Physiological mechanism of depression from the view of changes in motor activity and R-R interval

Abstract

Depression is often accompanied with various physical symptoms, especially autonomic nervous system's symptoms such as dizziness when standing, palpitation and stiff shoulders. The object of this study is to estimate physiological state in depression objectively by measurement of motor activity and autonomic nervous system's activity using actigraphy. Seven depressed patients at a psychiatric ward in our university hospital who met the DSM-IV criteria for major depressive disorder, and who had a score of seventeen or higher on the 17-item Hamilton rating scale for Depression (Ham-D) before treatment were enrolled in this study. All patients participated this study voluntarily in agreement with its purport and written informed consent was obtained from them. This study was approved by the ethics committee of the University of Occupational and Environmental Health. All the seven patients were females and the mean age was 67.1±7.7years. The R-R interval and motor activity were measured simultaneously by an actigraphy over three days from the date of admission and recovery of depression. The clinical symptoms on each patient were also evaluated by using the Ham-D at the same time. Motor activity was significantly increased after recovery from depression. The HFnorm, which probably reflects the activity of cardiac vagal nerves, showed a trend of increase. On the other hand, LF/HF, which is the ratio of LF to HF and is thought to be a marker of sympathetic nervous activity decreased significantly after recovery from depression. These findings suggest the possibility that the activity of the sympathetic nerves would be higher and the activity of the vagal nerves system would be lower in depressive states. Furthermore the fractal dimension of the R-R interval power spectrum was decreased significantly lower after recovery from depression. It could be supposed that this fractal dimension has a close relationship to the balance of total autonomic nervous system activity. Therefore further study will be needed to elucidate these arguments.