scholarly journals Relationships Between Lymphangiogenesis and Angiogenesis During Inflammation in Rat Mesentery Microvascular Networks

2012 ◽  
Vol 10 (4) ◽  
pp. 198-207 ◽  
Author(s):  
Richard S. Sweat ◽  
Peter C. Stapor ◽  
Walter L. Murfee
Keyword(s):  
Microvascular Networks ◽  
Rat Mesentery

A One-Dimensional Mathematical Model for Studying the Pulsatile Flow in Microvascular Networks

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Qing Pan ◽  
Ruofan Wang ◽  
Bettina Reglin ◽  
Guolong Cai ◽  
Jing Yan ◽  
...  
Keyword(s):  
Blood Flow ◽  
Pulsatility Index ◽  
Dynamic Models ◽  
Dynamic Properties ◽  
Microvascular Blood Flow ◽  
Integration Scheme ◽  
Microvascular Networks ◽  
Mean Values ◽  
One Dimensional ◽  
Rat Mesentery

Techniques that model microvascular hemodynamics have been developed for decades. While the physiological significance of pressure pulsatility is acknowledged, most of the microcirculatory models use steady flow approaches. To theoretically study the extent and transmission of pulsatility in microcirculation, dynamic models need to be developed. In this paper, we present a one-dimensional model to describe the dynamic behavior of microvascular blood flow. The model is applied to a microvascular network from a rat mesentery. Intravital microscopy was used to record the morphology and flow velocities in individual vessel segments, and boundaries are defined according to the experimental data. The system of governing equations constituting the model is solved numerically using the discontinuous Galerkin method. An implicit integration scheme is adopted to increase computing efficiency. The model allows the simulation of the dynamic properties of blood flow in microcirculatory networks, including the pressure pulsatility (quantified by a pulsatility index) and pulse wave velocity (PWV). From the main input arteriole to the main output venule, the pulsatility index decreases by 66.7%. PWV obtained along arterioles declines with decreasing diameters, with mean values of 77.16, 25.31, and 8.30 cm/s for diameters of 26.84, 17.46, and 13.33 μm, respectively. These results suggest that the 1D model developed is able to simulate the characteristics of pressure pulsatility and wave propagation in complex microvascular networks.

Relationship between structural and hemodynamic heterogeneity in microvascular networks

1996 ◽  
Vol 270 (2) ◽  
pp. H545-H553 ◽  
Author(s):  
A. R. Pries ◽  
T. W. Secomb ◽  
P. Gaehtgens
Keyword(s):  
Mathematical Model ◽  
Blood Flow ◽  
Topological Structure ◽  
Blood Rheology ◽  
Experimental Information ◽  
Microvascular Networks ◽  
Rat Mesentery ◽  
Hemodynamic Characteristics ◽  
Flow Through ◽  
The Relationship

The relationship between structural and hemodynamic heterogeneity of microvascular networks is examined by analyzing the effects of topological and geometric irregularities on network hemodynamics. Microscopic observations of a network in the rat mesentery provided data on length, diameter, and interconnection of all 913 segments. Two idealized network structures were derived from the observed network. In one, the topological structure was made symmetric; in another a further idealization was made by assigning equal lengths and diameters to all segments with topologically equivalent positions in the network. Blood flow through these three networks was simulated with a mathematical model based on experimental information on blood rheology. Overall network conductance and pressure distribution within the network were found to depend strongly on topological heterogeneity and less on geometric heterogeneity. In contrast, mean capillary hematocrit was sensitive to geometric heterogeneity but not to topological heterogeneity. Geometric and topological heterogeneity contributed equally to the dispersion of arteriovenous transit time. Hemodynamic characteristics of heterogeneous microvascular networks can only be adequately described if both topological and geometric variability in network structure are taken into account.

Structure and hemodynamics of microvascular networks: heterogeneity and correlations

1995 ◽  
Vol 269 (5) ◽  
pp. H1713-H1722 ◽  
Author(s):  
A. R. Pries ◽  
T. W. Secomb ◽  
P. Gaehtgens
Keyword(s):  
Vessel Diameter ◽  
Hemodynamic Parameters ◽  
Strong Correlations ◽  
Microvascular Networks ◽  
True Value ◽  
Rat Mesentery ◽  
Coefficients Of Variation ◽  
Network Properties ◽  
The Mean ◽  
Intravascular Pressure

The objective of this study was to quantify the heterogeneity of topological, morphological, and hemodynamic parameters in microvascular networks and to identify functionally relevant correlations among these parameters. Seven networks in the rat mesentery (383-913 vessel segments per network) were examined, and measurements were made of segment generation, diameter, length, and hematocrit in all segments (n = 3,129) and of flow velocity (only in 3 networks, 1,321 segments). In addition, hematocrit, flow rate, and pressure were derived for all segments from a mathematical simulation. All parameters obtained exhibit heterogeneous distributions with coefficients of variation ranging from 0.28 (capillary diameter) to > 1.5 (volume flow and pressure gradient). Several strong correlations exist between parameters, e.g., discharge hematocrit increases with vessel diameter, and shear rate increases with intravascular pressure. Because of such correlations, the extrapolation from average values for "typical vessels" to network properties can lead to substantial errors. For example, the mean network transit time estimated based on averaged quantities is 6.5 s, which is about 60% higher than the true value (4.08 s). Simplified models of the vascular bed may therefore be inadequate to describe functional properties of the microcirculation.

scholarly journals Structural adaptation and stability of microvascular networks: theory and simulations

1998 ◽  
Vol 275 (2) ◽  
pp. H349-H360 ◽  
Author(s):  
A. R. Pries ◽  
T. W. Secomb ◽  
P. Gaehtgens
Keyword(s):  
Network Flow ◽  
Equilibrium States ◽  
Structural Adaptation ◽  
Microvascular Networks ◽  
Vascular Walls ◽  
Rat Mesentery ◽  
Vascular Segment ◽  
Complete Networks ◽  
Intravascular Pressure

A theoretical model was developed to simulate long-term changes of vessel diameters during structural adaptation of microvascular networks in response to tissue needs. The diameter of each vascular segment was assumed to change with time in response to four local stimuli: endothelial wall shear stress (τw), intravascular pressure (P), a flow-dependent metabolic stimulus (M), and a stimulus conducted from distal to proximal segments along vascular walls (C). Increases in τw, M, or C or decreases in P were assumed to stimulate diameter increases. Hemodynamic quantities were estimated using a mathematical model of network flow. Simulations were continued until equilibrium states were reached in which the stimuli were in balance. Predictions were compared with data from intravital microscopy of the rat mesentery, including topological position, diameter, length, and flow velocity for each segment of complete networks. Stable equilibrium states, with realistic distributions of velocities and diameters, were achieved only when all four stimuli were included. According to the model, responses to τwand P ensure that diameters are smaller in peripheral than in proximal segments and are larger in venules than in corresponding arterioles, whereas M prevents collapse of networks to single pathways and C suppresses generation of large proximal shunts.

Structural adaptation of microvascular networks: functional roles of adaptive responses

2001 ◽  
Vol 281 (3) ◽  
pp. H1015-H1025 ◽  
Author(s):  
A. R. Pries ◽  
B. Reglin ◽  
T. W. Secomb
Keyword(s):  
Energy Dissipation ◽  
Metabolic Response ◽  
Threshold Level ◽  
Adaptive Responses ◽  
Structural Adaptation ◽  
Microvascular Networks ◽  
Reduced Pressure ◽  
Functional Roles ◽  
Network Characteristics ◽  
Rat Mesentery

Terminal vascular beds continually adapt to changing demands. A theoretical model is used to simulate structural diameter changes in response to hemodynamic and metabolic stimuli in microvascular networks. Increased wall shear stress and decreased intravascular pressure are assumed to stimulate diameter increase. Intravascular partial pressure of oxygen (Po2) is estimated for each segment. Decreasing Po2is assumed to generate a metabolic stimulus for diameter increase, which acts locally, upstream via conduction along vessel walls, and downstream via metabolite convection. By adjusting the sensitivities to these stimuli, good agreement is achieved between predicted network characteristics and experimental data from microvascular networks in rat mesentery. Reduced pressure sensitivity leads to increased capillary pressure with reduced viscous energy dissipation and little change in tissue oxygenation. Dissipation decreases strongly with decreased metabolic response. Below a threshold level of metabolic response flow shifts to shorter pathways through the network, and oxygen supply efficiency decreases sharply. In summary, the distribution of vessel diameters generated by the simulated adaptive process allows the network to meet the functional demands of tissue while avoiding excessive viscous energy dissipation.

scholarly journals Aging is associated with impaired angiogenesis, but normal microvascular network structure, in the rat mesentery

2017 ◽  
Vol 312 (2) ◽  
pp. H275-H284 ◽  
Author(s):  
Richard S. Sweat ◽  
David C. Sloas ◽  
Scott A. Stewart ◽  
Malwina Czarny-Ratajczak ◽  
Melody Baddoo ◽  
...  
Keyword(s):  
Endothelial Cell ◽  
Microvascular Dysfunction ◽  
Vessel Density ◽  
Rna Seq ◽  
Microvascular Networks ◽  
Fischer 344 ◽  
Rat Mesentery ◽  
Vascular Area ◽  
Platelet Endothelial Cell Adhesion ◽  
Impaired Angiogenesis

A big problem associated with aging is thought to be impaired microvascular growth or angiogenesis. However, to link the evidence for impaired angiogenesis to microvascular dysfunction in aged tissues, we must compare adult vs. aged microvascular networks in unstimulated scenarios. The objective of this study was to test the hypothesis that aged microvascular networks are characterized by both fewer vessels and the impaired ability to undergo angiogenesis. Mesentery tissues from adult (9-mo) and aged (24-mo) male Fischer 344 rats were harvested and immunolabeled for platelet/endothelial cell adhesion molecule (an endothelial cell marker) according to two scenarios: unstimulated and stimulated. For unstimulated groups, tissues harvested from adult and aged rats were compared. For stimulated groups, tissues were harvested 3 or 10 days after compound 48/80-induced mast cell degranulation stimulation. Unstimulated aged microvascular networks displayed larger mean vascular area per tissue area compared with the unstimulated adult networks. The lack of a decrease in vessel density was supported at the gene expression level with RNA-Seq analysis and with comparison of vessel densities in soleus muscle. Following stimulation, capillary sprouting and vessel density were impaired in aged networks at 3 and 10 days, respectively. Our results suggest that aging associated with impaired angiogenesis mechanisms might not influence normal microvascular function, since unstimulated aged microvascular networks can display a “normal adult-like” vessel density and architecture. NEW & NOTEWORTHY Using a multidimensional approach, we present evidence supporting that aged microvascular networks display vessel density and patterning similar to adult networks despite also being characterized by a decreased capacity to undergo angiogenesis. Thus, vessel loss is not necessarily a characteristic of aging.

Microvascular blood flow resistance: role of endothelial surface layer

1997 ◽  
Vol 273 (5) ◽  
pp. H2272-H2279 ◽  
Author(s):  
Axel R. Pries ◽  
Timothy W. Secomb ◽  
Helfried Jacobs ◽  
Markus Sperandio ◽  
Kurt Osterloh ◽  
...  
Keyword(s):  
Blood Flow ◽  
Flow Resistance ◽  
Capillary Flow ◽  
Vessel Diameter ◽  
Low Flow ◽  
Microvascular Blood Flow ◽  
Microvascular Networks ◽  
Flow Rates ◽  
Rat Mesentery ◽  
Endothelial Surface

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 ∼1 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 < 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.

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