The effect of a 2-week tail suspension on mean arterial pressure (MAP) and pulse interval (PI) was studied in conscious chronically instrumented intact and sympathectomized rats. Sympathectomy was induced by 6-hydroxydopamine (100 mg x kg(-1), i.v.), injected 1 day before, and on days 5 and 10 of suspension. During suspension the intact rats had the same levels of MAP and PI as the intact controls. After release from suspension their MAP did not change: PI decreased (by 9%), but only for 1 h. Sympathectomy augmented the haemodynamic changes after release from suspension: tachycardia (10%) and hypotension (19%) were observed during the entire recording period (2 h). Therefore, in rats, post-suspension hypotension becomes apparent only after elimination of sympathetic influences. In spite of unaltered systemic parameters, intact post-suspension rats showed diminished responses to intravenous administration of tyramine (100 microg x kg(-1)) and phenylephrine (1-2 microg x kg(-1)). In addition, they showed augmented haemodynamic changes associated with natural behaviour. The increase of MAP and the decrease of PI on transition from rest to movement were more pronounced in the intact post-suspension rats than in the control rats (MAP 8.3% vs 4.5%, PI 15% vs 9%). In control rats the spectrum power density of low-frequency (0.0195-0.25 Hz) MAP fluctuations depended only weakly on behavioural activity, whereas in post-suspension intact rats it was profoundly augmented during movements (by 170%). Since the rapid adjustment of haemodynamics to behavioural activity is controlled by the sympathetic nervous system, the unbalanced condition of the cardiovascular system after suspension may reflect an altered sympathetic nerve control of the circulation.
The study analyzed changes in parameters of the central and intracardiac hemodynamics during the development of experimental arterial hypertension, which were assessed as the adaptive in nature. The development of hypertension demonstrated staging of the adaptive processes. The development of the adaptive responses was characterized by changes in the magnitude and probabilistic distribution of the hemodynamic parameters.
Trivariate correlation analysis of hemodynamic indices of the cardiovascular system in rabbits with diphtheria showed that adaptation of this system to direct action of diphtherin can be visualized by analysis of trivariate correlation tightness for indices of intraventricular pressure in the left and right ventricles and indices of systemic blood pressure. Using empirical production functions for systemic blood pressure indices we found that the contribution of intraventricular pressure in the left and right ventricles on blood pressure values is changed in diphtheria compared to the control. Basing on entropy analysis we established that the regimen of control over values of working intraventricular pressure in both left and right ventricles in diphtheria is changed from quasidetermined to stochastic.
Analysis of the effects of seasonal changes in the myocardium on variability of arterial and intraventricular pressure in both ventricles showed that the objects of homeostatic regulation were the values of these parameters and their probability distribution. The adaptation mechanisms are mainly visualized by the analysis of the characteristics of probability distribution of the parameters (asymmetry and excess coefficients).
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