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

Abstract

BackgroundThe 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.MethodsThe 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.ResultsThe 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).ConclusionThe results suggested that the CIZ may be not dependent on time of a day but Tc-init per se and may not be associated with the CSZ.

Diurnal Variation in the Core Interthreshold Zone in Women and its Sex Difference

“…The reason may be due to a difference in mean skin temperature, because was kept low at 28-30°C in the present study using a water-perfused suit, as opposed to the studies by Anderson et al 9 and Lopez et al 10 where the was maintained higher at 35-36°C. Considering the standard T c diurnal rhythm, which is a progressive increase in T c in the morning, followed by a more gradual increase during the afternoon and then a relatively constant T c during the evening, the CIZ in the morning is likely the narrowest CIZ of the day, which then widens during the afternoon and evening, as demonstrated in the previous study of men 7 .…”

“…Because the effect of lighting and season on the CIZ was confirmed in a previous study 5 , luminance was carefully controlled at 1,000 lx, and all experiments were conducted from August to September, as described in the experimental protocol of our previous study 7 .…”

“…In a previous study [7], a series of experiments for male subjects was carried out in 2014 and 2015 using the same experimental protocol. , cutaneous temperature sensitivity can be compared under various thermal conditions, as long as it was measured at a constant rate change of 1 °C/s.…”

“…This finding suggested that diurnal variation in the CIZ could be correlated with the cutaneous sensation threshold zone (CSZ), a determinant of the PIZ. In a series of CIZ studies carried out from 2014 to 2015, diurnal changes in the CIZ for Japanese male subjects were investigated by measurement of the CSZ using a thermal simulator 7 .…”