Evaluation of human attention during sustained heat exposure using typical thermoregulation-related indices

Abstract

Heatwaves can usually lead to severe attentional decline. However, the effect of heatwaves has not been sufficiently evaluated quantitatively, particularly through some easily acquired thermoregulation-related indices. To address this issue, 14 participants were exposed to various temperatures of 22 °C, 31 °C, 33 °C and 35 °C, under 55% relative humidity, over a 150-min duration. The air temperature of 22 °C was used as a control condition. Four attentional tasks were administered at each environmental temperature. During the experiment, mean skin temperature (MST), core temperature, heart rate (HR) and cortisol were measured. Results showed that the attentional performance was reduced under 31 °C, 33 °C and 35 °C (p < 0.05). The mean HR was reduced over the exposure time under all temperatures (p < 0.001) but rose significantly with air temperature (p < 0.05). Meanwhile, MST was increased significantly by the air temperature (p < 0.001) under 31 °C, 33 °C and 35 °C, over the exposure duration. However, MST was reduced significantly over the exposure time under 22 °C (p < 0.05). Furthermore, cortisol concentration varied significantly with air temperature (p < 0.05). Correlation analysis indicated that the attentional performance was negatively correlated with MST, with a Spearman's ρ of −0.58 (p < 0.05), based on which, a quantitative relationship for the evaluation of attention was proposed using R² of 0.69 (p < 0.05).