Autonomic alteration in hypertension as unmasked by a change of posture and investigated by a time-frequency analysis of HR and BP fluctuations

The autonomic changes provoked by a change in posture (CP) among mild-hypertensive (H) and normal (N) adults were investigated by analysis of HRV and BPV. The non-stationary heart rate (HR) and blood pressure (BP) signals obtained during CP were submitted to our algorithm for time-dependent spectral analysis, the Selective DFT Algorithm (SDA). We observed a marked difference between the two groups in the low frequency component of BP fluctuations, at baseline (higher among H) and in the initial response to CP (damped in H). No significant difference was found in the spectrum of HR fluctuations. We conclude that the baseline enhanced BP fluctuations most probably reflect a basic /spl alpha/-sympathetic over-activity among H subjects, which results in a diminished response with standing. In parallel, there seems to be no marked alteration in vagal nor in /spl beta/-sympathetic activity in the H group.