Potential indicators for the effect of temperature steps on human health and thermal comfort

• Sensitive physiological and biochemical indicators corresponding to temperature steps were found.
• Skin temperature, RMSSD and LF/HF are more sensitive to temperature down-steps.
• Relationship between subjective perceptions and physiological parameters was discussed.

This study explored human physiological and biochemical responses to temperature steps. Experiments with three step-change conditions (S5: 32 °C-37 °C-32 °C, S11: 26 °C-37 °C-26 °C, and S15: 22 °C-37 °C-22 °C) were conducted with 24 volunteered participants. Various biomarkers and physiological parameters, reflecting functions of immune system (serum level of IL-6 and HSP70), thermal metabolism system (oral temperature and skin temperature), respiratory system (RR and SPO2) and cardiovascular system (HR and HRV measures), were recorded. The statistical analysis shows that IL-6, oral temperature, skin temperature, HR and HRV are sensitive to temperature step changes. Moreover, both temperature step intensity and direction have significant impacts on human physiological parameters. Human responses of skin temperature and HRV (RMSSD and LF/HF) are significantly more sensitive to temperature down steps, indicating that the risk of down-step may be more serious than that of its up-step counterpart. In addition, significant relations were observed between subjective perceptions and physiological parameters with the method of canonical correlation analysis.