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The 24 hour relation between R-R interval and diastolic blood pressure measured by ambulatory blood pressure monitoring.
No full textTHE 24 HOURS RELATION BETWEEN RR INTERVAL AND DIASTOLIC BLOOD PRESSURE CHANGES ±MEASURED BY AMBULATORY BLOOD PRESSURE MONITORING
G. Recordati, A. Zanchetti. Centro Fisiologia Clinica ed Ipertensione. Universita’ degli Studi ed Ospedare Maggiore. Milano. Italy
Background: The day and night circadian rhythm is accompanied by reciprocal changes in vagal and sympathetic dominance which may be quantified by measuring the R-R interval (R-R) and diastolic blood pressure (DBP) changes relation with ambulatory blood pressure monitoring (ABPM). Methods: ABPM was performed using Spacelabs monitors in 60 healthy young subjects (30 females and 30 males aged 21.8±1.0) with readings every 15 min (day) and 20 min (night). The collected variables were copied to a software program (Diadem. National Instruments) and R-R values obtained by dividing 60.000 by heart rate in beats/min. The following measurements were made: 1) night and day means ± SD: 2) night less day R-R (Δy, msec) and DBP (Δx. mmHg) differences and Δy/Δx ratios (ms/mmHg): 3) percent :Δy, Δx changes over day mean values and their ratio and 4) slope (b _24h) and r coefficient (r_24h) of the regression of R-R over DBP 24 hours values. Results: With respect to day. night was characterized by lengthenirg of R-R and lowering of DSP values in all subjects. The R-R and DBP day and night means ± SD. the night less day differences and the Δy/Δx ratios, both actual and percent. and the b_24h were different and characteristic for each subject. The r _24h reached statistical significance in all subjects Subjects were classified according to their proportionality ratios between R-R and DBP changes: two subjects had a Δy/Δx ratio below -5, 18 between -5 and -10, 28 between -10 and -20 and 12 above -20 ms/mmHg (range: -41.1 to -4.6. mean -14.6 ms/mmHg). The percent Δy/Δx ratio ranged from -32 to -0.5, mean -1.3 and the slope, b_24h, ranged from -14.28 to -3.14, mean -9.12 ms/mmHg. Conclusions: Results indicate that the ABPM may allow to quantify the individual's day—night autonomic reciprocity and that the subjects with steeper proportionality ratios have a higher 24h period vagal tone. This novel approach may thus be helpful to study the autonomic balance in several patients groups and the individual effects of different pharmacologjcal treatments
Age-related changes of phase-space distribution of ambulatory blood pressure monitoring data in normo- and hypertensive patients
No full textAGE-RELATED CHANGES OF PHASE-SPACE DIS TRIBUTION OF AMBULATORY BLOOD PRESSURE MONITORING (ABPM) DATA IN NORMO- ANDHYPERTENSIVE PATIENTS.
G. Recordati, G. Ponticelli, Medicina Cardiovascolare, Universita' degli Studi ed Ospedale Maggiore (Milano, Italy)
Objective: In addition to time domain, the ABPM data may be studied in the phase-space of R-R interval and blood pressurel.Methods: The individual phase-space distribution of data may be quantified by the negative slope of the regression line through 24 hour values of R-R interval over systolic (SBP) and diastolic blood pressures (DBP). Results: In 170 normotensive (N, SBP: 118.0 ± 8.0 24 mean ± sd, DBP: 72.7 ± 6.8 mmHg) and 181 untreated hypertensive subjects (H, SBP: 137.0 ± 8.0, DBP: 87.2 ± 6.8) the average slope of R-R interval over SBP was -5.7 ± 2.5 and -4.4 ± 2.4 ms*mmHg-1 respectively (p < 0.000). When distributed by decades of life the steepest slope occurred during the 20-29 decade (R-R/SBP, N: -7.7 ± 1.6; H: -6.3 ± 2.3) and the flattest in the 60-69 decade (R-R/SBP, N: -3.9 ± 2.0; H: -3.9 ± 1.4). The average slope was steeper from 20 to 59 years in normotensive than in hypertensive group and statistically significantly different at 40-49 (p<0.01) and 50-59 (p<0.05) years for R-R interval over both SBP and DBP. In the oldest subjects the regression slope was similar in both groups. The ambulatory arterial stiffness index (AASI) calculated on the same subjects from 20-29 to 60-69 decades increased linearly though similarly in both groups.Conclusions: When seen in the context of the "Autonomic space" by G.G. Berntson these data indicate that cardiovagal function is maximal at 20-29 years, declining thereafter and leveling off to the minimum of 60-69 decade. From 20 to 59 years of age the cardiovagal tone of hypertensive subjects seems to be constrained not only by an age effect but also by a sympathetic prevalence. References: 1) Recordati G. & Zanchetti A., Autonom. Neurosci: Basic & Clin.: 139, 68-77, 2008
The Visceral Nervous System: homeostasis and the dissipative structure.
No full textTHE VISCERAL NERVOUS SYSTEM (VNS): HOMEOSTASIS AND THE DISSIPATIVE STRUCTURE
Giorgio Recordati
Centro di Fisiologio Clinica e Ipertensione, University of Milano, Italy
Since the work of W. B. Cannon, the concept of reflex regulation of visceral function has usually been associated with that of negative feedback regulation for the purpose of Homeostasis. Homeostasis has been used to indicate either the constancy, inside a physiological range of the measured variable, and either the deterministic organization of function, necessary to survival, despite the threatening environmental stimuli. This term implies a mechanical, physical model of reference. Although the contradictory aspects of Cannon's Homeostasis and Emergency theories have been previously discussed (Recordati G., Arch. It. Biol. 122, 1984), this critique may be further pursued: 1) Of the two regulatory systems, endocrine and nervous system, we now know that the constancy of the fluid matrix is first of all guaranteed by the metabolism and the endocrine system. Examples are: the constancy of body temperature, glycemia, natremia and acid-base balance. 2) The concept of reflex regulation needs to be uncoupled from that of the feedback regulation and the linear causality, between stimulus and response, that it implies. Between the regulated variable and the stimulus on the sensory component, there is a multiplicity of interposed events which make the "circular causality" the most reasonable description of a biological causality (Yates F. E., In: Self-organizing systems, p. 347-350, Ed. F. E. Yates, Plenum, 1987). Some of the organizational principles which characterize the VNS's function and that distinguish it from the endocrine system and Homeostatic theory are: 1) The biological system is an open system which exchanges ENERGY, MATERIAL and INFORMATION with its environment. The nervous system in general and the VNS in particular is the apparatus which allows the biological system to be open to the environment: it is the interface between outside and inside environment. 2) This interface, which possesses a high degree of complexity in its internal organization, is characterized by plasticity and dynamicity of function, both at the peripheral and at the central level. Plasticity is maximal in embrionic and early life, but persists in adulthood (Black I. B. et al, Science 225, 1984). 3) The concept of the nervous center is now being substituted by that of the dynamic central regulation of function. 4) The VNS's development of internal functional organization is dependent on its relationships with the external and internal environments: the VNS keeps its internal organization as a function of the stimulus. The physical model which may be used to describe these organizational principles is that of the thermodynamics of non-equilibrium, i. e. the DISSIPATIVE STRUCTURE of I. Prigogine (Science 201, 1978). From this point of view, the function of both the sympathetic (SNS) and parasympathetic (PSNS) systems will be to use free energy to do work. If thermodynamic equilibrium is taken as reference, the SNS will then move the visceral system far away from equilibrium, and the PSNS towards it. While the SNS will be mainly related to the exchange of energy and increase gradients, the PSNS will be mainly related to the exchange of material and decrease gradients. The term information originates during phylogeny and may be described as the result of a relational constrain on the dynamic and unstable behavior of the system: the new structure exhibits a pattern which is stable with respect to the chance events of the previous level. Instability is thus a necessary condition for the appearance of information-dependent behaviors (Pattee H. H., In: Self-organizing systems, p. 325-338, Ed. F. E. Yates, Plenum, 1987). This hypothesis, which is a reproposal of the ergotropictrophotropic theory of W. R. Hess, allows to include both Homeostasis, as the description of a simplified system near equilibrium, and the Emergency theory, as the description of a complex system far away from equilibrium. It may also help to explain other hypothesis so far formulated and apparently contradictory, such as the "Pattern of response" of S. M. Hilton, and the "Dynamic specificity" of P. Langhorst. The mechanical model of the Homeostatic theory, does not allow, instead, this integrative approach. Despite their limits, teleology for Homeostasis and epistemological reductionism for the Dissipative Structure, it is suggested that, by the mean time, both theories might be complementary used to attempt a comprehensive view of the function of the VNS
The contribution of the giraffe to hemodynamic knowledge : a unified physical principle for the circulation
No full textHemodynamics stands on three main physical principles: the hydrostatic pressure, firstly described by Stevino, the viscous flow pressure, described by Poiseuille and the total hydraulic energy, or Bernoulli's equation. However, neither of these physical principles gives a comprehensive description of the single pressure measurement in the cardiovascular system. Hence, all these principles should be used together to fully describe the physical forces acting in the circulation of blood. Experiments that measured the hydrostatic pressure in the jugular vein of the giraffe have shown that a few guidelines need to be followed to measure it correctly. Following these guidelines, it can be seen that hydrostatic and viscous flow pressures are strictly related to one another, and that this relationship is described in mathematical terms. In addition, it has been shown that hydrostatic and viscous pressures should be included in Bernoulli's principle, to give the combined Bernoulli-Poiseuille equation. This unified principle is helpful not only to measure correctly the pressure with a catheter connected to a pressure transducer, but also to give to the pressure measured in a patient with the mercury manometer, a strong connection with the description of the pressure as a physical force acting inside the circulation. In addition it provides a comprehensive view of the cardiovascular system as a closed hydrodynamic system, in which the heart is a pump, that does not normally work to overcome the force of gravity. The question at this point is: are there any pathophysiological conditions in which the heart needs to be confronted with the sudden appearance of the force of gravity inside the cardiovascular system
Variazioni eta'-dipendenti in soggetti normo- ed ipertesi del monitoraggio ambulatoriale della pressione arteriosa nello spazio-di-fase autonomico : l'indice ambulatoriale di reciprocita' simpato-vagale
No full textThe visceral nervous system and its environments
Full text linkStarting from the observation of the relationships of the biological system with its environments and of the genetically determined neuronal properties of plasticity and rhythmicity, it is possible to propose a new hypothesis about the functional role and organization of the visceral nervous system based on the physical model of the Dissipative Structure by I. Prigogine. The similarily between the visceral nervous system function and this model is supported by the following observations: (1) The visceral nervous system is a complex system, composed of many interacting units, which works away from thermodynamic equilibrium; (2) the functional organization of the nervous system is strongly dependent on internal and external environmental stimuli; (3) it is characterized by the presence of rhythms and periodic behaviors and (4) the internal order of the system is maintained in the continuous interplay between function, structure and fluctuations. On the basis of the present hypothesis, a few general principles can be formulated: (1) the higher brain centers, the fluid matrix and the external world, are the visceral nervous system natural environments; (2) with which it is plastically interfaced as a thermodynamic dissipative structure; (3) its main functional role is to regulate, distribute and maintain ordered exchanges of matter, energy and information between these environments. The present is a general interpretation of the operations of the visceral nervous system as a whole. In the frame of this interpretation the hypotheses so far formulated, including the homeostatic theory, can be viewed as the description of discrete and complementary aspects of the visceral nervous system functions
The functional role of the visceral nervous system. A critical evaluation of Cannon's homeostatic and emergency theories
No full textDeterminismo, indeterminismo, omeostasi ed organizzazione funzionale del sistema nervoso viscerale
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Type A atrial receptors in the cat : effects of changes in atrial volume and contractility
No full textAction potentials were recorded from filaments of the right cervical vagus in anaesthetized, paralysed cats. Right atrial receptors with type A (twelve units) and Intermediate type (two units) patterns of spontaneous discharge were selected and their responses to changes in atrial volume were analysed. Changes in atrial volume of similar magnitude were produced under four different conditions: a, innervated hearts; b, denervated hearts; c, depression of atrial muscle contractility induced after cardiac denervation and d, non-beating hearts. In innervated hearts the systolic discharge of each receptor showed a characteristic response to changes in atrial volume. Cardiac denervation and depression of atrial contractility markedly altered this response in terms of frequency of discharge, threshold and 'sensitivity'. During increments in atrial volume all the receptors but one assumed an Intermediate pattern of discharge. The diastolic firing rate was, however, higher for any given atrial pressure, in innervated hearts than under conditions b, c and d. In innervated hearts the response of the receptors to atrial systole was characterized by a higher frequency of discharge and a lower threshold with respect to the responses of the same receptors to atrial filling. These differences were minimized at high atrial volumes and during depression of atrial contractility. The results indicate that the responses of the receptors to atrial systole are mainly dependent upon the state of contraction of atrial muscle and that the differences between systolic and diastolic discharge are mainly due to the high dynamic component of the stretch during atrial contraction
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