Experimental and clinical physiology and biochemistry, ECPB 2019, 2(86): 11-23. https://doi.org/ hand, and HRV and EEG, on the other hand, as well as between changes in the immune and neural parameters caused by balneotherapy [15,16,17,18,19,20]. Hence, a hypothesis that, for the same states of the autonomic nervous system, the differences in immune responses to chronic stress were due to the features of the EEG. The verification of this hypothesis was the goal of this study. Material and methods. The object of observation were 32 men (aged 24-70 years old) and 8 women (39-71 years old) with chronic pyelonephritis in remission. The criterion for inclusion was the magnitude of the sympatho-vagal balance index LF/HF which exceeded the age norm by 0,5 σ.We recorded the electrocardiogram for 7 min in II group to assess the parameters of HRV [21,22] (software and hardware complex "CardioLab+HRV" produced by "KhAI-MEDICA", Kharkiv, Ukraine). For the further analysis the following parameters of heart rate variability (HRV) were selected. Temporal parameters (Time Domain Methods): the standard deviation of all NN intervals (SDNN), the square root of the mean of the sum of the squares of differences between adjacent NN intervals (RMSSD), the percent of interval differences of successive NN intervals greater than 50 ms (pNN 50 ). Spectral parameters (Frequency Domain Methods): spectral power density (SPD) bands of HRV: high-frequency (HF, range 0,4÷0,15 Hz), low-frequency (LF, range 0,15÷0,04 Hz), very low-frequency (VLF, range 0,04÷0,015 Hz) and ultra low-frequency (ULF, range 0,015÷0,003 Hz). Classical indexes were calculated: LF/HF, LFnu =100 %•LF/(LF+HF) and Baevskiy's Activity Regulatory Systems Index (BARSI) as well as the Entropy (h) of normalized SPD using CE Shannon's formula: hHRV = -[SPD HF•log 2 SPD HF + SPD LF•log 2 SPD LF + + SPD VLF•log 2 SPD VLF + SPD ULF•log 2 SPD ULF]/log 2 4. Experimental and clinical physiology and biochemistry, ECPB 2019, 2(86): 11-23. https://doi.org/