Physiological and subjective thermal responses to heat exposure in northern and southern Chinese people

Abstract

When studying the thermal adaptation of building occupants, understanding the effects of different thermal experiences on adaptation is necessary, particularly for moderate and severe heat exposure. However, this area has seen limited research. Further, skin temperature, a common parameter for quantifying thermal sensation, may insufficiently reflect the automatic thermoregulation of the human body. This study investigates the effects of long-term heat exposure on the human body using multiple physiological and subjective indexes. Two heat exposure experiments were conducted on healthy male participants from northern and southern China. Participant responses, including skin temperature, heart rate, heart rate variability, blood volume pulse (BVP), subjective thermal comfort, thermal sensation, thermal acceptability, and normalized high and low frequency values were collected and compared. The results indicated that the subjective responses of northern and southern participants were not significantly different; however, the subjective physiological symptoms and self-reported discomfort of the latter were less than those of the former, indicating that the southern participants had superior heat tolerance. Additionally, the physiological responses of all the participants were largely similar. However, southern participants showed slightly higher normalized high frequency and BVP values, indicating that they have more active vagus nerves and better vasodilation. They also showed a wider acceptable temperature range and better acclimation to heat exposure. Notably, the mean skin temperature could not effectively predict thermal sensation during heat exposure; this was more accurately achieved using the rate of change of skin temperature. These findings suggest that long-term thermal experiences can affect building occupants’ thermal adaptability.