Effect of chronic denervation on blood flow and ultrastructural and functional status of the tubule system of the solitary kidney

The sodium kidney treatment, local blood flow in the cortex and medulla as well as ultrametric parameters of mitochondria of different regions of the rat kidney duct system were studied under compensatory hypertrophy of kidneys (CHK) and against a background of aftereffects of single kidney decentralization (SKD). In all 120 experiments have been conducted. In the course of the first two weeks of the experiment the local blood flows in the cortex of SKD increased by 30% as compared to those under CHK and natriuresis+ was thrice as high (due to a decrease in proximal reabsorption). In this case coefficients of structural organization Km and of energy efficiency (Ke) of mitochondria lowered in cells of proximal ducts. Later on the intensity of local blood flows in the cortex of SKC was not only lower progressively than that under CHK but also of the control, simultaneously local blood flows in medulla being increased. The complete equalization of the sodium transport parameters of SKD up to their values under CHK did not occur. The rise of ultrametric parameters of the medullary ducts of SKD segments is associated with the intensification of their hemoperfusion.     

Control of coronary blood flow during exercise

Under normal physiological conditions, coronary blood flow is closely matched with the rate of myocardial oxygen consumption. This matching of flow and metabolism is physiologically important due to the limited oxygen extraction reserve of the heart. Thus, when myocardial oxygen consumption is increased, as during exercise, coronary vasodilation and increased oxygen delivery are critical to preventing myocardial underperfusion and ischemia. Exercise coronary vasodilation is thought to be mediated primarily by the production of local metabolic vasodilators released from cardiomyocytes secondary to an increase in myocardial oxygen consumption. However, despite various investigations into this mechanism, the mediator(s) of metabolic coronary vasodilation remain unknown. As will be seen in this review, the adenosine, K(+)(ATP) channel and nitric oxide hypotheses have been found to be inadequate, either alone or in combination as multiple redundant compensatory mechanisms. Prostaglandins and potassium are also not important in steady-state coronary flow regulation. Other factors such as ATP and endothelium-derived hyperpolarizing factors have been proposed as potential local metabolic factors, but have not been examined during exercise coronary vasodilation. In contrast, norepinephrine released from sympathetic nerve endings mediates a feed-forward betaadrenoceptor coronary vasodilation that accounts for approximately 25% of coronary vasodilation observed during exercise. There is also a feed-forward alpha-adrenoceptor-mediated vasoconstriction that helps maintain blood flow to the vulnerable subendocardium when heart rate, myocardial contractility, and oxygen consumption are elevated during exercise. Control of coronary blood flow during pathophysiological conditions such as hypertension, diabetes mellitus, and heart failure is also addressed.     

On the solution of the non-linear bio-heat equation

With reference to microwave localized hyperthermia, a non-linear model of the thermal behavior of living tissues, where local thermoregulating convective and conducting effects due to blood flow are taken into account, has been assumed. The non-linear operator equation for the space and time temperature distribution, which describes local energy balance (bio-heat equation), has been linearized and solved by using a variant of the Newton iterative method. Numerical calculations for plane stratified structures simulating living bodies, irradiated by plane electromagnetic waves, have been carried out.     

Hydromagnetic Flow and Heat Transfer over a Porous Oscillating Stretching Surface in a Viscoelastic Fluid with Porous Medium

An analysis is carried out to study the heat transfer in unsteady two-dimensional boundary layer flow of a magnetohydrodynamics (MHD) second grade fluid over a porous oscillating stretching surface embedded in porous medium. The flow is induced due to infinite elastic sheet which is stretched periodically. With the help of dimensionless variables, the governing flow equations are reduced to a system of non-linear partial differential equations. This system has been solved numerically using the finite difference scheme, in which a coordinate transformation is used to transform the semi-infinite physical space to a bounded computational domain. The influence of the involved parameters on the flow, the temperature distribution, the skin-friction coefficient and the local Nusselt number is shown and discussed in detail. The study reveals that an oscillatory sheet embedded in a fluid-saturated porous medium generates oscillatory motion in the fluid. The amplitude and phase of oscillations depends on the rheology of the fluid as well as on the other parameters coming through imposed boundary conditions, inclusion of body force term and permeability of the porous medium. It is found that amplitude of flow velocity increases with increasing viscoelastic and mass suction/injection parameters. However, it decreases with increasing the strength of the applied magnetic field. Moreover, the temperature of fluid is a decreasing function of viscoelastic parameter, mass suction/injection parameter and Prandtl number.     

Computational model of the fluid dynamics of a cannula inserted in a vessel: incidence of the presence of side holes in blood flow

Vascular access methods, performed by the insertion of cannulae into vessels, may disturb the physiological flow of blood, giving rise to non-physiological pressure variations and shear stresses. To date, the hydrodynamic behaviour of the cannulae has been evaluated comparing their pressure loss–flow rate relationships, as obtained from in vitro experiments using a monodimensional approach; this methodology neither furnish information about the local fluid dynamics nor the established flow field in specific clinical work conditions. Since the shear stress is a critical factor in the design of artificial circulatory devices, more knowledge should be necessary about the local values assumed by the haemodynamic parameters during cannulation. An alternative way to investigate the fluid dynamic as accurately as possible is given by numeric studies. A 3D model of cannula concentrically placed in a rigid wall vessel is presented, with the finite element methodology used to numerically simulate the steady-state flow field in two different venous cannulation case studies, with two cannulae having a central hole and two or four side holes, respectively, with the same boundary conditions. Lower velocity and shear stress peak values have been computed for the model with four side holes upstream of the central hole, in the region of the cannula where the inlet flows meet and towards cannula's outlet, due to the increased flow symmetry and inlet area with respect to the model with two side holes. Starting from the investigation of different cannula designs, numerically assessing the local fluid dynamics, indications can be drawn to support both the design phase and the device optimal clinical use, in order to limit risks of biomechanical origin. Thus the presence of four side holes implied, as a consequence of the greater inlet area and of the increased symmetry, a less disturbed blood flow, together with reduced shear stress values. Furthermore, results show that the numerical simulations furnished useful informations on the interaction between vessel and cannula, e.g. on the fluid dynamics establishing in the free luminal space left, in the vessel, by the inserted cannula.     

A Computational Model of the Fetal Circulation to Quantify Blood Redistribution in Intrauterine Growth Restriction

Intrauterine growth restriction (IUGR) due to placental insufficiency is associated with blood flow redistribution in order to maintain delivery of oxygenated blood to the brain. Given that, in the fetus the aortic isthmus (AoI) is a key arterial connection between the cerebral and placental circulations, quantifying AoI blood flow has been proposed to assess this brain sparing effect in clinical practice. While numerous clinical studies have studied this parameter, fundamental understanding of its determinant factors and its quantitative relation with other aspects of haemodynamic remodeling has been limited. Computational models of the cardiovascular circulation have been proposed for exactly this purpose since they allow both for studying the contributions from isolated parameters as well as estimating properties that cannot be directly assessed from clinical measurements. Therefore, a computational model of the fetal circulation was developed, including the key elements related to fetal blood redistribution and using measured cardiac outflow profiles to allow personalization. The model was first calibrated using patient-specific Doppler data from a healthy fetus. Next, in order to understand the contributions of the main parameters determining blood redistribution, AoI and middle cerebral artery (MCA) flow changes were studied by variation of cerebral and peripheral-placental resistances. Finally, to study how this affects an individual fetus, the model was fitted to three IUGR cases with different degrees of severity. In conclusion, the proposed computational model provides a good approximation to assess blood flow changes in the fetal circulation. The results support that while MCA flow is mainly determined by a fall in brain resistance, the AoI is influenced by a balance between increased peripheral-placental and decreased cerebral resistances. Personalizing the model allows for quantifying the balance between cerebral and peripheral-placental remodeling, thus providing potentially novel information to aid clinical follow up.     

Human males and females body thermoregulation: Perfusion effect analysis

Skin temperature is a common physiological parameter that reflects thermal responses. Blood perfusion is an important part of the physiological processes that the human body undergoes in order to maintain homeostasis. This study focuses on the effect of perfusion on the temperature distribution in human males and females body in different thermal environment. The study has been carried out for one dimensional steady cases using finite element method. The input parameter of the model is the blood perfusion or volumetric flow rate within the tissue. The appropriate physical and physiological parameters together with suitable boundary conditions that affect the heat regulations have been incorporated in the model. The study is to have a better understanding that how does thermoregulation change in human males and females skin layered due to perfusion.     

What measurements are necessary for a comprehensive evaluation of the peripheral arterial circulation?

Several methods are available to detect atherosclerotic lesions with a severe degree of stenosis (>70%), but the diagnosis of atherosclerotic lesions with no stenosis or with a minor degree of stenosis (<20%), is problematic. Hemodynamics associated with stenotic lesions are well described by the relationship of blood pressure and blood flow velocity, both as a function of time and localization (along the length and cross-section of the vessel). The use of this relationship in the clinic is difficult because no precise information is available about the geometry and branching of arteries, blood viscosity, and the velocity distribution over the cross-sectional area of the blood vessel. Besides, the invasiveness of the technique to measure arterial pressure as a function of time and localization does not allow routine application in patients. Because of these limitations, alternative methods have been developed. The degree and extensiveness of atherosclerotic disease can, for instance, be estimated from the changes in maximum blood flow velocity and in velocity profile, i.e., velocity distribution along the cross-section of the vessel. Moreover, the delay between simultaneously recorded arterial blood flow velocity tracings (pulse-wave velocity determination) is used to assess the elastic properties of the vessel. Changes in velocity profile occur at relatively slight degrees of arterial stenosis (around 20%), so that determination of these profiles along diseased arteries may contribute to the early diagnosis of atherosclerotic lesions. In man, transcutaneous information about the maximum and mean blood flow velocities over the cross-sectional area of the artery as an instantaneous function of time as well as the flow pattern can be obtained online with continuous wave Doppler flowmeters, at least when audio spectrum analysis is used as a processing technique. Velocity profiles can be determined with multichannel pulsed Doppler systems if the resolution of the system is adequate and a sufficient number of sample volumes can be obtained, limiting the interpolation between these samples. The on-line recording of velocity profiles can be facilitated by combining the pulsed Doppler device with either a velocity imaging system or a B-mode scan. In systems with a high resolution (sample distance 0.5 mm), one should be able to detect local disturbances in the velocity profile at the site of the lesion (due to local increases in shear stress) and proximal to the lesion (due to reflections), so that lesions with a minor degree of stenosis can be detected. In resistive systems (e.g., internal carotid arteries) in which the relationship between pressure and velocity changes during the cardiac cycle is relatively simple, the elasticity of the arterial wall can be determined by relating the relative diameter changes of the vessel, determined on-line with multichannel pulsed Doppler systems, to the instantaneous velocity pulse. Although the detection of atherosclerotic lesions at an early stage of the disease with sophisticated Doppler devices looks promising, further clinical evaluation is required.     

Temperature profiles with respect to inhomogeneity and geometry of the human body

Temperature profiles within the human body are highly dependent on the geometry and inhomogeneity of the body. Physical parameters such as density and heat conductivity of the various tissues and variables such as blood flow and metabolic heat production of different organs are spatially distributed and thereby influence the temperature profiles within the human body. Actual physiological knowledge allows one to take into account up to 54 different spatially distributed values for each parameter. An adequate representation of the anatomy of the body requires a spatial three-dimensional grid of at least 0.5-1.0 cm. This is achieved by photogrammetric treatment of three-dimensional anatomic models of the human body. As a first essential result, the simulation system has produced a realistic picture of the topography of temperatures under neutral conditions. Compatibility of reality and simulation was achieved solely on the basis of physical considerations and physiological data base. Therefore the simulation is suited to the extrapolation of temperature profiles that cannot be obtained experimentally.     

Simultaneous measurements of local tissue temperature and blood perfusion rate in the canine prostate during radio frequency thermal therapy

Local tissue temperature and blood perfusion rate were measured simultaneously to study thermoregulation in the canine prostate during transurethral radio-frequency (RF) thermal therapy. Thermistor bead microprobes measured interstitial temperatures and a thermal clearance method measured the prostatic blood perfusion rate under both normal and hyperthermic conditions. Increase in local tissue temperature induced by the RF heating increased blood perfusion throughout the entirety of most prostates. The onset of the initial increase in blood perfusion was sometimes triggered by a temporal temperature gradient at low tissue temperatures. When tissue temperature was higher than 41°C, however, the magnitude and the spatial gradient of temperature may play significant roles. It was found that the temperature elevation in response to the RF heating was closely coupled with local blood flow. The resulting decrease in or stabilization of tissue temperature suggested that blood flow might act as a negative feedback of tissue temperature in a closed control system. Results from this experiment provide insights into the regulation of local perfusion under hyperthermia. The information is important for accurate predictions of temperature during transurethral RF thermal therapy.     

Nervous control of the cerebrovascular system: doubts and facts.

Increased function of the central neurons results in increased neuronal metabolism and, as a consequence, increased concentration of metabolic end-products (H+, K+, adenosin) results in an increased cerebral blood flow (CBF). There is a general agreement among investigators that products of cerebral tissue metabolism as well as chemical stimuli are key factors that determine the rate of blood flow in the brain. CBF, however, may increase out of proportion to metabolic demands, may increase without significant change in local metabolism, and may increase much faster than the accumulation of the metabolic end-products. Therefore, the 100-year-old metabolic hypothesis of Roy and Sherrington, cannot fully explain the increases of CBF during increased functional activity of the central neurons. The tight coupling of neuronal activity and blood flow in the brain is demonstrated by a large amount of data. Therefore, the likelihood exists that neurogenic stimuli via perivascular nerve endings may act as rapid initiators, to induce a moment-to-moment dynamic adjustment of CBF to the metabolic demands, and further maintenance of these adjusted parameters is ensured by the metabolic and chemical factors. Perivascular nerve endings were identified in the outer smooth muscle layer of the cerebral arteries, arterioles and veins. Their axonterminals contain a large variety of neurotransmitters, often co-localised in synaptic vesicles. Stimulation of the nerves results in a release of transmitters into the narrow neuromuscular synaptic clefts in the cerebrovascular smooth muscle, close to specific receptor sites in the vessel wall. In spite of these facts, however, and in spite of the large number of new experimental evidences, the role of the nervous control of the cerebrovascular system is underestimated both in medical textbooks and in the common medical knowledge since decades. In the last 20 years major advances have been made that make it necessary to revise this false view. The purpose of this review is to facilitate this process at the end of this century, when the importance of the nervous control of the cerebral circulation has been fully appreciated among investigators.     

Steady state temperature distribution in dermal regions of an irregular tapered shaped human limb with variable eccentricity

The investigators in the past have developed some models of temperature distribution in the human limb assuming it as a regular circular or elliptical tapered cylinder. But in reality the limb is not of regular tapered cylindrical shape. The radius and eccentricity are not same throughout the limb. In view of above a model of temperature distribution in the irregular tapered elliptical shaped human limb is proposed for a three dimensional steady state case in this paper. The limb is assumed to be composed of multiple cylindrical substructures with variable radius and eccentricity. The mathematical model incorporates the effect of blood mass flow rate, metabolic activity and thermal conductivity. The outer surface is exposed to the environment and appropriate boundary conditions have been framed. The finite element method has been employed to obtain the solution. The temperature profiles have been computed in the dermal layers of a human limb and used to study the effect of shape, microstructure and biophysical parameters on temperature distribution in human limbs. The proposed model is one of the most realistic model as compared to conventional models as this can be effectively employed to every regular and nonregular structures of the body with variable radius and eccentricity to study the thermal behaviour.     

Effects of blood flow,curved boundary and environmental conditions on temperature distribution in a two dimensional model of human skin and subcutaneous tissues

A mathematical model for the study of the effects of blood flow, metabolic heat production, various environmental conditions and the presence of a curved boundary on the temperature distribution (TD) in a two dimensional model of human skin and subcutaneous tissues (SST) is presented. Based on physiological properties, the interfaces between epidermis-dermis (IED) and dermis-subcutaneous tissues (IDS) have been considered to be irregular and the regions of these layers have been divided into 109 triangular elements of various sizes which are connected with each other by 70 nodes. The results computed from this thermobiological mathematical model, using Galerkin's finite element technique, have been exhibited graphically. The effects of various environmental conditions, blood flow and metabolic heat production are found to be nonuniform on TD at the nodes situated at the same depth in SST. This nonuniformity in TD almost disappears at the nodes situated in dermis nearest to IDS except for the two of the six combinations, considered in the present study, in which highest values of blood flow and metabolic heat production have been considered. The rate of fall of temperature with respect to thickness (towards the skin surface) is higher at the straight boundary (SB) than at the curved boundary (CB). The temperature increases with respect to width (from SB to CB) in epidermis and dermis but decreases in subcutaneous tissues. This increase or decrease of temperature is more pronounced at the nodes situated near to, or at CB. The trend of these temperature profiles in SST reflects the dependence of TD not only on the environmental conditions and biophysical variables but also on the geometry of SST.     

Design of a side-view particle imaging velocimetry flow system for cell-substrate adhesion studies

Experimental models that mimic the flow conditions in microcapillaries have suggested that the local shear stresses and shear rates can mediate tumor cell and leukocyte arrest on the endothelium and subsequent sustained adhesion. However, further investigation has been limited by the lack of experimental models that allow quantitative measurement of the hydrodynamic environment over adherent cells. The purpose of this study was to develop a system capable of acquiring quantitative flow profiles over adherent cells. By combining the techniques of side-view imaging and particle image velocimetry (PIV), an in vitro model was constructed that is capable of obtaining quantitative flow data over cells adhering to the endothelium. The velocity over an adherent leukocyte was measured and the shear rate was calculated under low and high upstream wall shear. The microcapillary channel was modeled using computational fluid dynamics (CFD) and the calculated velocity profiles over cells under the low and high shear rates were compared to experimental results. The drag force applied to each cell by the fluid was then computed. This system provides a means for future study of the forces underlying adhesion by permitting characterization of the local hydrodynamic conditions over adherent cells.     

Investigation of the effect of exposure to non cytotoxic amounts of microcystins

This paper describes a metabolomic approach for investigation of the potential effect of exposure of humans to low amounts of microcystins using HepG2 cell line. Microcystins are hepatotoxins produced by cyanobacteria (blue-green algae) which occur in water bodies with high eutrophication especially those with a slow flow rate or those that are stagnant in warm climates. Mammalian exposure to these compounds has been associated with deleterious effects and in high dosage cases, deaths of animals has been reported. The metabolic profile of HepG2 cells is closely related to that of hepatocytes and therefore serves as a good model due to their human origin. Proton nuclear magnetic resonance spectroscopy (¹H NMR) and direct injection mass spectrometry (DIMS) were used to analyse media extracts from the cells and data obtained was reduced by chemometric methods. The use of principal component analysis (PCA) enabled achievement of a visual distinction between the metabolic profiles of samples exposed to microcystins, control samples (unexposed), and those which were exposed to acetaminophen (positive control). A profile of media components showed that some components in the samples exposed to microcystins increased compared to those in control samples. They included amino acids, organic acids, lipids, some purines and pyrimidines. In general exposure to low concentration of microcystin was found to interfere with amino acid metabolism, carbohydrate metabolism, lipid metabolism and nucleic acids metabolism. Furthermore, low concentration of microcystins did not result in significant cell death; rather the cells continued to proliferate.     

Temperature distribution in human skin and subdermal tissues

Temperature profiles have been computed in the skin and subdermal part of a human body for (i) various values of environmental temperature, rate of sweat evaporation and wind velocity, (ii) rate of blood mass flow, (iii) rate of metabolic heat generation and (iv) three different sets of thicknesses of skin layers. The mathematical equations have been considered for a one-dimensional steady-state case. The two important physical parameters, namely rate of blood mass flow and rate of metabolic heat generation, have been assigned position-dependent values. The latter is also taken as linearly dependent on the tissue temperature. Analytic solutions have been obtained for the three layers of the region. These forms of solution facilitate the study of parameter dependence.     

Physiological control of warming and cooling during simulated shuttling and basking in lizards

Differences in warming and cooling rates in basking lizards have long been thought to be brought about by adjustments in heart rate and blood flow. We examined the physiological control of warming and cooling in Iguana iguana, Sceloporus undulatus, and three species of Cordylus by measuring time constants, heart rate, and superficial capillary blood flow. Previously, techniques have not been available to measure time constants in shuttling animals. Using a combination of rapid measurements of temperature and blood flow and numerically intensive parameter-fitting methods, we measured dominant and subdominant time constants in lizards subjected to periods of both simulated basking and simulated shuttling. Cutaneous blood flow and heart rate were measured using laser Doppler flowmeters. Of the three, only the larger I. iguana measurably altered rates of warming and cooling during basking. During shuttling, none of the species effectively controlled warming and cooling. During both basking and shuttling, blood flow and heart rate tended to change in predicted directions. Superficial blood flow correlated with surface temperature while heart rate correlated more closely with core temperature. Changes in superficial blood flow and heart rate varied relatively independently in I. iguana. The techniques used here provide a better understanding of the ability of these species to control thermoregulation.     

Protein-Induced Membrane Curvature Alters Local Membrane Tension

Adsorption of proteins onto membranes can alter the local membrane curvature. This phenomenon has been observed in biological processes such as endocytosis, tubulation, and vesiculation. However, it is not clear how the local surface properties of the membrane, such as membrane tension, change in response to protein adsorption. In this article, we show that the partial differential equations arising from classical elastic model of lipid membranes, which account for simultaneous changes in shape and membrane tension due to protein adsorption in a local region, cannot be solved for nonaxisymmetric geometries using straightforward numerical techniques; instead, a viscous-elastic formulation is necessary to fully describe the system. Therefore, we develop a viscous-elastic model for inhomogeneous membranes of the Helfrich type. Using the newly available viscous-elastic model, we find that the lipids flow to accommodate changes in membrane curvature during protein adsorption. We show that, at the end of protein adsorption process, the system sustains a residual local tension to balance the difference between the actual mean curvature and the imposed spontaneous curvature. We also show that this change in membrane tension can have a functional impact such as altered response to pulling forces in the presence of proteins.     

Changes in cardiohemodynamic parameters,cardiointervalography, and microcirculation observed in local cold test in young men born in northern regions

The cardiohemodynamic and blood microcirculation parameters at rest and under local cold exposure in young male subjects have been estimated. It has been found that the subjects with the initially low velocity of erythrocytes (blood flow) in their nail bed capillaries have higher blood pressure, stroke volume, cardiac output, and cardiac index, which proves that these subjects have the hyperkinetic type of blood flow with the pronounced hypertensive reaction. At the same time, the shift of heart rate variability values under the cold exposure indicates that the activation of the sympathetic autonomic nervous system is more statistically significant than that in those subjects who originally had a higher velocity of erythrocytes. In the subjects of this group, no changes were observed in either heart rate autonomic regulation or index of tension under the local cold exposure, which proved that these subjects had the enhanced functional reserves of the cardiovascular system and autonomic regulation. They also had a fairly pronounced reactivity of the parameters of systemic hemodynamics, which manifested itself in changes in their blood filling parameters against the background of decrease in total peripheral vascular resistance and coefficient of integral tonicity.     

A study on the non-linear flow of blood through arteries

The pulsatile flow of blood through arteries is investigated in this paper by treating the blood vessel as a thin-walled anisotropic, non-linearly viscoelastic, incompressible circular cylindrical shell; nonlinearities of the flow of blood are also paid due consideration. The displacement components of the vessel wall are obtained from the equations of equilibrium which have been linearized by employing the principle of superimposition of a small deformation on a state of known finite deformation. The influence of the wall deformation on the flow properties of blood, has been accounted for by considering suitably formulated continuity conditions. A finitedifference scheme is employed for solving the flow equations together with the boundary and initial conditions by using the locally measured values of pressure and pressure gradient. Numerical results obtained for the velocity profile of blood flowing in a canine middle descending thoracic aorta have been presented through figures.