A Scaling Law of Vascular Volume

Vascular volume is of fundamental significance to the function of the cardiovascular system. An accurate prediction of blood volume in patients is physiologically and clinically significant. This study proposes what we believe is a novel volume scaling relation of the form: Vc=KvDs2/3Lc, where V_c and L_c are cumulative vessel volume and length, respectively, in the tree, and D_s is the diameter of the vessel segment. The scaling relation is validated in vascular trees of various organs including the heart, lung, mesentery, muscle, and eye of different species. Based on the minimum energy hypothesis and volume scaling relation, four structure-function scaling relations are predicted, including the diameter-length, volume-length, flow-diameter, and volume-diameter relations, with exponent values of 3/7, 127, 2⅓, and 3, respectively. These four relations are validated in the various vascular trees, which further confirm the volume scaling relation. This scaling relation may serve as a control reference to estimate the blood volume in various organs and species. The deviation from the scaling relation may indicate hypovolemia or hypervolemia and aid diagnosis.     

Fluid-Dynamic Optimal Design of Helical Vascular Graft for Stenotic Disturbed Flow

Although a helical configuration of a prosthetic vascular graft appears to be clinically beneficial in suppressing thrombosis and intimal hyperplasia, an optimization of a helical design has yet to be achieved because of the lack of a detailed understanding on hemodynamic features in helical grafts and their fluid dynamic influences. In the present study, the swirling flow in a helical graft was hypothesized to have beneficial influences on a disturbed flow structure such as stenotic flow. The characteristics of swirling flows generated by helical tubes with various helical pitches and curvatures were investigated to prove the hypothesis. The fluid dynamic influences of these helical tubes on stenotic flow were quantitatively analysed by using a particle image velocimetry technique. Results showed that the swirling intensity and helicity of the swirling flow have a linear relation with a modified Germano number (Gn*) of the helical pipe. In addition, the swirling flow generated a beneficial flow structure at the stenosis by reducing the size of the recirculation flow under steady and pulsatile flow conditions. Therefore, the beneficial effects of a helical graft on the flow field can be estimated by using the magnitude of Gn*. Finally, an optimized helical design with a maximum Gn* was suggested for the future design of a vascular graft.     

How Does Water Ascend in Tall Trees and Other Vascular Plants?

Since the Cohesion Theory was first introduced, a series ofincompatible observations has appeared in the literature. Directmeasurements of xylem pressure in single vessels of higher plantsand tall trees by means of the xylem pressure probe techniqueindicate that xylem tension in the leaves of intact, transpiringplants is often much smaller than that predicted for transpiration-drivenwater ascent through continuous water columns. We conclude thatthe available evidence warrants a critical reappraisal of tension-drivenwater transport as the exclusive mechanism of long-distancewater transport in plants.Copyright 1995, 1999 Academic Press Cohesion Theory, higher plants, long-distance transport, trees, water ascent, xylem pressure probe     

Vascular Development and Sap Flow in Apple Pedicels

Xylem and phloem tissues of the pedicel of apple fruit increasein cross-sectional area throughout development. The increasein phloem is similar in the two cultivars examined (Cox's OrangePippin and Royal Gala) and reflects a steadily increasing phloemsap flow to the fruit. The increase in xylem tissue is due toa proliferation of non-conducting, structural, components sinceclose examination reveals no increase in the number of vesselelements from just after flowering onwards. The greater number,and the larger diameter, of the vessels in Cox's explains theinitially higher xylem conductance found in this cultivar. In vitro measurements of xylem exudation reveal a decline duringthe growing season in the xylem conductance of both cultivarsand an increasing proportion of fruit (particularly in Cox's)in which the xylem comes to be totally non-conducting. Thisobservation is in line with previously reported measurementsof xylem sap flow in vivo. The straightforward techniques used in this study offer a feasiblealternative to more arduous methods of assessing xylem and phloemsap flows and their balance during growth.Copyright 1994, 1999Academic Press Apple, xylem, phloem, vascular development, sap flow, Malus domestica Borkh     

Trees for bees

Controversy over the origins and evolution of social behaviour in the major groups of social bees (the corbiculate bees) has fuelled arguments over different approaches for building evolutionary trees. However, the application of different analytical methodologies does not explain why molecular and morphological data suggest strikingly different hypotheses for the evolution of eusociality in bees. Determining the phylogenetic root is expected to help resolve the question of the social evolution of corbiculate bees. However, this requires that the long branch attraction problem is overcome. This phenomenon affects both molecular and morphological data for corbiculate bees.     

The Role of CaV2.1 Channel Facilitation in Synaptic Facilitation

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Evidence for Mass Flow in Flowering Individuals of the Submersed Vascular Plant Myriophyllum heterophyllum

Myriophyllum heterophyllum Michx. is a rhizomatous submersed aquatic plant that produces a short, emergent floral spike. We hypothesized that lacunar pressures in emergent spikes should be at or near atmospheric pressure and that a mass flow of gases from submersed stems through the rhizome to emergent stems may occur as lacunar O2 concentrations and pressures in submersed stems increase during photosynthesis. We examined the potential for a pressure gradient ([delta]P) to develop along this pathway by measuring diurnal changes in lacunar gas composition and pressure in submersed stems of nonflowering plants and emergent stems of flowering individuals. Methane release from emergent spikes was also monitored during three diurnal cycles to evaluate the hypothesis that the [delta]P is maintained by the release of lacunar gases to the atmosphere. Lacunar O2 concentrations and pressures in submersed stems increased at sunrise and reached maximum levels by midday. Although O2 fluctuated similarly in emergent stems, lacunar pressures remained at or near atmospheric pressure, indicating that a [delta]P is generated between submersed and emergent stems during photosynthesis. Methane release from emergent spikes increased as lacunar pressures increased, indicating that rhizome gases are transported through emergent stems by mass flow and the [delta]P is maintained by venting lacunar gases from emergent spikes. The potential for mass flow in both flowering and nonflowering individuals is discussed.     

Quantification of Blood Flow and Topology in Developing Vascular Networks

Since fluid dynamics plays a critical role in vascular remodeling, quantification of the hemodynamics is crucial to gain more insight into this complex process. Better understanding of vascular development can improve prediction of the process, and may eventually even be used to influence the vascular structure. In this study, a methodology to quantify hemodynamics and network structure of developing vascular networks is described. The hemodynamic parameters and topology are derived from detailed local blood flow velocities, obtained by in vivo micro-PIV measurements. The use of such detailed flow measurements is shown to be essential, as blood vessels with a similar diameter can have a large variation in flow rate. Measurements are performed in the yolk sacs of seven chicken embryos at two developmental stages between HH 13+ and 17+. A large range of flow velocities (1 µm/s to 1 mm/s) is measured in blood vessels with diameters in the range of 25–500 µm. The quality of the data sets is investigated by verifying the flow balances in the branching points. This shows that the quality of the data sets of the seven embryos is comparable for all stages observed, and the data is suitable for further analysis with known accuracy. When comparing two subsequently characterized networks of the same embryo, vascular remodeling is observed in all seven networks. However, the character of remodeling in the seven embryos differs and can be non-intuitive, which confirms the necessity of quantification. To illustrate the potential of the data, we present a preliminary quantitative study of key network topology parameters and we compare these with theoretical design rules.     

Impact of Elevated PCO2 on Mass Flow of Reduced Nitrogen in Trees

To analyze the effects of elevated carbon dioxide concentration （PCO2） on the mass flow of reduced nitro- gen （N） in the phloem and xylem of trees, juvenile beech （Fagus sylvatica L.） and spruce （Picea abies （L.） Karst.） were grown in phytotrons and exposed to ambient and elevated PCO2 （plus 687.5 mg/m^3 CO2） for three growing seasons. Elevated PCO2 significantly decreased the mass flow of N from the shoot to roots of beech by significantly reducing the concentration of soluble amino compounds in the phloem, even if the area of conductive phloem of cross-sectional bark tissue was significantly increased, because of less callus deposition in the sieve elements. In spruce, the downward mass flow of reduced N also tended to be decreased, similar to that in beech. Resembling findings in the phloem, N mass flow from roots to shoot in both tree species was significantly diminished owing to significantly reduced concentrations of amino compounds in the xylem and a lower transpiration rate. Therefore, the mass flow of reduced N between shoots and roots of trees was mainly governed by the concentrations of soluble amino compounds in the phloem and xylem in relation to the loading of reduced N in both long-distance transport pathways.     

Vascular Epiphytes on Isolated Pasture Trees Along a Rainfall Gradient in the Lowlands of Panama

Secondary habitats are increasing in importance in tropical countries due to ongoing destruction of pristine vegetation. In spite of the magnitude of current changes, our understanding of their effects on nontrees (e.g., nonvascular or vascular epiphytes) is still very patchy, particularly in lowland habitats. Here, we report a study with isolated pasture trees in southwest Panama. The >800 studied trees, which belonged to >100 different species, harbored almost 27,000 epiphytes of 83 species. Orchidaceae was the most species‐rich family, with almost 60 percent of all species, while Bromeliaceae were most abundant. A rainfall gradient in the study region from ca 1000 to >3000 mm explained more of the variation in species abundance and richness than host characteristics (e.g., species identity, tree size). The unexpectedly large number of epiphytes in these pastures still represents a substantial change relative to a natural setting, which is suggested by a comparison with a forest inventory under similar climatic conditions. In pastures, species richness was lower as deduced from individual‐based rarefaction curves, a larger proportion of species and individuals showed crassulacean acid metabolism, and the relationship of epiphyte abundance/species richness and tree diameter was much less steep. Even the already reduced diversity, however, may be only transient in secondary habitats—the long‐term persistence of epiphyte populations in pastures is an open question and has to be addressed by repeated monitoring to fully evaluate the significance of pasture trees for the conservation of vascular epiphytes in tropical lowlands.     

Spatial Scales of Pollen and Seed-Mediated Gene Flow in Tropical Rain Forest Trees

Gene flow via seed and pollen is a primary determinant of genetic and species diversity in plant communities at different spatial scales. This paper reviews studies of gene flow and population genetic structure in tropical rain forest trees and places them in ecological and biogeographic context. Although much pollination is among nearest neighbors, an increasing number of genetic studies report pollination ranging from 0.5–14 km for canopy tree species, resulting in extensive breeding areas in disturbed and undisturbed rain forest. Direct genetic measures of seed dispersal are still rare; however, studies of fine scale spatial genetic structure (SGS) indicate that the bulk of effective seed dispersal occurs at local scales, and we found no difference in SGS (Sp statistic) between temperate (N?=?24 species) and tropical forest trees (N?=?15). Our analysis did find significantly higher genetic differentiation in tropical trees (F _ST?=?0.177; N?=?42) than in temperate forest trees (F _ST?=?0.116; N?=?82). This may be due to the fact that tropical trees experience low but significant rates of self-fertilization and bi-parental inbreeding, whereas half of the temperate tree species in our survey are wind pollinated and are more strictly allogamous. Genetic drift may also be more pronounced in tropical trees due to the low population densities of most species.     

Flow Regulation in Coronary Vascular Tree: A Model Study

Background

Coronary blood flow can always be matched to the metabolic demand of the myocardium due to the regulation of vasoactive segments. Myocardial compressive forces play an important role in determining coronary blood flow but its impact on flow regulation is still unknown. The purpose of this study was to develop a coronary specified flow regulation model, which can integrate myocardial compressive forces and other identified regulation factors, to further investigate the coronary blood flow regulation behavior.

Method

A theoretical coronary flow regulation model including the myogenic, shear-dependent and metabolic responses was developed. Myocardial compressive forces were included in the modified wall tension model. Shear-dependent response was estimated by using the experimental data from coronary circulation. Capillary density and basal oxygen consumption were specified to corresponding to those in coronary circulation. Zero flow pressure was also modeled by using a simplified capillary model.

Result

Pressure-flow relations predicted by the proposed model are consistent with previous experimental data. The predicted diameter changes in small arteries are in good agreement with experiment observations in adenosine infusion and inhibition of NO synthesis conditions. Results demonstrate that the myocardial compressive forces acting on the vessel wall would extend the auto-regulatory range by decreasing the myogenic tone at the given perfusion pressure.

Conclusions

Myocardial compressive forces had great impact on coronary auto-regulation effect. The proposed model was proved to be consistent with experiment observations and can be employed to investigate the coronary blood flow regulation effect in physiological and pathophysiological conditions.     

Endothelial Cilia Mediate Low Flow Sensing during Zebrafish Vascular Development

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Inflow/Outflow Boundary Conditions for Particle-Based Blood Flow Simulations: Application to Arterial Bifurcations and Trees

When blood flows through a bifurcation, red blood cells (RBCs) travel into side branches at different hematocrit levels, and it is even possible that all RBCs enter into one branch only, leading to a complete separation of plasma and RBCs. To quantify this phenomenon via particle-based mesoscopic simulations, we developed a general framework for open boundary conditions in multiphase flows that is effective even for high hematocrit levels. The inflow at the inlet is duplicated from a fully developed flow generated in a pilot simulation with periodic boundary conditions. The outflow is controlled by adaptive forces to maintain the flow rate and velocity gradient at fixed values, while the particles leaving the arteriole at the outlet are removed from the system. Upon validation of this approach, we performed systematic 3D simulations to study plasma skimming in arterioles of diameters 20 to 32 microns. For a flow rate ratio 6:1 at the branches, we observed the “all-or-nothing” phenomenon with plasma only entering the low flow rate branch. We then simulated blood-plasma separation in arteriolar bifurcations with different bifurcation angles and same diameter of the daughter branches. Our simulations predict a significant increase in RBC flux through the main daughter branch as the bifurcation angle is increased. Finally, we demonstrated the effectiveness of the new methodology in simulations of blood flow in vessels with multiple inlets and outlets, constructed using an angiogenesis model.     

Flow Cytometric Analysis of Conidia of Fungi Isolated from Soybean Vascular Tissue

Flow cytometry was used to characterize isolates of Phialophora gregata using the fluorescence intensity of propidium iodide-stained conidia. The isolates differed in their mean fluorescence intensity, ranging from 100.0 to 129.7 arbitrary units (AU). When the number of fluorescent events was plotted against intensity of fluorescence, a single peak was observed. Fluorescent patterns of Acremonium isolates from soybean vascular tissue were compared with those of P. gregata. Their mean fluorescence intensity ranged from 76.4 to 88.0 AU. With some of these isolates, multiple peak histograms were observed, corresponding to multiple spore sizes as well as single and double nucleated conidia. Using flow cytometry, we were able to distinguish P. gregata isolates from those of Acremonium , based on mean fluorescence intensity and/or the presence of multiple peaks. Flow cytometric analysis of propidium-iodide stained conidia of Phialophora isolates should prove to be useful for determining the relative DNA content of different isolates collected from different geographic areas.     

应用Granier热消散探针（TDP）法测定树木的木质部液流：理论与实践

Granier热消散探针法是目前研究树木生理生态和森林水文最常用的测定整树水分利用的方法之一。然而,已有的相关综述文献中,还没有专门介绍利用Granier热消散探针研究木质部液流的综述文章。本文重点介绍了Granier热消散探针测定系统的理论基础,对有关该探针的校准和改进的最新研究进展进行了综述,并还深入探讨了零液流信号值的确定、自然热梯度、损伤效应、液流的逆格型和将木质部液流密度外推至整树蒸腾耗水量等重要的实际问题。     

应用Granier热消散探针(TDP)法测定树木的木质部液流:理论与实践

Granier热消散探针法是目前研究树木生理生态和森林水文最常用的测定整树水分利用的方法之一.然而,已有的相关综述文献中,还没有专门介绍利用Granier热消散探针研究木质部液流的综述文章.本文重点介绍了Granier热消散探针测定系统的理论基础,对有关该探针的校准和改进的最新研究进展进行了综述,并还深入探讨了零液流信号值的确定、自然热梯度、损伤效应、液流的逆格型和将木质部液流密度外推至整树蒸腾耗水量等重要的实际问题.     

New Genes for Old Trees

In addition to the extensive improvement programmes within fruitorchards and forest stands, considerable momentum is being generatedin the application of genetic manipulation strategies to a varietyof woody species. Several transformation approaches have beenadopted for the production of transgenic trees. These includeAgrobacterium-mediated gene delivery, chemical and/or electricalstimulated uptake of DNA into protoplasts, and the use of thenewer technology of high velocity bombardment of plant tissueswith DNA-coated particles. Transformation offers advantagesover other genetic manipulation techniques, such as somatichybridization, in that it allows the directed improvement oftrees with minimum disruption of the genetic integrity of anelite genome. The information presented here is a comprehensivereview of transformation in woody plants. Many of the advanceshave been made in this area during the last five years. Key words: Woody species, transformation, Agrobacterium, direct gene transfer     

Kynurenic Acid Triggers Firm Arrest of Leukocytes to Vascular Endothelium under Flow Conditions

Recent studies have demonstrated that kynurenic acid (KYNA), a compound produced endogenously by the interferon-γ-induced degradation of tryptophan by indoleamine 2,3-dioxygenase, activates the previously orphaned G protein-coupled receptor, GPR35. This receptor is expressed in immune tissues, although its potential function in immunomodulation remains to be explored. We determined that GPR35 was most highly expressed on human peripheral monocytes. In an in vitro vascular flow model, KYNA triggered the firm arrest of monocytes to both fibronectin and ICAM-1, via β₁ integrin- and β₂ integrin-mediated mechanisms, respectively. Incubation of monocytes with pertussis toxin prior to use in flow experiments significantly reduced the KYNA-induced monocyte adhesion, suggesting that adhesion is triggered by a G_i-mediated process. Furthermore, KYNA-triggered adhesion of monocytic cells was reduced by short hairpin RNA-mediated silencing of GPR35. Although GPR35 is expressed at slightly lower levels on neutrophils, KYNA induced firm adhesion of these cells to an ICAM-1-expressing monolayer as well. KYNA also elicited neutrophil shedding of surface L-selectin, another indicator of leukocyte activation. Taken together, these data suggest that KYNA could be an important early mediator of leukocyte recruitment.Leukocyte recruitment into tissue compartments is a tightly regulated process orchestrated by chemokines (1). Chemokines convert leukocyte rolling or tethering on the vascular endothelium to firm arrest via the activation of leukocyte surface integrins (2, 3). As chemoattractants, chemokines subsequently play an important role in the directional migration of leukocytes through tissues.Chemoattractant receptors are a subtype of G protein-coupled receptors (GPCRs),³ one of the largest known families of human proteins. Chemoattractant receptors bind a variety of agonists, including proteins such as interleukin-8 (IL-8, CXCL8) (4) and monocyte chemoattractant protein-1 (MCP-1, CCL2) (5), small peptides such as fMLP (6), as well as bioactive lipids including leukotriene B₄ (7). As such, chemoattractant receptors mirror the entire family of GPCRs, which can be activated by ligands ranging in size from metabolites to large proteins (8).Because GPCRs serve as targets for therapeutic intervention, considerable activity has gone into the identification of both putative GPCR genes and the ligands for the resulting receptors (8). Recently, the tryptophan metabolite kynurenic acid (KYNA) was identified as an agonist for the previously “orphaned” receptor GPR35. KYNA was shown to elicit intracellular release of Ca²⁺ in Chinese hamster ovary cells in which GPR35 was co-expressed in the context of a chimeric G protein signaling apparatus. HEK93 cells transfected with GPR35 and G_qo proteins accumulated inositol phosphate upon exposure to KYNA. KYNA also induced internalization of GPR35 on HeLa cells, which is commonly seen following the activation of GPRs with agonists such as chemokines (9).KYNA is produced endogenously as a result of the degradation of tryptophan (Fig. 1). In most tissues, the rate-limiting step in this degradation is the conversion of tryptophan to N-formylkynurenine, a reaction that can be catalyzed by the inducible enzyme indolemine 2,3-dioxygenase (IDO). IDO is induced by interferon-γ, which leads to a substantial increase in the concentration of KYNA and other tryptophan catabolites during inflammatory processes.Open in a separate windowFIGURE 1.Tryptophan catabolism pathway. Schematic diagram of tryptophan catabolism. Tryptophan is converted to N-formylkynurenine by IDO, and is then deformylated to form kynurenine. Kynurenine can be converted to kynurenic acid via kynurenine aminotransferases I and II (KAT), or converted via alternative pathways to anthranilic acid or quinolinic acid, a NAD precursor.Previous work has demonstrated that KYNA acts as a neuroprotective agent by antagonizing both N-methyl-d-aspartate and α7-nicotinic receptors (10–12). Many peripheral tissues, including the heart and vasculature, are also capable of generating KYNA (13, 14), although its role in these tissues has not been well defined. Expression analysis indicates that GPR35 is selectively present in immune and intestinal tissues. From a functional perspective, KYNA treatment inhibited the secretion of tumor necrosis factor-α by mononuclear cells treated with lipopolysaccharide (9). This finding is in general agreement with the prevailing literature suggesting that IDO-mediated tryptophan catabolism appears to play a significant counter-regulatory role in dampening down the activation of the immune system (15). However, the potential spectrum of physiological roles for KYNA in immune modulation remains incompletely characterized.Given the reported high level of GPR35 expression on circulating leukocytes, here we tested the hypothesis that KYNA may play a chemokine-like role in modulating leukocyte-endothelial interactions under physiologically relevant flow conditions as seen in the vasculature. We explored the intracellular signaling pathways by which KYNA may be activating leukocytes, as well as the surface integrins modulating these effects. We report the unanticipated finding that KYNA is sufficient to drive early leukocyte adhesion.