[Heart rhythm indices during human solving of arithmetic tasks].

Heart rate and respiration were recorded in a group of 90 subjects (25 males and 65 females) aged 17-19 during rest and under informational load (arithmetical tasks) lasting 3 min each. Off-line spectral analysis was performed for all the subjects. Anxiety according to Spilberger and strength of excitation-inhibition according to Strelau were also tested. It was shown that heart rate increased significantly in the group as a whole, however, variability of RR-intervals remained unchanged. Then two subgroups of subjects who responded to information load by a decrease and increase of RR-interval variability were distinguished. These subgroups were characterized respectively by the high and low levels of personal anxiety. The decrease of RR-interval variability in the high-anxiety subgroup was associated with a decrease of power in all frequency bands of the rate spectrum. The increase of RR-interval variability in the low-anxiety subground was due to an increase of heart rate modulation in a low-frequency band of the heart rate spectrum. Fatigue is regarded as a cause of such heart rate modulation.