Visualization of short-term HRV as an index for mental stress evaluation

This paper proposes a new method for visualization of the Heart Rate Variability (HRV) as a visual presentation for mental stress evaluation using the Symmetrized Dot Patterns (SDP) presentation. With this method, time series of the R-R intervals of the electrocardiogram (ECG) are mapped into a polar space and plot out as a scatter plot on the polar graph. The proposed method is testified with the ECG data of fourteen subjects during the mental work-load experiments. Mental arithmetic tasks were used for applying mental work load to the subjects. Experimental results show significant difference of the SDP of the R-R intervals between the mental workload phase and the rest phase, and the difference can be easily recognized. This fact verifies that the proposed method can serve as a visual presentation for the real-time evaluation of mental stress.