The Effect of Rate of Temperature Change on Thermal Detection Thresholds in the Trigeminal Region

Objectives: Thermosensory testing is used to assess patients who have neurological abnormalities. The rate of temperature change influences the detection threshold, with rapid change resulting in a 'reaction time artefact' and higher thresholds, and so a standard rate of temperature change of 1^oC s^-1 is normally used. Low detection thresholds on the face suggest that a slower rate of temperature change would more accurately determine the threshold. This investigation has compared the effect of different rates of temperature change on thresholds on the face and hand of normal subjects. Methods: Warm detection thresholds (WDT) and cold detection thresholds (CDT) were determined in the mental region and in the thenar region at four rates of temperature change; 0.3^oC s^-1, 0.5^oC s^-1, 0.75^oC s^-1 and 1^oC s^-1, in thirty healthy adults. Tests were undertaken using a 256mm² peltier thermode (Medoc Thermosensory Analyser). Thresholds were measured by the method of limits, and the median threshold to five consecutive stimuli was determined. Statistical comparisons were made using ANOVA and Tukey's multiple comparisons. Results: The WDT on the hand at 1^oC s^-1 was 3.02±1.4(mean±SD)^oC but reduced by up to 0.57^oC (19%) with slower rates of temperature change. CDT on the hand was 1.62±0.6^oC at 1^oC s^-1 but reduced by up to 0.4^oC (25%) at slower rates. On the face the WDT was 1.18±0.8^oC at 1^oC s^-1 and reduced by up to 0.23^oC (19%) at slower rates. The CDT on the face was 0.63±0.3^oC at 1^oC s^-1 and reduced by up to 0.15^oC (23%) at slower rates. Conclusions: The results of this study confirm that thermal thresholds are reduced at lower rates of temperature change in both thenar and mental regions. However, the proportionate reduction in threshold at lower rates of change is similar in the two regions.