Study the Effect of Cognitive Stress on HRV Signal Using 3D Phase Space Plot in Spherical Coordinate System

In this article, the effect of stress on heart rate variability (HRV) is analysed, while a human mind is subjected to different stressful situations. The subjects had to go through a series of challenges that exaggerate their mental stress. The subjects had been given specific tasks which are both time bound and without any limitation of time. The HRV signals are taken before and after the completion of tasks. The quantification is done by fitting an ellipse on the constructed a 2D phase space of the HRV signal. But the 2D phase space plot is not able to distinguish HRV signals on normal and stressful conditions for all the time. In this paper, we introduce a 3D phase space plot in a spherical coordinate system which can distinguish normal and stressed conditions significantly. It has been observed that the volume of the cluster in reconstructed space increased drastically on stressed condition. The volume of the fitted ellipsoid on the reconstructed space is a proper quantification tool which can clearly distinguish two aforesaid conditions. Our experimental result provides a satisfactory result in this context.