Changes of the autonomous nervous tonus are considered the most important factor in the pathogenesis of vasovagal syncope. In order to investigate changes of the autonomous tonus the authors examined in patients with vasovagal syncope the variability during the head-up tilt test (HUT). In 35 patients with assumed vasovagal syncope the authors used a passive HUT (45 mins., 60 degrees) and subsequently nitroglycerintimulated HUT (0.4 mg s.l,15 mins.). The heart rate variability was evaluated before the onset of the test in a horizontal position, immediately after tilting the patient (0 min.), during the 5th, 10th, 15th minute of the passive test, during the 5th minute of the nitroglycerin test, during the appearance of symptoms and after termination of the test in a horizontal position. They compared the results between a group of 20 patients with positive HUT (13 men, 36 years) and in 15 patients with a negative HUT (7 men, 32 years). The parameters of heart rate variability were during the development of the syncope (mean 6.4 mins. after administration of NTG) as compared with corresponding values in patients with negative HUT (during the 5th minute after administration of NTG) as follows: RR interval 759.6 ± 248.1 ms vs. 552.1 ± 88.7 ms (p = 0.01), SDNN 44.8 ± 49.6 vs. 29.9 ± 18.3 (p = 0.001), RMSSD 31.8 ± 34.9 vs. 15.2 ± 10.2 (p = 0.03), LF 4.44 ± 0.66 lnms 2 vs.4.38 ± 0.53 lnms 2 (p = 0.82), HF 4.44 ± 0.57 lnms 2 vs. 4.39 ± 0.45 lnms 2 (p = 0.82), LF/HF 0.99 ± 0.03 vs. 0.99 ± 0.02 (p = 0.90). On development of the first presyncopal manifestations the statistical parameters of heart rate variability in patients with positive HUT were significantly higher as compared with patients with negative HUT, which suggests an increase of the parasympathetic autonomous tonus during the development of the vasovagal syncope.

        Key words: Vasovagal syncope - Autonomous nervous system - Variability of pulse rate - Head-up tilt test