Evaluating responses of circulatory systems, sweating and pupil diameter to postural change

The autonomic nervous system (ANS) activity has been considered as an effective measure of the mental load increasing in modern information society. The heart rate variability (HRV) are commonly used to evaluate the balance between the sympathetic and parasympathetic activities. However, HRV can also be influenced by non-autonomic contributions such as blood flow. Moreover, the nonlinear interaction between the sympathetic and parasympathetic activities affect the HRV and thus they might not be clearly distinguished solely by the heart rate measurements. Therefore, more accurate evaluation requires investigation on co-variation across the indices of the ANS activities not only the HRV but also the ones which are not influenced by the change in blood flow and which are innervated by the sympathetic and parasympathetic branches in distinct ways. In this study, under the stimulation of postural change, three indices of the ANS activities; cardiovascular activity, sweat, and pupil diameter are measured simultaneously and evaluated. This experiment reveals high correlations between posture angle and each indices, and there is significant difference between correlations of RRI (R-R interval) and pupil diameter and between changes in RRI and sweat in supine position. These difference suggests difference between effects of sympathetic and parasympathetic activities.