Reliability of the method of levels for determining cutaneous temperature sensitivity

During capsaicin-induced central sensitization, brush allodynia is associated with baseline warmth sensitivity, whereas mechanical hyperalgesia is associated with painful mechanical sensibility, anxiety and somatization

BACKGROUND

Mechanical hyperalgesia and allodynia incidence varies considerably amongst neuropathic pain patients. This study explored whether sensory or psychological factors associate with mechanical hyperalgesia and brush allodynia in a human experimental model.

METHODS

Sixty-six healthy volunteers (29 male) completed psychological questionnaires and participated in two quantitative sensory testing (QST) sessions. Warmth detection threshold (WDT), heat pain threshold (HPT) and suprathreshold mechanical pain (STMP) ratings were measured before exposure to a capsaicin-heat pain model (C-HP). After C-HP exposure, brush allodynia and STMP were measured in one session, whilst mechanical hyperalgesia was measured in another session.

RESULTS

WDT and HPT measured in sessions separated by 1 month demonstrated significant but moderate levels of reliability (WDT: ICC = 0.5, 95%CI [0.28, 0.77]; HPT: ICC = 0.62, 95%CI [0.40, 0.77]). Brush allodynia associated with lower WDT (z = -3.06, p = 0.002; ϕ = 0.27). Those with allodynia showed greater hyperalgesia intensity (F = 7.044, p = 0.010, η_p ²  = 0.107) and area (F = 9.319, p = 0.004, η_p ²  = 0.163) than those without allodynia. No psychological self-report measures were significantly different between allodynic and nonallodynic groups. Intensity of hyperalgesia in response to lighter mechanical stimuli was associated with lower HPT, higher STMP ratings and higher Pain Sensitivity Questionnaire scores at baseline. Hyperalgesia to heavier probe stimuli associated with state anxiety and to a lesser extent somatic awareness. Hyperalgesic area associated with lower baseline HPT and higher STMP ratings. Hyperalgesic area was not correlated with allodynic area across individuals.

CONCLUSIONS

These findings support research in neuropathic pain patients and human experimental models that peripheral sensory input and individual sensibility are related to development of mechanical allodynia and hyperalgesia during central sensitization, whilst psychological factors play a lesser role.

SIGNIFICANCE

We evaluated differential relationships of psychological and perceptual sensitivity to the development of capsaicin-induced mechanical allodynia and hyperalgesia. Fifty percent of healthy volunteers failed to develop mechanical allodynia. Baseline pain sensitivity was greater in those developing allodynia and was related to the magnitude and area of hyperalgesia. State psychological factors, whilst unrelated to allodynia, were related to mechanical hyperalgesia. This supports that the intensity of peripheral sensory input and individual sensibility are related to development of mechanical allodynia and hyperalgesia during central sensitization, whilst psychological factors play a lesser role.

Effect of material property, surface temperature and contact duration on the thermal sensation when contacting shell materials of electronic devices

Heat generated in electronic devices is generally unevenly distributed across the casing. Contacting the hot areas may cause thermal discomfort and possibly skin burn. This study aims at better understanding the interrelationship between the thermal sensation, material properties and surface temperature for enhancing the user experience of electronic devices. A Thermal Simulation System was developed in this study to precisely control the surface temperature of shell materials to simulate various end-use conditions. Seventeen participants were asked to contact the plates with their fingers and rate their thermal sensation using the magnitude estimation approach. Results showed that thermal sensation magnitude and plate temperature followed a power function. The differences in sensation magnitude can be attributed to the thermal inertias of different materials. The findings suggested that laminated plate was generally perceived cooler when heated. Given that the surface temperature of plate is higher than skin, the thermal sensation magnitude increases with contact duration.

Sex differences in thermal detection and thermal pain threshold and the thermal grill illusion: a psychophysical study in young volunteers

BACKGROUND

Sex-related differences in human thermal and pain sensitivity are the subject of controversial discussion. The goal of this study in a large number of subjects was to investigate sex differences in thermal and thermal pain perception and the thermal grill illusion (TGI) as a phenomenon reflecting crosstalk between the thermoreceptive and nociceptive systems. The thermal grill illusion is a sensation of strong, but not necessarily painful, heat often preceded by transient cold upon skin contact with spatially interlaced innocuous warm and cool stimuli.

METHODS

The TGI was studied in a group of 78 female and 58 male undergraduate students and was evoked by placing the palm of the right hand on the thermal grill (20/40 °C interleaved stimulus). Sex-related thermal perception was investigated by a retrospective analysis of thermal detection and thermal pain threshold data that had been measured in student laboratory courses over 5 years (776 female and 476 male undergraduate students) using the method of quantitative sensory testing (QST). To analyse correlations between thermal pain sensitivity and the TGI, thermal pain threshold and the TGI were determined in a group of 20 female and 20 male undergraduate students.

RESULTS

The TGI was more pronounced in females than males. Females were more sensitive with respect to thermal detection and thermal pain thresholds. Independent of sex, thermal detection thresholds were dependent on the baseline temperature with a specific progression of an optimum curve for cold detection threshold versus baseline temperature. The distribution of cold pain thresholds was multi-modal and sex-dependent. The more pronounced TGI in females correlated with higher cold sensitivity and cold pain sensitivity in females than in males.

CONCLUSIONS

Our finding that thermal detection threshold not only differs between the sexes but is also dependent on the baseline temperature reveals a complex processing of "cold" and "warm" inputs in thermal perception. The results of the TGI experiment support the assumption that sex differences in cold-related thermoreception are responsible for sex differences in the TGI.

Diurnal variation in the core interthreshold zone and its relation to cutaneous sensation threshold zone

BACKGROUND

The core interthreshold zone (CIZ) is defined as the range between temperatures at the onset of shivering and sweating. Its circadian or diurnal variation has not been extensively studied. The present study examined whether the CIZ is subject to a diurnal rhythm. In addition, according to the previous finding that the CIZ was proportionally correlated with peripheral interthreshold zone (PIZ), it was also examined whether cutaneous sensation threshold zone (CSZ), a determinant of the PIZ, is correlated with the CIZ.

METHODS

The CIZ and the CSZ were measured in ten Japanese men who underwent three experiments in a single day on the morning, afternoon, and evening in the 2014 experiment (so-called single-day experiment) and six Japanese men underwent the same experiments on the morning of day 1, the afternoon of day 2, and the evening of day 3 in the 2015 experiment (so-called multiple-day experiment). Air temperature was controlled at 20-24 °C. Each subject wore a suit perfused with 25 °C water at a rate of 600 cm³/min and exercised on an ergometer at 50% of their maximum work rate for 10-15 min until their rate of sweating increased. They then remained seated without exercising until their oxygen uptake increased. Rectal temperature, skin temperatures at seven sites, the sweating rate at the forehead, and oxygen uptake were continuously monitored throughout experiment. Cutaneous warm and cold sensation thresholds at three sites were measured using 1- and 2-cm² probes.

RESULTS

The results from the single-day experiment demonstrated a small change in the CIZ and core temperature prior to exercise (T _c-init) whereas those from the multiple-day experiment demonstrated continuous increase in the CIZ and T _c-init. The CSZ measured with a 1-cm² probe was inversely proportional to the average skin temperature at three sites prior to measurement (T _sk-av).

CONCLUSION

The results suggested that the CIZ may be not dependent on time of a day but T_c-init per se and may not be associated with the CSZ.