Physiological methods and methods of nonlinear dynamics
in evaluation of cardiovascular effects of stress in humans
T.G. Anishchenko 
, N.B. Igosheva , P.I. Saparin 
Department of Biology, Saratov State University, Russia;
Laboratory of Nonlinear Dynamics, Department of Physics,
Saratov State University, Russia
The purpose of this study was to investigate the individual and sex particularities in human cardiovascular responses to different stress stimuli, using the traditional physioigycal approach and the methods of dynamical systems theory. Measurements were taken in 85 healthy men and 115 women exposed to noise stress, double mental arithmetic stress and arithmetic against noise. Results showed that, firstly, cardiovascular reactivity in men and women was determined by the type of stress. Thus, in a majority of humans heart rate did not change during noise but increased during mental and mental associated with noise. Blood pressure decreased during noise but increased during mental and mental combined with noise. Secondly, results demonstrated the significant sex differences in the basal and stress cardiovascular activity. The women showing the greater basal and stress heart rate displayed the hypotensive responses to noise more often and hypertensive responses to mental less often then men. During noise and mental against noise the basal and stress levels of blood pressure were less in women than in men. Thirdly, the changes in normalized entropy, which is Shannon entropy related to the system enerdy (Yu.L. Klimontovich, 1989, V.S. Anishchenko, P.I. Saparin, T.G. Anishchenko, N.B. Igosheva, 1993) also depend on the sex of the subjects and the nature of the stress. During noise normalized entropy increased in majority of women but decreased in a majority of men. Mental stress and mental against the noise caused both decreases and increases in normalized entropy in men and women. But the increases in normalized entropy dyring these types of stress and especially during recovery were greater in women than in men. Normalized entropy was demonstrated to be more sensitive marker of sex and individual differences in cardiovascular responses to external influences than heart rate and blood pressure. Results suggest that the lower blood pressure reactions and the greater increases in the normalized entropy, i.e. in physiological heart variability may result in higher cardiovascular stress resistance in women relative to men.