A STANDARD TEST OF HEAT-PAIN RESPONSES USING CASE-IV

Heat-pain threshold and stimulus response characteristics can be evalu ated with graduated heating pulses from a radiant heat source or a con tact thermode. Results may be used to: (1) evaluate differences in sen sation among anatomical sites, sides of the body, and with development and aging; and (2) provide an end-point for the study of the efficacy of drugs; or to follow the course of sensory alteration in disease (m edical practice, epidemiologic studies, and controlled clinical trials ). Because there is great variability in how tests of this kind are pe rformed and scored, comparisons of results among medical centers are d ifficult. To meet this need, we have developed, and here describe, a s tandardized and validated test of heat-pain. We use both pyramidal and trapezoid-shaped stimuli, The range of stimulus magnitudes we recomme nd is sufficient to test heat-pain at a sensitive region (the face) of young people and an insensitive region (the foot) of healthy old peop le, From tests on healthy subjects and patients, we find that neither our previously published forced-choice or 4, 2, and 1 stepping algorit hms are suitable for testing heat-pain sensation. We, therefore, intro duce the Non-Repeating Ascending with Null Stimuli (NRA-NS) algorithm which performs satisfactorily, The graphed data points of responses to increasingly stronger heat pulses were made up of two components-the no pain (0) response line and the heat-pain response line (greater tha n or equal to 1 numerical scaling of the pain responses graded from 1 [least] to 10 [greatest]). For the pain responses, we found that usual ly a curve could be fit using a quadratic equation. Using this equatio n, or interpolation where necessary, it is possible to compute the hea t-pain detection threshold (HPDT or HP:0.5), an intermediate heat-pain response (Hf:5.0), and the difference between the two (HP:5.0-0.5). O ur studies show that a certain time is needed between successive stimu li and tests to minimize changing basal skin temperature or threshold. We also demonstrated that low or high baseline skin temperatures can affect heat-pain responses, therefore, we advocate specific testing co nditions. Based on a study of 25 healthy subjects, the reproducibility of the test falls within +/- 1 stimulus steps 88% of the time for HP: 5.0 and 76% of the time for HP:0.5. The precise approaches employed to make the test standard and reproducible are described. We illustrate that the algorithm and testing system is able to document altered pain threshold with skin abrasion, with intradermal injection of nerve gro wth factor, and with diabetic polyneuropathy.