<b>Measuring heat flux and amount of heat as indexes </b><b>of cold pain threshold </b>

Abstract

Background: Quantitative sensory testing (QST) has been widely promoted in the clinical and research domains. To date, however, measurements of heat flux (HF) and/or amount of heat (AH) as indexes of cold pain threshold in QST have not been reported. The purposes of this study were to measure HF and AH as indexes of cold pain thresholds and to examine the usefulness of this methodology for assessing cold pain threshold. Methods: We measured HF, AH and variation in skin temperature (VST) as indexes of the thermal perception threshold for cold pain stimuli using a thermal stimulator (Intercross-200). Thresholds were measured at the central region of the palm in 24 healthy volunteers from the approximate skin temperature of the subject at three different rates of temperature decrease (0.1, 0.3 and 0.5°C/sec). The intraclass correlation coefficient (ICC) was applied to investigate measurement repeatability. The Spearman's rank correlation coefficient was used to assess the relationship between premeasurement skin temperature and thresholds. The Spearman's rank correlation coefficient was also used to assess the relationship between VST and HF and between VST and AH. Results: ICC for thresholds were high (> 0.9) for all measurement conditions and parameters. Thresholds were not correlated with premeasurement skin temperature. AH was more correlated with VST than HF. AH assessed using a temperature decrease of 0.1°C/sec were significantly higher than those measured with temperature decrease of 0.3 and 0.5°C/sec. AH varied widely among individuals with the temperature changing at 0.1°C/sec. Conclusions: The results show that the Intercross-200 thermal stimulator and methodology employed in this study are useful for assessing cold pain threshold. Moreover, AH is applicable to the measurement of cold pain threshold at a temperature close to the skin temperature of a subject. Furthermore, temperature changes at rates of 0.3 and 0.5°C/sec are suitable for measurement of cold pain threshold.