Normalized entropy applied to the analysis of interindividual and gender-related differences in the cardiovascular effects of stress

Abstract

Nonlinear dynamic methods are considered to be a potential tool for studying the complex behavior of the cardiovascular system. In the present study, interindividual and gender-related differences in cardiovascular (CV) responses to various stress stimuli were studied using conventional CV variables such as heart rate (HR) and blood pressure (BP), as well as a recently introduced criterion of system complexity, normalized entropy (E/H, where E is entropy and H is system energy). A group of healthy students (n = 270) of both genders (17-20 years of age) were subjected to noise exposure, mental arithmetic, arithmetic against noise and examination stress. Results showed that CV reactivity depended upon the kind of stress imposed and the gender of the subject. HR and BP stress-induced responses did not differ between men and women. However, men had higher absolute BP levels at baseline and during exposure to stressors. Stress-induced pressor responses lasted longer in men than in women. Changes in the complexity degree of CV signals, as assessed by E/H, were more pronounced and prolonged than those of HR and BP. Unlike the latter, E/H changed significantly in all stress situations for each subject tested and could be divided into two types of stress-induced response. These results allow one to conclude that E/H can better quantitate individual differences in CV stress reactivity in comparison with HR and BP. These findings suggest that stress-induced changes in CV functioning are more varied than can be revealed by applying conventional CV measures.

Sex-related differences in cardiovascular stress reactivity in healthy and hypertensive rats

“…In humans, the cardiovascular stress response is also characterized by more pronounced chronotropic effects in women and more potent HT reaction in men [4,6,13]. HR and MBP in stressed females returned to normal more rapidly than in males, which is consistent with published data on animals [15] and humans [4,6,13].…”

Vascular and Cardiac Effects of Stress in Albino Rats of Different Sex and Age Groups

“…Therefore, the cardiovascular stress-reactivity in adult rats is characterized by the predominance of the cardiac component over the vascular component, particularly in females. These data are consistent with the results of observations on humans [2,5]. The reduced vascular reactivity in females during RS (as compared to that in males) can be related to a higher concentration of NO and is associated with high resistance to renal hypertension [1].…”

Valsalva ratio: a measure of stress in first year medical students

“…4,5,6 Only a few studies have investigated the impact of acute stressor on various HR complexity measures in healthy individuals. 7,8 It was shown in healthy young subjects that short term psychological stress was associated with both decrease and increase in heart rate complexity (that is normalized entropy) regardless of type of stressors such as Noise exposure, exam stress etc., 8 Under normal condition the Heart rate generating system fluctuates between a set of metastable states or attraction ready to adapt to internal or external challenges of an ever changing environment. 8,9 Thus reduction in Heart rate complexity during stressful condition may represent a lower adaptability and fitness of the cardiac parameters and a functional restriction of the participating cardiovascular elements.…”