Quantitative Evaluation of Effects of Visually-Induced Motion Sickness Based on Causal Coherence Functions between Blood Pressure and Heart Rate

To evaluate the effect of VIMS, the present study has analyzed the linearity of the baroreflex system and that of the mechanical hemodynamic system by using causal coherence functions. The causal coherence functions have a capability of calculating linear correlation between two systems independently even if the systems are connected with each other to compose a closed-loop system. In the experiment, 56 healthy human subjects' heart rate and continuous blood pressure variability were measured to obtain the causal coherence functions when they were watching an unstable video image. The results showed that there were significant differences in the causal coherence functions as well as the traditional coherence function between the subjects who felt VIMS and those who did not, and that the hemodynamic system was mainly disturbed by VIMS rather than the baroreflex system. These findings suggest that the causal coherence functions of the two systems and the traditional coherence function of the whole system gave different information from one another. This fact implies that the causal coherence functions will be useful and can be objective means to quantify VIMS.