Quantitative sensory testing

Quantitative thermal perception testing in adults

In 225 adults aged 18 to 80 years, normative warm and cold perception thresholds were assessed at the volar distal forearm, thenar eminence, lower medial calf, and lateral dorsal foot using the method of limits and a Thermotest (Somedic, Stockholm, Sweden). A 1.5-cm x 2.5-cm thermode, a 1 degrees C/s stimulus change rate, and a 32 degrees C baseline temperature were applied. Thresholds of five consecutive stimuli were averaged. At the thenar eminence a 3 degrees C/s stimulation was applied in addition to the 1 degree C/s stimulation. Effects of spatial summation were studied at the calf and forearm by additional testing with a 2.5-cm x 5.0-cm thermode. To evaluate the influence of skin temperature, thresholds were correlated with the pretest skin temperature at the tested sites. Reproducibility of stimulus perception was determined by comparing the lowest to the highest response to five consecutive stimuli. Results showed sufficient accuracy of thermal perception thresholds. Thresholds were higher with the 3 degrees C/s stimulation than with the 1 degree C/s stimulation. Thresholds were lower with the large than with the small probe. Skin temperature had only minimal influence on thresholds. The use of a 32 degrees C baseline temperature and a 1 degree C/s stimulus change rate is recommended. The large probe should be used at body sites where the entire thermode surface adjusts planely to the skin. Warming up the tested skin area is not necessary before thermotesting.

Paradoxical heat sensation in healthy subjects: peripherally conducted by A delta or C fibres?

Paradoxical heat sensation upon cooling of the skin has been reported in central as well as in peripheral neurological conditions. In our study, we examined this phenomenon in 35 naive healthy test subjects, of whom 23 experienced paradoxical heat sensation under test conditions. We measured the peripheral conduction velocities of cold sensation, warm sensation and of paradoxical heat sensation by using a quantitative sensory testing model of indirect peripheral conduction velocity measurement. This was based on comparison of measurements at a proximal and a distal site using two measurement methods, one inclusive and the other exclusive of reaction time. We found that the conduction velocity of paradoxical heat sensation (0.70 m/s) was similar to that of warm sensation (0.68 m/s), and that the conduction velocity of cold sensation (7.74-8.01 m/s) was considerably faster. Thus, we conclude that paradoxical heat sensation in healthy subjects is conducted peripherally via slow unmyelinated C fibres and not via the faster A delta fibres. Consequently, we propose that paradoxical heat sensation is encoded via the heat sensing pathway, in accordance with the labelled-line code theory. The mechanisms proposed suggest a malfunctioning cold-sensing pathway disinhibiting the heat-sensing pathway, at peripheral, central or both levels, thus facilitating a paradoxical heat sensation.

Reliability of cephalic thermal thresholds in healthy subjects

Reproducibility and normal variation of cephalic warm and cold detection thresholds were investigated in three healthy subject groups. The face, the mastoid process, and the hands were studied. No significant intra-observer test-retest difference (n = 20) was found. Good reliability (intra-class correlation coefficient [ICC] > 0.4) was found for 13 of 14 measurements. A small significant inter-observer difference (n = 20) was found for cold thresholds. Good reliability (ICC > 0.4) was observed for both cold and warm thresholds in most of the test locations (6 of 8). In general, the largest variability was found in the mastoid and frontal lateral regions. Thermal thresholds varied with investigation site in 56 controls (ANOVA, p < 0.0005). No significant gender differences were found for cephalic warm and cold thresholds. Most cold thresholds (4 of 5) but also some warm thresholds (2 of 5) increased with age at the cephalic sites. Our results reveal the frontal medial, the maxillar medial, and lateral regions as the most reliable cephalic test locations. The mastoid region may also be useful for investigating the upper cervical small-fiber function.

Using electrical noise to enhance the ability of humans to detect subthreshold mechanical cutaneous stimuli

Stochastic resonance (SR) is a phenomenon wherein the response of a nonlinear system to a weak input signal is optimized by the presence of a particular, nonzero level of noise. Our objective was to demonstrate cross-modality SR in human sensory perception. Specifically, we were interested in testing the hypothesis that the ability of an individual to detect a subthreshold mechanical cutaneous stimulus can be significantly enhanced by introducing a particular level of electrical noise. Psychophysical experiments were performed on 11 healthy subjects. The protocol consisted of the presentation of: (a) a subthreshold mechanical stimulus plus electrical noise, or (b) no mechanical stimulus plus electrical noise. The intensity of the electrical noise was varied between trials. Each subject's ability to identify correctly the presence of the mechanical stimulus was determined as a function of the noise intensity. In 9 of the 11 subjects, the introduction of a particular level of electrical noise significantly enhanced the subject's ability to detect the subthreshold mechanical cutaneous stimulus. In 2 of the 11 subjects, the introduction of electrical noise did not significantly change the subject's ability to detect the mechanical stimulus. These findings indicate that input electrical noise can serve as a negative masker for subthreshold mechanical tactile stimuli, i.e., electrical noise can increase the detectability of weak mechanical signals. Thus, for SR-type effects to be observed in human sensory perception, the noise and stimulus need not be of the same modality. From a bioengineering and clinical standpoint, this work suggests that an electrical noise-based technique could be used to improve tactile sensation in humans when the mechanical stimulus is around or below threshold. (c) 1998 American Institute of Physics.

Normal distributions of thermal and vibration sensory thresholds

The distributions of sensory thresholds were estimated in a healthy population while controlling for potential covariates. Using the method of levels and the two-alternative forced choice, thermal and vibration thresholds respectively were measured in the hand and foot of 148 subjects. Age was uniformly distributed between 20 and 86 years. Independent effects of age, gender, height, and skin temperature were estimated using multiple linear regression. Parametric and nonparametric methods were used to estimate the distributions of interest. Significant age-related increases were observed for all vibration thresholds (P < 0.0001), and for thermal thresholds in the foot (P < 0.0002). Percentiles were estimated for thermal thresholds in the hand and age-adjusted continuous distributions were calculated for all other thresholds. Height was positively associated with vibration thresholds in the foot (P < 0.003), and appropriate corrections were made. Our results provide reference values for thermal and vibration sensory thresholds in a healthy population, allowing for the accurate diagnosis of disordered sensory function.

Clinical applications of quantitative sensory testing (QST)

Quantitative sensory testing (QST) has been used clinically for the last two decades, yielding a substantial number of publications regarding these applications. In this review we tried to amass together the major findings of these publications into one monograph, excluding those dealing with pain. This was done with the aim of assisting clinicians in the better use of QST techniques for the benefit of their patients.

Heat pain thresholds: normative data and repeatability

Measurement of thresholds for heat-induced pain was performed on 106 normal subjects, at thenar eminence and foot dorsum, using the reaction time-inclusive method of limits. Tests were repeated 2 weeks following the first test for most of the subjects. After determination that there were no outlying data points and that there was no systematic relationship between magnitude and variability of test scores, data from between 72 and 76 subjects were used to define normal upper and lower ranges by age, as well as repeatability coefficients. This was done through ANOVA-based procedures that extend standard repeatability assessment methods. Normative data tables are presented, with measures of repeatability for the various sites and modalities. For the conventional test range, reaching 55 degrees C, measurement of heat pain thresholds can define both hyper- and hypoalgesia. Application of repeatability coefficients allows for intra-individual inter-session comparison in longitudinal studies.