Time-frequency decomposition of HR and BP variability in reflex syncope

The autonomic control plays an essential role in the pathogenesis of reflex syncope. Still, the precise etiology of syncope is not completely understood and the clinical diagnosis of its origin remains rough and empirical. Head Up Tilt (HUT) test is used to reproduce symptoms. We have applied time frequency decomposition of HRV and BPV, which allows to evaluate the exact time evolution of the autonomic activity even during the transient stages of the HUT and syncope. We have observed, in typical vasovagal syncope, the sympathetic withdrawal, and the subsequent vagal surge. We have also been able to show that no vagal surge occurs at the instant of vasodepressor syncope. We have observed that the vagal activity is enhanced and the sympatho-vagal balance is lower in tilted position among subjects with positive HUT as compared to negative HUT.