The objective of the work was to assess changes and the dynamics of changes on the parameters of heart rate variability (HRV) during and after a mental stress (MS) caused by an arithmetic test, to assess the suitability of the method of spectral analysis of HRV for evaluation of the response of the heart rate to mental stress in young subjects and assess possible differences between boys and girls. A total of 29 subjects were examined (14 girls, 15 boys) aged 19 - 21 years. The probands were examined by the Varia-Pulse TF3 system (Sima Media, Olomouc) in a sedentary position in the following sequence: recording of HRV at rest (T1), during mental stress (T2), immediately after mental stress (T3) and after a 5 - 10-minute interval following termination of mental stress (T4). Recording of the HRV at different time intervals took 5 minutes. To induce mental stress the adding test was used „PMT-psychomotor rate“ (Psycho-soft-system, P sychodiagnostika a.s., Bratislava) during which the probands were disturbed by a metronome. The evaluated parameters were: R-R interval, MSSD, total power, power VLF, LF, HF and VLF/HF ratio. The values were evaluated by the Wilcoxon and Mann-Whitney test. During mental stress (T2), as compared with the state at rest (T1) the R-R intervals were significantly reduced (p < 0.01), MSSD, power LF, HF declined significantly (p < 0.01), power VLF and ratio VLF/HF increased significantly (p < 0.01). During the 5 minutes following mental stress (T3), as compared with mental stress (T2), the R-R intervals were significantly prolonged (p < 0.01), MSSD, power LF, HF increased significantly (p < 0.01) and the power VLF and VLF/HF ratio declined (p < 0.01). During the 5 - 10-minute period after termination of mental stress the values of the investigated parameters did not differ from baseline values. The increment of the spectral value in the VLF area (power VLF) was during mental stress in girls significantly higher than in boys, similarly as the VLF/HF ratio (p < 0.02). Evaluation of HRV by spectral analysis using evaluation of spectral values in areas reflecting in particular the activity of the sympathetic nerve (VLF) and of the parasympathetic nerve (HF) revealed that it is a suitable method for assessment of the effect of mental stress on the regulation of the heart rate.

        Key words: young people, heart rate, spectral analysis, mental stress