Age-related changes in phase-space distribution of ABPM data in normotensive and hypertensive patients.

The data collected by ambulatory blood pressure monitoring have been studied in the phase-space of R-R interval and blood pressure and their individual distribution quantified by the slope of the regression line through 24-h values. This slope has been termed "ambulatory autonomic reciprocity index" and abbreviated as AARIs and AARId, the "s" and "d" indicating the relation with systolic and diastolic blood pressure respectively. Ambulatory monitoring was performed in 200 normotensive (NT: 135 females) and 200 untreated hypertensive patients (HT: 59 females).

The 24 h blood pressure-R-R interval relation in ambulatory monitoring.

The present study was aimed at investigating whether the blood pressure-R-R interval relation obtained by ABPM may give useful information about autonomic control in the 24 h period. To this purpose ABPM was performed in 60 healthy young subjects (30 females and 30 males, mean age 21.8+/-1.

A definition of internal constancy and homeostasis in the context of non-equilibrium thermodynamics.

The constancy of the internal environment, internal homeostasis, and its stability are necessary conditions for the survival of a biological system within its environment. These have never been clearly defined. For this purpose nonequilibrium thermodynamics is taken as a reference, and the essential principles of equilibrium, reversibility, stationary steady state and stability (Lyapounov, asymptotic, local and global), are briefly illustrated.

A thermodynamic model of the sympathetic and parasympathetic nervous systems.

In light of the nonequilibrium thermodynamics by I. Prigogine, the autonomic nervous system as a whole may be viewed as a dissipative structure progressively assembled in the course of evolution, plastically and rhythmically interfaced between forebrain, internal and external environments, to regulate energy, matter and information exchanges. In the present paper, this hypothesis is further pursued to verify whether the two main divisions of the autonomic nervous system, the sympathetic and parasympathetic systems, may support different types of exchange with the external environment.

Factors influencing acute ischaemia-induced renal hypertension in rats.

Objective: To verify if the acute hypertension that occurs after reversal of complete renal ischaemia is related to the duration of ischaemia, is different in one-kidney (1K) and two-kidney (2K) rats, and is prevented by angiotensin receptor blockade.

Methods: Four groups of Sprague-Dawley rats anaesthetized with pentobarbitone were studied before, during and after a reversible, complete renal ischaemia achieved by functional right nephrectomy.

Results: In 1K rats (group 1, n = 21), reopening of right renal hilum after functional right nephrectomy of 180, 60 and 30 min was followed by peak increases in systolic blood pressure of 76.