Effect of thermode application pressure on thermal threshold detection

Abstract

Studies using quantitative sensory testing (QST) often present incongruent results due to intra- and intersubject as well as interobserver variability which limit widespread use of the technique. Eliminating or reducing the factors responsible for this variability is of great interest, as it increases reliability and reproducibility of QST. Thermal sensory threshold determination is a crucial part of QST. It was previously suggested that the pressure of the thermode on the skin could influence measurements. To verify this, we developed a new thermode with a built-in pressure sensor. Thresholds obtained with this thermode were compared to those obtained with a commercially available thermotesting device (Medoc TSA-II). Heat detection and heat pain detection thresholds were higher, and cold detection thresholds were lower when measured with our thermode than they were with the Medoc thermode. Cold pain detection thresholds did not differ between the thermodes. Analysis of the heat transfer capacity of the thermodes indicated that the material of the skin contact surface of the thermode may play a role in these shifts in threshold values. Altering the thermode pressure on the skin did not affect the thermal thresholds. Furthermore, the intrasubject variability of the measurements (minimal-to-maximal range of measured threshold values in individual subjects) was also not influenced by the pressure with which the thermode was attached to the skin. Our results suggest that the pressure with which the thermode is attached to the skin does not significantly affect the intra- and intersubject reproducibility of the thermal sensory threshold measurements.