EFFECT OF POSTURAL CHANGES ON BAROREFLEX SENSITIVITY: A study on the EUROBAVAR data set

摘要

The effect of changing posture from supine to standing on the heartrate variability (HRV) was analyzed on the EUROBAVAR data set using power spectral analysis. Power spectral analysis has been commonly used to provide indices of autonomic cardiovascular modulation. Although the interpretation of power spectra is in dispute, it is generally agreed that the high-frequency (HF) power components represent the cardiac vagal modulation and the low-frequency (LF) power components are related to sympathetic activity. And then their ratio (LF/HF) is considered as an index of sympathovagal balance. In the supine lying position, relatively fast vagal activity plays a dominant role, whereas the upright standing position results in vagal inhibition and sympathetic predominance. Postural changing from supine to standing position showed the significant decrease in the indexes of vagal influence on HRV; HF power in both absolute and normalized unit decreased (320 to 121 ms~(2) X 10~(3)/Hz with P < 0.005 and 49 to 37 n.u. with P < 0.005, respectively) and LF/HF increased (1.4 to 2.65, P < 0.005). The baroreflex sensitivity (BRS) values were estimated by time sequence method, alpha-coefficients and transfer gains in LF and HF bands. There was a clear difference between BRS values in the supine and the standing positions with the averaged supine-to-standing BRS ratios of 2.35 +- 0.4. BRS estimates using HF components indicated higher values than LF analysis. With the evident decrease in normalized HF power and increase in LF/HF, the effect of changing positions to standing from supine lying can be concluded as a clear reduction in vagal influence on the heart rate variability.