<b>Examination of subjective sensations and vasomotor reaction to environmental temperature changes in </b><b>chronic pain patients with impaired cold sensation </b>

Abstract

Symptoms of pain in chronic pain patients are known to influence by ambient temperature (AT) change and some of these patients also show temperature unadaptability. These clinical features suggest that alteration of autonomic thermoregulatory systems might be underlying in development and maintenance of chronic pain. In this study, we examined effects of AT change exposure to the pain intensity and autonomic thermoregulatory function in chronic pain patients with impaired cold sensitivity. Two upper extremity neuropathic pain patients who have impaired cold sensitivity in whole body were participated in the present study. The subject sat a chair in an artificial climate chamber (27°C, 50% RH) during the experiment. After the baseline measurements, room temperature was decreased to 15°C in 25 min (cold exposure) and then increased to 40°C in 15 - 20 min (heat exposure). Pain intensity and thermal sensation (cold-cool-warm-hot feeling) during the exposure were frequently measured on a numerical rating scale. Skin temperature, skin blood flow (SBF), and sweating in both hands, and tympanic temperature were also measured continuously throughout the experimental period. In one patient, SBF showed lower baseline value in the affected limb than the healthy limb. During cold exposure, both patients showed increase in their pain intensity in the affected limb, but not expressed any cold feeling in spite of lowering tympanic temperature. Cold exposure decreased SBF in both hands of patients. During heat exposure, both patients expressed hot feeling as an ambient temperature gradually rises, but did not show any change in pain intensity. Heat exposure increased sweating, SBF in both hands of patients. The present study indicated that lowering ambient temperature increased pain intensity in the affected limb of two patients irrespective of impaired cold sensitivity. In these subjects, however, SBF and sweating responded in a different manner to the ambient temperature changes. This could reflect differences in autonomic thermoregulatory function between these patients.