Diameter and blood flow of skeletal muscle venules during local flow regulation

1986 ◽  
Vol 250 (5) ◽  
pp. H828-H837 ◽  
Author(s):  
S. D. House ◽  
P. C. Johnson
Keyword(s):  
Skeletal Muscle ◽  
Blood Flow ◽  
Arterial Pressure ◽  
Blood Viscosity ◽  
Vessel Diameter ◽  
Sartorius Muscle ◽  
Viscosity Data ◽  
Pressure Reduction ◽  
Local Flow

Whole organ studies suggest that venous resistance increases as blood flow falls and decreases when blood flow increases. In experiments on skeletal muscle we tested the hypotheses that these resistance changes may be due to changes in venous diameter, changes in the number of venules with blood flow, and/or changes in the shear rate of blood in venules. The hypotheses were tested by measuring diameter and red cell velocity in cat sartorius muscle venules (7–200 microns diam) during arterial pressure reduction and muscle contraction. There was no observable change in venular diameter and an insignificant change in the number of venules with blood flow during these perturbations. There was a significant decrease in the normalized velocity (bulk velocity/vessel diameter) of blood from a mean of 13 s-1 under control conditions to 5 s-1 during arterial pressure reduction to 20 mmHg. Combining these blood velocity data with published in vivo viscosity data, it is deduced that apparent blood viscosity in venules would increase 100% when blood flow was reduced 60%. During postcontraction hyperemia the normalized velocity of blood in venules increased from 16 to 38 s-1, suggesting that apparent blood viscosity in venules would fall 54%.

Microvascular pressure in venules of skeletal muscle during arterial pressure reduction

1986 ◽  
Vol 250 (5) ◽  
pp. H838-H845 ◽  
Author(s):  
S. D. House ◽  
P. C. Johnson
Keyword(s):  
Skeletal Muscle ◽  
Blood Flow ◽  
Arterial Pressure ◽  
Pressure Gradient ◽  
Pressure Difference ◽  
Reactive Hyperemia ◽  
Sartorius Muscle ◽  
Pressure Reduction ◽  
Large Vein ◽  
The Difference

It has been suggested from whole organ studies that the viscosity of blood in skeletal muscle venules varies inversely with flow over physiological flow ranges. If this is the case, the hydrostatic pressure gradient in venules should change less than flow as flow is altered. To test this hypothesis, pressure in venules of cat sartorius muscle was measured during stepwise arterial pressure reduction to 20 mmHg. Large vein pressure remained constant at about 5 mmHg. Average pressures in the large venules (40–185 microns) ranged from 13.6 to 10.0 mmHg. The difference between pressure in these venules and large vein pressure fell in proportion to the reduction in blood pressure and blood flow. Pressures in the smallest venules studied (25 microns) averaged 19.7 +/- 6.2 (SD) mmHg. The pressure difference between the smallest venules and the large vein fell less than the arteriovenous pressure difference or blood flow when arterial pressure was reduced. During reactive hyperemia the pressure gradient between the smallest venules and the large vein rose proportionately less than blood flow. The stability of pressure in the smallest venules is consistent with the hypothesis that blood viscosity varies inversely with flow rate.

scholarly journals Microvascular blood viscosity in vivo and the endothelial surface layer

2005 ◽  
Vol 289 (6) ◽  
pp. H2657-H2664 ◽  
Author(s):  
A. R. Pries ◽  
T. W. Secomb
Keyword(s):  
Surface Layer ◽  
Blood Viscosity ◽  
Flow Resistance ◽  
Vessel Diameter ◽  
Viscosity Data ◽  
Endothelial Surface Layer ◽  
Rat Mesentery ◽  
Endothelial Surface

The apparent viscosity of blood in glass tubes declines with decreasing diameter (Fåhraeus-Lindqvist effect) and exhibits a distinctive minimum at 6–7 μm. However, flow resistance in vivo in small vessels is substantially higher than predicted by in vitro viscosity data. The presence of a thick endothelial surface layer (ESL) has been proposed as the primary cause for this discrepancy. Here, a physical model is proposed for microvascular flow resistance as a function of vessel diameter and hematocrit in vivo; it combines in vitro blood viscosity with effects of a diameter-dependent ESL. The model was developed on the basis of flow distributions observed in three microvascular networks in the rat mesentery with 392, 546, and 383 vessel segments, for which vessel diameters, network architecture, flow velocity, and hematocrit were determined by intravital microscopy. A previously described hemodynamic simulation was used to predict the distributions of flow and hematocrit from the assumed model for effective blood viscosity. The dependence of ESL thickness on vessel diameter was estimated by minimizing deviations of predicted values for velocities, flow directions, and hematocrits from measured data. Optimal results were obtained with a layer thickness of ∼0.8–1 μm for 10- to 40-μm-diameter vessels and declined strongly for smaller diameters, with an additional hematocrit-dependent impact on flow resistance exhibiting a maximum for ∼10-μm-diameter vessels. These results show that flow resistance in vivo can be explained by in vitro blood viscosity and the presence of an ESL and indicate the rheologically effective thickness of the ESL in microvessels.

Pulsatile Pressure and Flow in the Skeletal Muscle Microcirculation

1990 ◽  
Vol 112 (4) ◽  
pp. 437-443 ◽  
Author(s):  
Shou-Yan Lee ◽  
G. W. Schmid-Scho¨nbein
Keyword(s):  
Skeletal Muscle ◽  
Arterial Pressure ◽  
Time Course ◽  
Venous Pressure ◽  
Time Dependent ◽  
Physiological Importance ◽  
Pulsatile Pressure ◽  
Theoretical Predictions ◽  
Skeletal Muscle Microcirculation

Although blood flow in the microcirculation of the rat skeletal muscle has negligible inertia forces with very low Reynolds number and Womersley parameter, time-dependent pressure and flow variations can be observed. Such phenomena include, for example, arterial flow overshoot following a step arterial pressure, a gradual arterial pressure reduction for a step flow, or hysteresis between pressure and flow when a pulsatile pressure is applied. Arterial and venous flows do not follow the same time course during such transients. A theoretical analysis is presented for these phenomena using a microvessel with distensible viscoelastic walls and purely viscous flow subject to time variant arterial pressures. The results indicate that the vessel distensibility plays an important role in such time-dependent microvascular flow and the effects are of central physiological importance during normal muscle perfusion. In-vivo whole organ pressure-flow data in the dilated rat gracilis muscle agree in the time course with the theoretical predictions. Hemodynamic impedances of the skeletal muscle microcirculation are investigated for small arterial and venous pressure amplitudes superimposed on an initial steady flow and pressure drop along the vessel.

scholarly journals Effects of aging and exercise training on spinotrapezius muscle microvascular Po2 dynamics and vasomotor control

2011 ◽  
Vol 110 (3) ◽  
pp. 695-704 ◽  
Author(s):  
Danielle J. McCullough ◽  
Robert T. Davis ◽  
James M. Dominguez ◽  
John N. Stabley ◽  
Christian S. Bruells ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Blood Flow ◽  
Exercise Training ◽  
Sodium Nitroprusside ◽  
Vascular Function ◽  
Treadmill Running ◽  
Aged Rats ◽  
Phosphorescence Quenching

With advancing age, there is a reduction in exercise tolerance, resulting, in part, from a perturbed ability to match O2 delivery to uptake within skeletal muscle. In the spinotrapezius muscle (which is not recruited during incline treadmill running) of aged rats, we tested the hypotheses that exercise training will 1) improve the matching of O2 delivery to O2 uptake, evidenced through improved microvascular Po2 (PmO2), at rest and throughout the contractions transient; and 2) enhance endothelium-dependent vasodilation in first-order arterioles. Young (Y, ∼6 mo) and aged (O, >24 mo) Fischer 344 rats were assigned to control sedentary (YSED; n = 16, and OSED; n = 15) or exercise-trained (YET; n = 14, and OET; n = 13) groups. Spinotrapezius blood flow (via radiolabeled microspheres) was measured at rest and during exercise. Phosphorescence quenching was used to quantify PmO2 in vivo at rest and across the rest-to-twitch contraction (1 Hz, 5 min) transition in the spinotrapezius muscle. In a follow-up study, vasomotor responses to endothelium-dependent (acetylcholine) and -independent (sodium nitroprusside) stimuli were investigated in vitro. Blood flow to the spinotrapezius did not increase above resting values during exercise in either young or aged groups. Exercise training increased the precontraction baseline PmO2 (OET 37.5 ± 3.9 vs. OSED 24.7 ± 3.6 Torr, P < 0.05); the end-contracting PmO2 and the time-delay before PmO2 fell in the aged group but did not affect these values in the young. Exercise training improved maximal vasodilation in aged rats to acetylcholine (OET 62 ± 16 vs. OSED 27 ± 16%) and to sodium nitroprusside in both young and aged rats. Endurance training of aged rats enhances the PmO2 in a nonrecruited skeletal muscle and is associated with improved vascular smooth muscle function. These data support the notion that improvements in vascular function with exercise training are not isolated to the recruited muscle.

scholarly journals Microdialysis of skeletal muscle at rest

1999 ◽  
Vol 58 (4) ◽  
pp. 919-923 ◽  
Author(s):  
Jan Henriksson
Keyword(s):  
Skeletal Muscle ◽  
Blood Flow ◽  
Human Skeletal Muscle ◽  
Human Metabolism ◽  
High Expectations ◽  
Perfusate Flow ◽  
Muscle Research ◽  
Interstitial Glucose

Techniques in human skeletal muscle research are by necessity predominantly 'descriptive'.Microdialysis has raised high expectations that it could meet the demand for a method that allows 'mechanistic' investigations to be performed in human skeletal muscle. In the present review, some views are given on how well the initial expectations on the use of the microdialysis technique in skeletal muscle have been fulfilled, and the areas in which additional work is needed in order to validate microdialysis as an important metabolic technique in this tissue. The microdialysis catheter has been equated to an artificial blood vessel, which is introduced into the tissue. By means of this 'vessel' the concentrations of compounds in the interstitial space can be monitored. The concentration of substances in the collected samples is dependent on the rate of perfusate flow. When perfusate flow is slow enough to allow complete equilibration between interstitial and perfusate fluids, the concentration in the perfusate is maximal and identical to the interstitial concentration. Microdialysis data may be influenced by changes in blood flow, especially in instances where the tissue diffusivity limits the recovery in vivo, i.e. when recovery in vitro is 100 %, whereas the recovery in vivo is less than 100 %. Microdialysis data indicate that a significant arterial-interstitial glucose concentration gradient exists in skeletal muscle but not in adipose tissue at rest. While the concentrations of glucose and lactate in the dialysate from skeletal muscle are close to the expected values, the glycerol values obtained for muscle are still puzzling. Ethanol added to the perfusate will be cleared by the tissue at a rate that is determined by the nutritive blood flow (the microdialysis ethanol technique). It is concluded that microdialysis of skeletal muscle has become an important technique for mechanistic studies in human metabolism and nutrition.

Abstract 372: The Endothelial Glycocalyx Promotes Homogenous Blood Flow Distribution within the Microvasculature

2016 ◽  
Vol 36 (suppl_1) ◽  
Author(s):  
P Mason McClatchey
Keyword(s):  
Fluid Dynamics ◽  
Blood Flow ◽  
Blood Viscosity ◽  
Tissue Perfusion ◽  
Microvascular Perfusion ◽  
Endothelial Glycocalyx ◽  
Heterogeneous Distribution ◽  
Disease States

Introduction: Impaired tissue oxygenation is observed in many disease states including congestive heart failure, diabetes, cancer and aging. Decreased tissue perfusion and heterogeneous distribution of blood flow in the microvasculature contributes to this pathology. The physiological mechanisms regulating homogeneity/heterogeneity of microvascular perfusion are presently unknown. We hypothesized that microfluidic properties of the glycocalyx would promote perfusion homogeneity. Methods: To test our hypothesis, we used established empirical formulations for modelling blood viscosity in vivo (blood vessels) and in vitro (glass tubes). We first assess distribution of blood flow in idealized arteriolar networks. We next simulated distribution of blood flow at an idealized capillary bifurcation. Finally, we simulated velocity profiles and pressure gradients within the vessel lumen with varying glycocalyx properties using a computational fluid dynamics approach. Results: We found that transit time heterogeneity (as assessed by STD to mean ratio) was increased approximately 9x (6.9x-10.6x) using in vitro formulations of blood viscosity relative to in vivo formulations. This effect was mathematically accounted for by increased effective blood viscosity in smaller arterioles. We also found that distribution of blood flow at an idealized microvascular bifurcation was more symmetric using the in vivo formulation than the in vitro formulation (approximately 2x greater disparity between flow in downstream vessels). This effect was mathematically accounted for by an increased hematocrit dependence of blood viscosity. Both the diameter- and hematocrit-based changes in blood viscosity were entirely predictable from fluid dynamics simulations incorporating a space-filling, semi-permeable glycocalyx layer. Summary: Our simulations indicate that the mechanical properties of the endothelial glycocalyx promote homogeneous microvascular perfusion. Conclusions: The literature provides evidence of both glycocalyx degradation and impaired tissue perfusion in the same disease states. Preservation or restoration of normal glycocalyx properties may be a viable strategy for improving tissue perfusion in a wide variety of diseases.

Arteriolar network response to pressure reduction during sympathetic nerve stimulation in cat skeletal muscle

1994 ◽  
Vol 266 (3) ◽  
pp. H1251-H1259 ◽  
Author(s):  
P. Ping ◽  
P. C. Johnson
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Nerve Stimulation ◽  
Sympathetic Nerve ◽  
Similar Degree ◽  
Sartorius Muscle ◽  
Pressure Reduction ◽  
Third Order ◽  
Sympathetic Nerve Stimulation ◽  
Resistance Change

Previous studies in this laboratory have shown that autoregulation of blood flow and dilation of midsized (second-order) arterioles were significantly enhanced during sympathetic nerve stimulation of cat sartorius muscle apparently because of a greater myogenic response of the arterioles. Quite typically, blood flow increased with arterial pressure reduction to 80, 60, and 40 mmHg (superregulation) during sympathetic nerve stimulation. To determine the contribution of the various orders of arterioles to the enhanced autoregulation, we measured diameters in all orders of arterioles and measured red cell velocity in first-, second-, and third-order arterioles. Without sympathetic nerve stimulation, all orders of arterioles except the first order dilated to pressure reduction, but flow autoregulation was weak. With sympathetic nerve stimulation, arteriolar dilation to pressure reduction was significantly enhanced in all six orders of arterioles, and flow rose significantly. The resistance change in the arteriolar network during pressure reduction as calculated from diameter changes was greatest in third- and fourth-order arterioles. Experimentally determined flow changes to pressure reduction and to sympathetic nerve stimulation were quantitatively similar to those predicted from diameter changes in a model of the arteriolar network. Calculated wall shear stress (from viscosity and shear rate) for first-, second-, and third-order arterioles decreased during pressure reduction with and without sympathetic nerve stimulation. We concluded that endothelium-mediated dilation due to shear stress would tend to oppose autoregulation of blood flow to a similar degree under both circumstances.

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