Evaluation of the cognitive performance under hot-humid environments using heart rate variability

Abstract

The human cognitive performance under hot and humid exposure is a critical issue for people working under hot and humid environments, for the considerations of both their health and safety. In order to find an indicator of the cognitive performance, the electrocardiogram (ECG) data were recorded continuously for 2.5 hours with portable Holter, when participants were exposed to 4 hot-humid environmental conditions and conducting different cognitive tests. The ECG data then were analysed to obtain the HRV indices that were used to establish a relationship with the cognitive test results. Temporal index pNN50 of HRV time domain indices was selected as a biomarker of the cognitive performance in this study. Results showed that the pNN50 responded significantly to the air temperature, while the influences of the cognitive tasks and the exposure time were found to be less significant. Meanwhile, the mean accuracy of the cognitive tasks was found to be positively related to the changes of mean pNN50, but a negatively related relationship between the mean reaction time and the mean pNN50 was observed. Furthermore, a positive relationship between the relative cognitive performance and the pNN50 was obtained, which meant that higher pNN50 responded to the higher cognitive performance. The potential reason could be ascribed to the changes in temperature-related allocation of the mental resources. And the low cognitive performance could be attributed to the rise of the mental fatigue due to the high sympathetic activities that corresponded to the low pNN50. The results revealed that the pNN50 could act as a biomarker of the cognitive performance under hot-humid exposure. The findings gave some implications to the real-time evaluation of the working performance and health of the people working under hot-humid environments.