Flow across microvessel walls through the endothelial surface glycocalyx and the interendothelial cleft (original) (raw)
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Physiological Reviews, 1999
This review addresses classical questions concerning microvascular permeabiltiy in the light of recent experimental work on intact microvascular beds, single perfused microvessels, and endothelial cell cultures. Analyses, based on ultrastructural data from serial sections of the clefts between the endothelial cells of microvessels with continuous walls, conform to the hypothesis that different permeabilities to water and small hydrophilic solutes in microvessels of different tissues can be accounted for by tortuous three-dimensional pathways that pass through breaks in the junctional strands. A fiber matrix ultrafilter at the luminal entrance to the clefts is essential if microvascular walls are to retain their low permeability to macromolecules. Quantitative estimates of exchange through the channels in the endothelial cell membranes suggest that these contribute little to the permeability of most but not all microvessels. The arguments against the convective transport of macromole...
Pfl�gers Archiv - European Journal of Physiology, 1971
The distensibility characteristics of arterial microvessels were measured in isolated and perfused segments of canine mesenteric membrane. Pressure-diameter-relations were found to be concave to the pressure axis with a plateau of unchanging diameter seen in approximately 500/0 of the vessels at pressures above 70 mm ttg. The total change of diameter averaged approximately 15~ over the pressure range between 0 and 170 mm Hg. Changes of vessel length (on average 15~ were observed in those vessels which were not fixed at their maximum length by the surrounding connective tissue fibres. A correlation was found between the changes in length and the changes in diameter, indicating that both are influenced by the mechanical properties and the tension in the extravascular structures. The modulus of volume elasticity of arterial microvesscls not fixed at constant length was found to increase with increasing pressure, reaching values of approximately 1.0 9 106 dynes/cm ~ at a perfusion pressure of 100 mg Hg; for vessels with constant length values of up to 4.0 9 106 dynes/cm 2 were obtained. It is concluded that the peripheral microvessels exhibit a greater stiffness than larger arteries and in part derive their mechanical properties from the properties of the surrounding tissues.
Resistance to blood flow in microvessels in vivo
Circulation Research, 1994
Resistance to blood flow through peripheral vascular beds strongly influences cardiovascular function and transport to tissue. For a given vascular architecture, flow resistance is determined by the rheological behavior of blood flowing through microvessels. A new approach for calculating the contribution of blood rheology to microvascular flow resistance is presented. Morphology (diameter and length), flow velocity, hematocrit, and topological position were determined for all vessel segments (up to 913) of terminal microcirculatory networks in the rat mesentery by intravital microscopy. Flow velocity and hematocrit were also predicted from mathematical flow simulations, in which the assumed dependence of flow resistance on diameter, hematocrit, and shear rate was optimized to minimize the deviation between measured and predicted values. For microvessels with diameters below approximately 40 microns, the resulting flow resistances are markedly higher and show a stronger dependence o...
Journal of Biomechanical Engineering, 2004
Endothelial surface glycocalyx plays an important role in the regulation of microvessel permeability by possibly changing its charge and configuration. To investigate the mechanisms by which surface properties of the endothelial cells control the changes in microvessel permeability, we extended the electrodiffusion model developed by Fu et al. [Am. J. Physiol. 284, H1240–1250 (2003)], which is for the interendothelial cleft with a negatively charged surface glycocalyx layer, to include the filtration due to hydrostatic and oncotic pressures across the microvessel wall as well as the electrical potential across the glycocalyx layer. On the basis of the hypotheses proposed by Curry [Microcirculation 1(1): 11–26 (1994)], the predictions from this electrodiffusion-filtration model provide a good agreement with experimental data for permeability of negatively charged α-lactalbumin summarized in Curry [Microcirculation 1(1), 11–26 (1994)] under various conditions. In addition, we applied ...
Microvascular blood flow resistance: role of endothelial surface layer
American Journal of …, 1997
Observations of blood flow in microvascular networks have shown that the resistance to blood flow is about twice that expected from studies using narrow glass tubes. The goal of the present study was to test the hypothesis that a macromolecular layer (glycocalyx) lining the endothelial surface contributes to blood flow resistance. Changes in flow resistance in microvascular networks of the rat mesentery were observed with microinfusion of enzymes targeted at oligosaccharide side chains in the glycocalyx. Infusion of heparinase resulted in a sustained decrease in estimated flow resistance of 14-21%, hydrodynamically equivalent to a uniform increase of vessel diameter by ϳ1 µm. Infusion of neuraminidase led to accumulation of platelets on the endothelium and doubled flow resistance. Additional experiments in untreated vascular networks in which microvascular blood flow was reduced by partial microocclusion of the feeding arteriole showed a substantial increase of flow resistance at low flow rates (average capillary flow velocities Ͻ 100 diameters/s). These observations indicate that the glycocalyx has significant hemodynamic relevance that may increase at low flow rates, possibly because of a shear-dependent variation in glycocalyx thickness.
Biophysical aspects of blood flow in the microvasculature
Cardiovascular Research, 1996
The main function of the microvasculature is transport of materials. Water and solutes are carried by blood through the microvessels and exchanged, through vessel walls, with the surrounding tissues. This transport function is highly dependent on the architecture of the microvasculature and on the biophysical behavior of blood flowing through it. For example, the hydrodynamic resistance of a microvascular network, which determines the overall blood flow for a given perfusion pressure, depends on the number, size and arrangement of microvessels, the passive and active mechanisms governing their diameters, and on the apparent viscosity of blood flowing in them. Suspended elements in blood, especially red blood cells, strongly influence the apparent viscosity, which varies with several factors, including vessel diameter, hematocrit and blood flow velocity. The distribution of blood flows and red cell fluxes within a network, which influences the spatial pattern of mass transport, is determined by the mechanics of red cell motion in individual diverging bifurcations. Here, our current understanding of the biophysical processes governing blood flow in the microvasculature is reviewed, and some directions for future research are indicated.
Mechanotransduction and flow across the endothelial glycocalyx
Proceedings of the …, 2003
In this inaugural paper, we shall provide an overview of the endothelial surface layer or glycocalyx in several roles: as a transport barrier, as a porous hydrodynamic interface in the motion of red and white cells in microvessels, and as a mechanotransducer of fluid shearing stresses to the actin cortical cytoskeleton of the endothelial cell. These functions will be examined from a new perspective, the quasiperiodic ultrastructural model proposed in Squire et al. [Squire, J. M., Chew, M., Nneji, G., Neal, C., Barry, J. & Michel, C. (2001) J. Struct. for the 3D organization of the endothelial surface layer and its linkage to the submembranous scaffold. We shall show that the core proteins in the bush-like structures comprising the matrix have a flexural rigidity, EI, that is sufficiently stiff to serve as a molecular filter for plasma proteins and as an exquisitely designed transducer of fluid shearing stresses. However, EI is inadequate to prevent the buckling of these protein structures during the intermittent motion of red cells or the penetration of white cell microvilli. In these cellular interactions, the viscous draining resistance of the matrix is essential for preventing adhesive molecular interactions between proteins in the endothelial membrane and circulating cellular components.
An in Vitro Model for Endothelial Permeability: Assessment of
1995
SUMMARY An essential component of any in vitro model for endothelial permeability is a confluent cell monolayer. The model reported here utilizes primary human umbilical vein endothelial cells (HUVEC) cultured on recently developed polyethylene terephthalate micropore membranes. Using a modification of the Wright-Giemsa stain, confluent HUVEC monolayers grown on micropore membranes were routinely assessed using light microscopy. Determination of confluence using this method was confirmed by scanning electron microscopy. Transendothelial electrical resistance of HUVEC monolayers averaged 27.9 ? 11.4 n ? cm2, 10 to 21% higher than literature values. Studies characterizing the permeability of the endothelial cell monolayer to 3H-inulin demonstrated a linear relationship between the luminal concentration of 3H-inulin and its flux across HUVEC monolayers. The slope of the flux versus concentration plot, which represents endothelial clearance of 3Hinulin, was 2.01 ? 0.076 X 10-4 ml/min (r...