RESUMEN
AIM: To compare autonomic nervous system activity estimated by power spectral analysis of heart rate variability in patients with vasovagal syncopes and healthy volunteers. MATERIAL AND METHODS: Seventeen health volunteers and 25 patients with vasovagal syncope were included in the study. In 16 cases faints were induced by head-up tilt table test (HTT), in 9 cases--by bicycle exercise test (BET). Power spectral analysis of heart rate variability in 5-th min ECG records was performed in supine and upright position while breath was fixed. RESULTS: In supine position the data of low frequency (LF) and high frequency (HF) of spectral power in both groups of patients were significantly higher than in volunteers. During upright the HF of spectral power significantly decreased in patients and volunteers. In upright position LF of spectral power significantly decreased in patients with syncope induced by HTT, did not change in patients with syncope induced by BET, but significantly increased in volunteers. CONCLUSION: Patients with vasovagal syncope had abnormal autonomic nervous system activity: a high level of parasympathetic influence in supine position and poor reaction of sympathetic nervous system during upright.