Abstract
In order to investigate the relationship between changes in blood pressure and autonomic nerve activity during sitting positions, a graded sitting-position experiment was conducted. In the experiment, a graded bed up (0°, 30°, and 60°) of the upper body was performed. The electrocardiogram (ECG) and the blood pressure (JFNTOW) of 13 healthy subjects were recorded with the aid of the PowerLab System (PowerLab/8sp ; ADInstruments, Power Mackintosh 7200/90 ; Apple Computer), The systolic blood pressure at 60° poison showed a significant decrease as compared with the counterparts at the 0° and 30° positions (p < 0.005 and p < 0.01, respectively). No significant differences in the diastolic blood pressure were observed though the tendency of a decrease was exhibited as the angle load increased. The mean blood pressure at the 60° bed rise decreased as compared with the 0° position (p < 0.01). The areal ratio of the low-frequency power spectral component (LF) to the high-frequency one (HF), LF/HF, which is considered to serve as an index of the sympathetic nerve activity, significantly increased at the 60° position as compared with the 0° position (p < 0.05). On the other hand, the ratio of HF to the total area (TO), HF/TO, which is considered to serve as an index of the parasympathetic nerve activity, significantly decreased at the 60° position as compared with the 0° position (p < 0.0001). From these results, it was suggested that the spectral analysis of heart-rate variability can provide a non-invasive method for the evaluation of the autonomous adjustment.
