation with long pulse durations and high stimulation temperatures are not feasible in experimental human pain research.