Rauber's sickle and not the caudal marginal zone induces a primitive streak, blood vessels, blood cell formation and coelomic vesicles in avian blastoderms

By using the quail-chicken chimera technique, we studied the reactivity and the eventual developmental or inducing capacities of the avian caudal marginal zone (in comparison with Rauber's sickle), when associated in vitro with different avian blastoderm components. If a fragment of quail sickle endoblast is placed on the caudal marginal zone of a whole unincubated chicken blastoderm, then a secondary miniature embryo will develop in this caudal marginal zone. The primitive streak and accompanying neural plate of the secondary embryo are directed peripherally into the caudal germ wall, away from Rauber's sickle. Thus, the 'mirror image development' indicates that the upper layer of the caudal marginal zone can react in the same way as the upper layer of the area centralis, because of the presence of sickle endoblast. A quail Rauber's sickle fragment placed on an isolated anti-sickle region always induces a primitive streak directed centrally. After prolonged culture, blood vessels and associated coelomic vesicles are formed. By contrast if a quail caudal marginal zone is placed on an isolated chicken anti-sickle region, the primitive streak, blood vessels and coelomic vesicles do not form. Thus, in contrast to the inducing effect of Rauber's sickle, the caudal marginal zone has no inducing effect by itself, even in the absence of the dominating effect of Rauber's sickle.     

A semi-empirical model of apparent blood viscosity as a function of vessel diameter and discharge hematocrit

A semi-empirical model is developed to describe the dependence of apparent viscosity of blood on vessel diameter (2.7 to 500 microns) and vessel discharge hematocrit (5% to 60%). The blood flow is modeled as a cell-rich core and a cell-free marginal layer in the larger vessels and an axial-train in the smaller vessels. Laminar (Poiseuille) flow is assumed in all cases. An equation is derived in which apparent viscosity is a function of vessel diameter, core viscosity, and width of marginal layer. This is then complemented by empirical equations in which core viscosity varies exponentially with discharge hematocrit while the width of marginal layer varies linearly with discharge hematocrit. The model correlates well with several sets of experimental data and behaves according to the Fahraeus-Lindqvist effect. Predicted apparent viscosity tends to the expected finite value for large vessel diameters. Dependence of apparent viscosity on vessel diameter is realistically smooth in the whole diameter range.     

A semi-empirical model for flow of blood and other particulate suspensions through narrow tubes

A semi-empirical model applicable to the flow of blood and other particulate suspensions through narrow tubes has been developed. It envisages a central core of blood surrounded by a wall layer of reduced hematocrit. With the help of this model the wall layer thickness and extent of plug flow may be calculated using pressure drop, flow rate and hematocrit reduction data. It has been found from the available data in the literature that for a given sample of blood the extent of plug flow increases with decreasing tube diameter. Also for a flow through a given tube it increases with hematocrit. The wall layer thickness is found to decrease with increase in blood hematocrit. A comparison between the results of rigid particulate suspensions and blood reveals that the thicker wall layer and smaller plug flow radius in the case of blood may be attributed to the deformability of the erythrocytes.     

The effect of the external medium on the gravitropic curvature of rice (Oryza sativa, Poaceae) roots

The roots of rice seedlings, growing in artificial pond water, exhibit robust gravitropic curvature when placed perpendicular to the vector of gravity. To determine whether the statolith theory (in which intracellular sedimenting particles are responsible for gravity sensing) or the gravitational pressure theory (in which the entire protoplast acts as the gravity sensor) best accounts for gravity sensing in rice roots, we changed the physical properties of the external medium with impermeant solutes and examined the effect on gravitropism. As the density of the external medium is increased, the rate of gravitropic curvature decreases. The decrease in the rate of gravicurvature cannot be attributed to an inhibition of growth, since rice roots grown in 100 Osm/m3 (0.248 MPa) solutions of different densities all support the same root growth rate but inhibit gravicurvature increasingly with increasing density. By contrast, the sedimentation rate of amyloplasts in the columella cells is unaffected by the external density. These results are consistent with the gravitational pressure theory of gravity sensing, but cannot be explained by the statolith theory.     

The Diffusion of Oxygen, Carbon Dioxide, and Inert Gas in Flowing Blood

Measurements were made of exchange rates of oxygen, carbon dioxide, and krypton-85 with blood at 37.5°C. Gas transfer took place across a 1 mil silicone rubber membrane. The blood was in a rotating disk boundary layer flow, and the controlling resistance to transfer was the concentration boundary layer. Measured rates were compared with rates predicted from the equation of convective diffusion using velocities derived from the Navier-Stokes equations and diffusivities calculated from the theory for conduction in a heterogeneous medium. The measured absorption rate of krypton-85 was closely predicted by this model. Significant deposition of material onto the membrane surface, resulting in an increased transfer resistance, occurred in one experiment with blood previously used in a nonmembrane type artificial lung. The desorption rate of oxygen from blood at low P_o2¹ was up to four times the corresponding transfer rate of inert gas. This effect is described somewhat conservatively by a local equilibrium form of the convective diffusion equation. The carbon dioxide transfer rate in blood near venous conditions was about twice that of inert gas, a rate significantly greater than predicted by the local equilibrium theory. It should be possible to apply these theoretical methods to predict exchange rates with blood flowing in systems of other geometries.     

A numerical model for studying the effect of plasma layer on the process of blood oxygenation in the pulmonary capillaries

A two layer model for the blood oxygenation in pulmonary capillaries is proposed. The model consists of a core of erythrocytes surrounded by a symmetrically placed plasma layer. The governing equations in the core describe the free molecular diffusion, convection, and facilitated diffusion due to the presence of haemoglobin. The corresponding equations in the plasma layer are based on the free molecular diffusion and the convective effect of the blood. According to the axial train model for the blood flow proposed by Whitmore (1967), the core will move with a uniform velocity whereas flow in the plasma layer will be fully developed. The resulting system of nonlinear partial differential equations is solved numerically. A fixed point iterative technique is used to deal with the nonlinearities. The distance traversed by the blood before getting fully oxygenated is computed. It is shown that the concentration of O2 increases continuously along the length of the capillary for a given ratio of core radius to capillary radius. It is found that the rate of oxygenation increases as the core to capillary ratio decreases. The equilibration length increases with a heterogeneous model in comparison to that in a homogeneous model. The effect of capillary diameters and core radii on the rate of oxygenation has also been examined.     

A Mathematical Study on Three Layered Oscillatory Blood Flow Through Stenosed Arteries

A mathematical model is constructed to examine the characteristics of three layered blood flow through the oscillatory cylindrical tube (stenosed arteries).The proposed model basically consists three layers of blood (viscous fluids with different viscosities) named as core layer (red blood cells),intermediate layer (platelets/white blood cells) and peripheral layer (plasma).The analysis was restricted to propagation of small-amplitude harmonic waves,generated due to blood flow whose wave length is larger compared to the radius of the arterial segment.The impacts of viscosity of fluid in peripheral layer and intermediate layer on the interfaces,average flow rate,mechanical efficiency,trapping and reflux are discussed with the help of numerical and computational results.This model is the generalized form of the preceding models.On the basis of present discussion,it is found that the size of intermediate and peripheral layers reduces in expanded region and enhances in contracted region with the increasing viscosity of fluid in peripheral layer,whereas,opposite effect is observed for viscosity of fluid in intermediate layer.Final conclusion is that the average flow rate and mechanical efficiency increase with the increasing viscosity of fluid in both layers,however,the effects of the viscosity of fluid in both layers on trapping and reflux are opposite to each other.     

The interdependent contributions of gravitational and structural features to perfusion distribution in a multiscale model of the pulmonary circulation

Recent experimental and imaging studies suggest that the influence of gravity on the measured distribution of blood flow in the lung is largely through deformation of the parenchymal tissue. To study the contribution of hydrostatic effects to regional perfusion in the presence of tissue deformation, we have developed an anatomically structured computational model of the pulmonary circulation (arteries, capillaries, veins), coupled to a continuum model of tissue deformation, and including scale-appropriate fluid dynamics for blood flow in each vessel type. The model demonstrates that both structural and the multiple effects of gravity on the pulmonary circulation make a distinct contribution to the distribution of blood. It shows that postural differences in perfusion gradients can be explained by the combined effect of tissue deformation and extra-acinar blood vessel resistance to flow in the dependent tissue. However, gravitational perfusion gradients persist when the effect of tissue deformation is eliminated, highlighting the importance of the hydrostatic effects of gravity on blood distribution in the pulmonary circulation. Coupling of large- and small-scale models reveals variation in microcirculatory driving pressures within isogravitational planes due to extra-acinar vessel resistance. Variation in driving pressures is due to heterogeneous large-vessel resistance as a consequence of geometric asymmetry in the vascular trees and is amplified by the complex balance of pressures, distension, and flow at the microcirculatory level.     

Peristaltic transport of multilayered power-law fluids with distinct viscosities: a mathematical model for intestinal flows

This paper is concerned with the theoretical study of two-dimensional peristaltic flow of power-law fluids in three layers with different viscosities. The analysis is carried out under low Reynolds number and long wavelength approximations. The shapes of the interfaces are described by a system of non-linear algebraic equations which are solved numerically as streamlines. It is found that the non-uniformity in the intermediate and peripheral layers diminishes when the viscosity of the intermediate layer is increased and that of the outermost layer is kept unaltered for both the pseudo-plastic and dilatant fluids. Similar are the observations when the viscosity of the outermost layer is increased and that of the intermediate layer is kept fixed. The flow rate increases with the viscosities of the peripheral and the intermediate layers but the viscosity of the outermost layer is more effective. However, the knowledge of the effect of the viscosity of the intermediate layer facilitates us to achieve the required flow rate without disturbing the outermost layer. An increase in the flow behaviour index too favours larger flow rates. The trapping limits increase with the viscosity of the intermediate layer but decrease with the viscosity of the outermost layer and the flow behaviour index. Thus, a medicinal intervention that creates a more viscous intermediate layer and reduces pseudo plasticity may reduce constipation.     

The relationship of umbilical glucose uptake to uterine blood flow

In 30 experiments performed on 5 pregnant sheep, the rate of glucose transfer from the placenta to fetus via the umbilical circulation was measured while varying uterine blood flow by means of a cuff-type occluder and while maintaining a constant maternal glucose concentration by means of a 'glucose clamp'. Over the range of uterine blood flows obtained, there was no significant effect on the simultaneously measured umbilical blood flow. Fetal glucose uptake and arterial glucose concentration remained normal as the uterine blood flow rate decreased from 600 to 300 ml per min per kg of fetus. At blood flow rates less than 300 ml.min-1.kg-1, the fetal glucose uptake decreased and became negative in one instance while the arterial glucose concentration became variable and markedly increased in 2 animals. This increase in fetal glucose concentration was associated with a decrease in the uterine oxygen delivery rate, a decrease in fetal oxygen content and a decrease in fetal oxygen uptake. These observations support the concept that fetal glucose metabolism is altered by severe hypoxia and demonstrate that there is little effect of uterine blood flow on fetal glucose uptake in the normal physiological range.     

An analysis of the sluicing gate in pulmonary blood flow

For pulmonary blood flow in zone 2 condition, in which the blood pressure in the venule (pven) is lower than the alveolar gas pressure (pA), the blood exiting from the capillary sheet and entering a venule must go through a sluicing gate. The sluicing gate exists because the venule remains patent while the capillaries will collapse when the static pressure of blood falls below the alveolar gas pressure. In the original theory of sheet flow the effect of the tension in the interalveolar septa on the flow through the sluicing gate was ignored. Since the tension multiplied by the curvature of the membrane is equivalent to a lateral pressure tending to open the gate, and since the curvature of the capillary wall is high in the gate region, this effect may be important. The present analysis improves the original theory and demonstrates that the effect of membrane tension is to cause flow to increase when the venous pressure continues to decrease. The shape of the sluicing gate resembles that of a venturi tube, and can be determined by an iterative integration of the differential equations. The result forms an important link in the theory of pulmonary blood flow in zone 2 condition.     

重力对锥形血管中血流压力的影响——基于考虑体位改变的三维流固耦合数学模型

重力是体位改变过程中最基本的生物力学刺激因素．血流压力是表征心血管功能状态的一个基本指标．目前,体位改变影响心血管系统的确切内部机制尚不清楚．为此,采用在流体和固体方程中分别引入体力项的方法,建立一个基于血流动力学概念的三维流固耦合数学模型,用以研究体位改变,确切量化重力对血流压力的影响．通过数值计算,得到以下结果．水平卧位条件下：a．单一血管中血流压力由无重力影响的轴对称二维分布变为重力影响下的三维不对称分布;b．随着进出口压差由小变大,重力对压力分布和极值的影响由大变小,当压差值分别达到10 665.6 Pa(80 mmHg)和2 666.4 Pa(20 mmHg)时,重力的影响就不再随进出口压差增大而变化;对三维单一流体,重力影响的总体趋势类似．对正、倒直立位,压力均为二维轴对称分布,其重力影响强度约为水平卧位的2倍以上．结果表明：基于血流动力学概念,引入体力项,建立三维流固耦合模型为研究体位改变提供了一种新思路,重力对单一血管中血流压力分布和大小的影响因体位不同而不同,并与进出口压差密切相关,提示,若血管进出口压差较小,忽略重力影响,不考虑体位改变,以二维轴对称模型来研究血管中血流状态,须谨慎解释所得结果．     

Effect of intravenous eicosapentaenoic acid on cerebral blood flow, edema and brain prostaglandins in ischemic gerbils

Eicosapentaenoic acid is converted by cyclo-oxygenase to the prostacyclin, PGI3. Consequently eicosapentaenoic acid might protect the brain from the impairment in cerebral blood flow that follows temporary cerebral arterial occlusion. We studied the effect of 90% pure eicosapentaenoic acid, given intravenously, on cerebral blood flow, brain water and prostaglandins after ischemia in gerbils. Ischemia was produced by bilateral carotid occlusion for 15 min followed by reperfusion for 2 h. In experimental gerbils, 0.833 mg or 0.167 mg of eicosapentaenoic acid (Na salt) was given intravenously followed by a continuous infusion of 1 mg h-1. Control gerbils were given 0.167 mg of linoleic acid (Na salt) intravenously followed by a continuous infusion of 1 mg h-1 or a saline infusion. Regional cerebral blood flow was measured by the hydrogen clearance method and brain water by the specific gravity technique. Brain diene prostaglandins were measured by radioimmunoassay. In control gerbils cerebral blood flow decreased significantly during reperfusion and remained depressed after 2 h of reperfusion. In eicosapentaenoic acid treated gerbils blood flow decreased initially but after 2 h of reperfusion blood flow was significantly higher than in control gerbils. Brain edema and brain diene prostaglandins were not significantly different between control and experimental groups. Our study indicates that eicosapentaenoic acid, given intravenously, improves cerebral blood flow after ischemia and reperfusion. We speculate that this effect may be due to the formation of the prostacyclin, PGI3.     

The Effect of Shear Rate on the Molecular Mass Distribution of Heat-Induced Aggregates of Mixtures Containing Whey Proteins and κ-Carrageenan

The present study attempts to characterize the effect of shear rate on the composition, size, and molecular weight of the protein aggregates present in the upper layer after phase separation of 5% whey protein isolate (WPI) mixed with 0.5% κ-carrageenan (κ-car) at pH 7.0. The mixtures were heated and sheared under different shearing rates. Size exclusion chromatography (SEC), dynamic light scattering, and static light scattering were employed to describe the effect of shear rate on the size and molecular mass of WPI aggregates. At the molecular level, the size of the aggregates increased with an increase in shear rate. Shear rate also caused a decrease in turbidity of the upper layer after centrifugation. SEC combined with multi-angle laser light scattering showed that the WPI aggregates molecular mass was between 10⁶and 10⁷ g/mol when the shear rate increased from 3.6 to 86.4 s⁻¹. Two empirical models described well the effect of shear rate on the size of WPI aggregates, and both models gave comparable results. By varying process parameters such as flow behavior and temperature, it is possible to control WPI aggregation and, thus, obtain aggregates with a range of different characteristics (size).     

Effects of reducing uterine blood flow on fetal blood flow distribution and oxygen delivery.

We examined the effect of graded reduction in uterine blood flow on distribution of cardiac output and oxygen delivery to fetal organs and venous blood flow patterns in 9 fetal sheep using the radionuclide-labeled microsphere technique. We reduced uterine blood flow in two steps, decreasing fetal oxygen delivery to 70% and 50% of normal, and compared the results with those from a similar study from our laboratory on graded umbilical cord compression. With 50% reduction in fetal oxygen delivery, blood flow and the fraction of the cardiac output distributed to the brain, heart, and adrenal gland increased and that to the lungs, carcass, skin, and scalp decreased. Oxygen delivery to the brain and myocardium was maintained, while that to the adrenal doubled, and that to the brain stem increased transiently. The decrease in oxygen delivery to both carcass and lower body segment correlated linearly with oxygen consumption (P less than 0.001). The proportion of umbilical venous blood passing through the ductus venosus increased from 44.6% to 53% (P less than 0.05). The preferential distribution of ductus venosus blood flow through the foramen ovale to the heart and brain increased, but that to the upper carcass decreased so that ductus venosus-derived blood flow to the upper body did not change. Hence, the oxygen delivered to the brain from the ductus venosus was maintained, and that to the heart increased 54% even though ductus venosus-derived oxygen delivery to the upper body fell 34%. Abdominal inferior vena caval blood flow and its contribution to cardiac output decreased, but the proportion of the abdominal inferior vena caval blood distributed through the foramen ovale also increased from 23.0 to 30.9%. However, the actual amount of inferior vena caval blood passing through the foramen ovale did not change. There was a 70% fall in oxygen delivery to the upper body segment from the inferior vena cava. A greater portion of superior vena caval blood was also shunted through the foramen ovale to the upper body, but the actual amounts of blood and oxygen delivered to the upper body from this source were small. Thus, graded reduction of uterine blood flow causes a redistribution of fetal oxygen delivery and of venous flow patterns, which is clearly different from that observed previously during graded umbilical cord occlusion.     

The effects of erythrocythemia on blood viscosity,maximal systemic oxygen transport capacity and maximal rates of oxygen consumption in an amphibian

Graded erythrocythemia was induced by isovolemic loading of packed red blood cells in the toad, Bufo marinus. Blood viscosity, hematocrit, hemoglobin concentration, maximal aortic blood flow rate and maximal rates of oxygen consumption were determined after each load. Blood viscosity was related to hematocrit in the expected exponential manner; ln eta = 0.43 + 0.035 Hct. Maximal blood flow rates in the dorsal aorta were inversely proportional to blood viscosity and fit predictions of the Poiseuille-Hagen flow formula. The effect of increased blood viscosity was to reduce aortic pulse volume, but not maximal heart rate. Maximal systemic oxygen transport capacity (aortic blood flow rate X hemoglobin concentration X O2 binding capacity of hemoglobin) was linearly correlated with the maximal rate of oxygen consumption. These date indicate that optimal hematocrit theory is applicable for maximal blood flow rates in vivo, and that systemic oxygen transport is the primary limitation to aerial VO2 max in amphibians.     

Effect of blood viscosity on oxygen transport in residual stenosed artery following angioplasty

The effect of blood viscosity on oxygen transport in a stenosed coronary artery during the postangioplasty scenario is studied. In addition to incorporating varying blood viscosity using different hematocrit (Hct) concentrations, oxygen consumption by the avascular wall and its supply from vasa vasorum, nonlinear oxygen binding capacity of the hemoglobin, and basal to hyperemic flow rate changes are included in the calculation of oxygen transport in both the lumen and the avascular wall. The results of this study show that oxygen transport in the postangioplasty residual stenosed artery is affected by non-Newtonian shear-thinning property of the blood viscosity having variable Hct concentration. As Hct increases from 25% to 65%, the diminished recirculation zone for the increased Hct causes the commencement of pO(2) decrease to shift radially outward by approximately 20% from the center of the artery for the basal flow, but by approximately 10% for the hyperemic flow at the end of the diverging section. Oxygen concentration increases from a minimum value at the core of the recirculation zone to over 90 mm Hg before the lumen-wall interface at the diverging section for the hyperemic flow, which is attributed to increased shear rate and thinner lumen boundary layer for the hyperemic flow, and below 90 mm Hg for the basal flow. As Hct increases from 25% to 65%, the average of pO(2,min) beyond the diverging section drops by approximately 25% for the basal flow, whereas it increases by approximately 15% for the hyperemic flow. Thus, current results with the moderate stenosed artery indicate that reducing Hct might be favorable in terms of increasing O(2) flux and pO(2,min), in the medial region of the wall for the basal flow, while higher Hct is advantageous for the hyperemic flow beyond the diverging section. The results of this study not only provide significant details of oxygen transport under varying pathophysiologic blood conditions such as unusually high blood viscosity and flow rate, but might also be extended to offer implications for drug therapy related to blood-thinning medication and for blood transfusion and hemorrhage.     

Dynamics of blood flow: modeling of the Fåhræus–Lindqvist effect

To model the Fåhræus–Lindqvist effect, Haynes’ marginal zone theory is used, following previous works, i.e., a core layer of uniform red blood cells (RBCs) is assumed to be surrounded by an annular plasma layer in which no RBCs are present. A simplified trial-and-error solution procedure is provided to determine the size of the core region and the hematocrit level in that zone in addition to the apparent viscosity, given the (upstream) large vessel hematocrit level and the average hematocrit level in the (downstream) small vessel. To test the model, a set of experimental data is selected to provide not only apparent viscosity data but also the average hematocrit levels in small tubes of different diameters. The results are found to support Haynes’ marginal theory, with no fitting parameters used in the computations. Viscous dissipation is determined. The use of the mechanical energy balance is found to lead to results that are consistent with those based on the momentum balance, while leaving the average hematocrit level undetermined and required by either experimental data or an additional equation based on further theoretical work. The present analysis is used to model bifurcation using published empirical correlations quantifying the Fåhræus effect and phase separation. The model equations are extended to microvascular networks with repeated bifurcations.     

Effect of sympathetic stimulation on salivary secretion in submandibular gland in the rabbit stimulated by pilocarpine

The sympathetic stimulation under slow pilocarpine-induced flow conditions brought about a decrease in this flow rate that could be due to vasoconstriction, since such an effect was not observed after the administration of phentolamine (4 mg/kg i.v.). Contrariwise the injection of a beta-adrenergic blocking agent (propranolol 2-2.5 mg/kg i.v.) produced a decrease of the salivary flow rate that was even greater than in the control animals. These results suggest that the secretory effect in this gland and species is predominantly beta-adrenergic. The stated results are related to the changes observed in the blood outflow from the gland.     

血浆层对血管壁剪应力和剪应力梯度的影响

在细小血管中,由于血细胞明显的趋轴效应,管中的血液分为两个不同的区域,即具有血细胞的核心区和邻近管壁和血浆层。应用两相分层流模型,研究在相同的流量和管径下,当核心区中的血液分别为牛顿流体和Casson流体时,不同的血浆层厚度对细小血管壁剪应力和剪应力梯度的影响。结果表明,血浆层的存在对壁剪应力和壁剪应力梯度有较大影响,当血浆层厚度仅为血管半径的1％和3％时,壁剪应力梯度分别下降约10％和20％。