[Autonomous nervous regulation of circulation during prolonged isolation studied with analysis of the cardiac rhythm...

Adjusting reactions of human body were evaluated using mathematical analysis of the cardiac rhythm. Variability of cardiac intervals was reduced in consequence of an elevation of sympathetic tone within the autonomous nervous system. Analyzed were diurnal arrays of cardiac intervals derived from Holter monitoring data. Pulse rate and standard deviation of the cardiac interval length were calculated for each of the 5-minute periods of recording. These data were used to calculate values of the parameters per an hour, 8 hours, and 24 hours. The analysis revealed that generally the body stress-reaction to prolonged isolation consists of increased strain of regulating systems in an effort to mobilize functional reserves. Depending on individual characteristics and functional reserves, the regulating systems become overstrained at some time-point and higher level regulators may be involved in adaptation. Criteria of overstrain include exaggerated pulse rate versus rising standard deviation. Combination of these shifts during morning and night hours should be qualified as least favorable. Test-subject 003, in whom regulation overstrain has been never observed in the experiment, was distinguished by the largest functional reserve.