Günther Galfe

Diurnal variations in pain perception and thermal sensitivity

&NA; Pain and thermal sensitivity thresholds in healthy volunteers were examined for diurnal variations. The subjects were 11 men aged between 22 and 27 years (x = 23.5, S.D. = 1.5). Data were collected for 2 days, with 7 measurements per day. To ensure the pain specificity of the results the subliminal modality i.e., thermal sensitivity thresholds to warm and cold stimuli, was investigated in addition to the threshold for perception of heat pain. Assessments were made on the right hand and foot, the stimuli being presented with a thermoelectric contact‐thermode. Despite the influence of variables other than time of day (45–56% of the total variance), diurnal variations were found for some subjects on the pain threshold measure (significant correlation between days and relatively high frequency of 24 h component in Fourier analysis spectra). However, they could not be demonstrated for the thermal sensitivity measures. The diurnal variations in pain perception thresholds did not have a consistent pattern over all subjects (Friedman test). The small diurnal variations with interindividual differences in the pattern are therefore not sufficient to explain the variations seen in clinical pain, but they may be useful in detecting pain modulators by investigating correlations.

Effects of chronic back pain on the perception of experimental heat pain

19 patients between 23 and 65 yr. of age whose chronic back pain was caused by lumbosacral disk disease and 19 healthy volunteers matched for age and sex were studied. Pain thresholds under phasic and tonic heat stimulation and thermal thresholds for warmth and cold were measured on the right hand. The patients rated any current back pain on a visual analog scale. There was a significant negative correlation between current back pain and the threshold for tonic pain, but there was no correlation between current back pain and either the threshold for phasic pain or temperature sensitivity. Hence, current back pain and experimental tonic pain seem to have an additive effect on pain perception because perceptual qualities are similar. Reduced somatosensory perception of chronic back pain patients could be demonstrated for temperature sensitivity and to a lesser degree for phasic pain, but as a consequence of the “opposing” effect of current back pain, not for tonic pain perception.

Disturbances of C-fibre-mediated sensibility in lumbosacral disc disease.

In nine patients with chronic lumbosacral disc disease and radicular symptoms clearly restricted to one leg, C-fibre-mediated sensibility was measured by determination of the thresholds for heat pain and warmth on the foot, ipsi- and contralaterally to the nerve root compression. The thresholds were compared with the values for 19 healthy subjects. In the patients the warmth threshold was increased in the ipsilateral dermatome and normal in the contralateral dermatome. In contrast, the heat pain threshold was near normal ipsilaterally but was clearly decreased contralaterally. These findings are discussed with respect to a possible pain sensitisation resulting from nerve root compression.

SDT Analysis of Experimental Thermal Pain, with “Signal” and “No-Signal” Being Determined Psychophysically

In a signal-detection experiment, the effects of repeated pain stimulation and the induction of fear on pain thresholds and SDT parameters were studied. “Signal” and “no-signal” were not defined physically, but by means of an independent criterion as the primary sensations “pain” and “no-pain.” First, the relationship between sensation levels for “phasic” (short stimulus, used in the SDT procedure) and “tonic” (longer stimulus, used in the criterion measurement) heat stimuli was determined in 14 subjects. It was quadratic (polynomial regression) and sufficient to define the distinction between “signal/pain” and “no-signal/no-pain.” In the signal-detection experiment, a significant upward trend (adaptation) in threshold parameters, but no systematic change in the SDT parameters (discrimination ability and response bias) was found. Manipulation of anxiety by instructions caused unsystematic changes in discrimination ability. The procedure employed determines both the absolute strength of pain sensation and the ability to discriminate pain from no pain. These variables proved to be independent.

Threshold Tracking for Assessment of Long-Term Adaptation and Sensitization in Pain Perception:

To assess temporal variations in the perception of “phasic” heat pain stimuli a psychophysical tracking procedure was developed that enables repeated assessment of the pain threshold at short intervals. This “double-tracking” procedure produces two tracking curves simultaneously, one that approaches the pain threshold gradually from above, the other from below. The threshold for phasic heat pain was measured in 80 tracking trials with stimuli at temperatures near the pain threshold. Concurrently, the threshold for “tonic” heat pain was determined after every 20 tracking trials with a stimulus adjustment procedure. Eleven healthy subjects (age: 26.4 yr. ± 6.0) participated in 2 sessions each. Phasic stimulation near the pain threshold did not produce any trends in either of the two threshold measures. Hence there was no long-term adaptation or sensitization. However, there were random variations (random walks) in the tracking curves, which we interpret as resulting from a stochastic relationship between stimulus and sensation. In agreement with other reports, discrimination seemed to be better at painful than at nonpainful temperatures.