Cold and hot step-changes affecting thermal comfort and physiological indicators in winter

This study reported subjective and physiological responses to cold and hot winter step-changes, and explored the body's regulation mechanism. The step-change processes contained three high-temperature and one low-temperature — the air temperature in the high-temperature stage was set to 18/24/30 °C, and the temperature in the low-temperature stage was 15 °C. Therefore, I3, I9 and I15 were defined as “15–18–15 °C”, “15–24–15 °C” and “15–30–15 °C”. The thermal sensation vote (TSV) and thermal comfort vote (TCV) of 16 participants was investigated under three different step-changes, and the skin temperature, dopamine (DA), heart rate (HR) and blood oxygen saturation (SpO2) were measured. The statistical analysis shows that the TSV was asymmetric after cold and hot step-changes. The TSV and TCV stabilized in approximately 20 min, but the mean skin temperature (Tmean) took longer. The changes in the subjective and objective parameters before and after step-changes were calculated. We observed that ΔTmean, ΔHR and ΔSpO2 increased after hot step-changes, while cold step-changes had the opposite effect. Greater strength step-changes increased the burden on the body, resulting in health risks. In addition, subjective voting, Tmean, HR and SpO2 were significantly correlated. ΔDA was positively correlated with the temperature difference of the step-changes, and the |ΔDA| values of I3 and I15 were almost equal. The step-changes of I9, which included neutral temperatures of 24 °C, were more acceptable to participants, and the ΔDA, representing the degree of human pleasure, was smaller.