OBJECTIVE: The objective of the submitted work was to assess by the method of spectral analysis of the heart rate how the use of bisoprolol will affect the autonomous modulation of the heart rate in hyperthyroid patients and what are the time relations of this effect.

MATERIAL AND METHODS: In the investigation 10 female patients with thyreotoxicosis caused by Graves-Basedow's disease were included. Their average age was 38 years and along with a thyrostatic drug bisoprolol was administered. Spectral analysis of the heart rate was made before the onset of treatment, after a week and after six weeks with the patients in an upright and recumbent position. The activity of the sympathicus was evaluated from the ratio of low and high frequencies.

RESULTS: Already during the first week a significant decline of the heart rate was observed. During the first week of treatment a decline of the activity of the sympathicus in a recumbent position occurred associated with milder palpitations or their complete disappearance. The decline in an upright position occurred after the first week of treatment. From the trend of other parameters of cardiac variability, the differences of some reached statistical significance, it may be concluded that the activity of the parasympathicus, formerly inhibited, was restored.

CONCLUSION: Based on the results it may be stated that bisoprolol is a suitable supplementary drug in the early treatment of thyrotoxicosis because by reducing the hyperadrenergic state it improves the quality of life of these patients.

Keywords: Adolescent; Adrenergic beta-Antagonists /therapeutic use/; Adult; Bisoprolol /therapeutic use/; Electrocardiography; Female; Graves Disease /complications/; Heart Rate /drug effects/; Humans; Middle Aged; Signal Processing, Computer-Assisted; Thyrotoxicosis /physiopathology/