Evaluation of the cognitive performance of nuclear power plant operators using heart rate variability under hot-humid exposure

• Comparison of humidity 60 %, 70 %, 80 %, and 90 % on cognitive performance. • VLF could be a reliable indicator of cognitive performance in hot-humid exposure. • HRV indicators have a significant impact on cognitive performance. • The significant factors of HRV differ for different cognitive abilities. When sudden disasters such as earthquakes and tsunamis culminate in the outage of control systems in nuclear power plants, the operators may be exposed to extremely hot-humid environmental conditions while still facing demanding cognitive tasks. To investigate how their cognitive performance is related to their heart rate variability (HRV), we exposed nuclear power plant operators to four high temperature and humidity environments and measured their HRV during seven different cognitive tasks for 30 min. Generalized linear mixed-effects models (GLMMs) are used to analyze the relationship between HRV and operators' cognitive performance. Studies have shown that all indicators of HRV have a significant impact on the cognitive ability of operators. In both the low frequency (LF) and high frequency (HF), especially in the very low frequency (VLF) domain, HRV significantly correlates with the operator's cognition. Although the cognitive performance aggravates slightly within 30 min, increasing the humidity under fixed high temperatures does not exhibit an overall effect on cognitive performance. Henceforth, this study provides a guidance for safety limits of the operator's working duration. Moreover, VLF, LF, and HF domains might be potential physiological indicators to monitor the cognitive ability of operators.