The autonomic control in vasovagal syncope investigated by spectral and time-dependent analysis of heart rate fluctuations

Spectral analysis of heart rate fluctuations was used to investigate the role of the autonomic nervous system in the pathogenesis of vasovagal syncope. Patients with recurrent episodes of unexplained syncope and normal controls were studied in supine and in 60° head-up tilt position applied as a test of the propensity to reflex neurocardiogenic syncope. Heart rate variability was analyzed in the context of physiological changes in mean heart rate, systolic and diastolic blood pressure and pulse pressure. In order to study nonstationary periods during the experiment a time dependent analysis was developed and applied in some cases. The results are consistent with a lower sympathetic reserve in patients. The authors concluded also that prolonged orthostatic stress may induce reflex fainting in normal young subjects