Physiological evaluation of the cognitive performance under sustained hot-humid exposure

The global warming has been bringing a few extreme climate events in recent years, among which the heat wave happens more frequently and is accompanied by the high air temperature and humidity, producing more and more health issues, both physiologically and mentally (such as cognitive deficits). In order to explore the human cognitive changes under sustained hot-humid exposures, 14 right-handed male subjects were recruited and exposed to 4 different hot-humid environments for 150 min, during which 5 different cognitive tasks were administrated and the electrocardiogram (ECG) data were continuously collected. Thereafter, the time-domain analysis of heart rate variability (HRV) was performed based on the ECG data, to explore the correlations between time-domain indices (STDNN, pNN50, RMSSD) and the cognitive performance. Results showed that all time domain indices reduced significantly with the air temperature, and a certain relation was observed between the HRV indices and the exposure time. In addition, the correlation analysis results showed that the time domain index RMSSD was positively correlated with the cognitive performance (correlation efficient = 0.58, p<0.05) significantly. Subsequently, the quantitative relationship between RMSSD and the cognitive performance was obtained. Specifically, the cognitive performance reduced significantly when RMSSD was less than 20. When RMSSD was between 20 and 45, however, the cognitive performance reduced more slightly. This study showed that the HRV time-domain index RMSSD could act as a physiological indicator of the cognitive performance of people exposed to the hot-humid environment, thus could provide a potential solution for the ergonomics and health evaluation of people working in the heat.