Interstitial Fluid Flux Research Articles

Interstitial flow, pressure and residual stress in the aging carotid artery model in FEBio.

Vascular smooth muscle cells (VSMCs) are subject to interstitial flow-induced shear stress, which is a critical parameter in cardiovascular disease progression. Transmural pressure loading and residual stresses alter the hydraulic conductivity of the arterial layers and modulate the interstitial fluid flux through the arterial wall. In this paper, a biphasic multilayer model of a common carotid artery (CCA) with anisotropic fiber-reinforced soft tissue and strain-dependent permeability is developed in FEBio software. After the verification of the numerical predictions, age-related arterial thickening and stiffening effects on arterial deformation and interstitial flow are computed under physiological geometry and physical parameters. We found that circumferential residual stress shifts outward in each layer and its gradient increases up to 6 times with aging. Internally pressurized CCA displays nonlinear deformation. In the aged artery, the circumferential stress becomes greater on the media layer (82-158kPa) and lower on the intima and adventitia (19-23kPa and 25-28kPa, respectively). The radial compression of the intima reduces the total hydraulic conductivity by 48% in the young and 16% in the aged arterial walls. Consequently, the average radial interstitial flux increases with pressure by 14% in the young and 91% in the aged arteries. Accordingly, the flow shear stress experienced by the VSMCs becomes more significant for aged arteries, which may accelerate cardiovascular disease progression compared to young arteries.

Cranioplasty Reverses Dysfunction of the Solutes Distribution in the Brain Parenchyma After Decompressive Craniectomy.

Solutes distribution by the intracranial cerebrospinal fluid (CSF) fluxes along perivascular spaces and through interstitial fluid (ISF) play a key role in the clearance of brain metabolites, with essential functions in maintaining brain homeostasis. To investigate the impact of decompressive craniectomy (DC) and cranioplasty (CP) on the efficacy of solutes distribution by the intracranial CSF and ISF flux. Mice were allocated in 3 groups: sham surgery, DC, and DC followed by CP. The solutes distribution in the brain parenchyma was assessed using T1 magnetic resonance imaging after injection of DOTA-Gadolinium in the cisterna magna. This evaluation was performed at an early time point following DC (after 2 d) and at a later time point (after 15 d). We evaluated the solutes distribution in the whole brain and in the region underneath the DC area. Our results demonstrate that the global solutes distribution in the brain parenchyma is impaired after DC in mice, both at early and late time-points. However, there was no impact of DC on the solutes distribution just under the craniectomy. We then provide evidence that this impairment was reversed by CP. The solute distribution in the brain parenchyma by the CSF and ISF is impaired by DC, a phenomenon reversed by CP.

Endothelin, Ang II, vasopressin and osmolality regulate hyaluronan turnover by renomedullary interstitial cells suggesting an involvement of this matrix component in fluid handling (860.9)

The content of the matrix component hyaluronan (HA) change in the medullary interstitium in relation to hydration status in vivo: elevated during hydration, reduced during dehydration suggesting a role in fluid handling by affecting interstitial fluid flux. We examined the effect of osmolality and fluid regulating hormones on HA‐turnover by RMIC in culture. Reducing media osmolality to simulate hydration, increased supernatant HA 4‐fold. Cell HA synthase (HAS) 2 and Hyaluronidase (Hyal) 2 mRNA expressions were unaltered while Hyal 1 mRNA was reduced by 35%. Supernatant Hyal activity was reduced by 44%. An inhibitor of Hyal activity (Asc‐P) elevated HA to similar high levels as low osmolality. AngII reduced HA by 58% and combined treatment with vasopressin reduced HA even further (69%). HAS and Hyal mRNA were stable while Hyal activity increased by 38% by AngII and 67% by the combination. Low dose endothelin (ET, 10‐10M) increased HA 3‐fold which was inhibited by ET‐B receptor blocker BQ788. On the contrary, high dose ET (10‐6M) reduced HA by 47%. The ET‐A receptor antagonist BQ123 not only reversed the reducing effect of high dose ET on HA but elevated it to the same level as low dose ET suggesting importance of ET‐B receptors. The study demonstrates a regulatory influence of osmolality and fluid regulating hormones on HA turnover, supporting the concept of an involvement of medullary interstitial HA in renal fluid handling by affecting interstitial permeability.Grant Funding Source: Supported by the Swedish Research Council‐Medicine

A computational study of systemic hydration in vocal fold collision

Mechanical stresses develop within vocal fold (VF) soft tissues due to phonation-associated vibration and collision. These stresses in turn affect the hydration of VF tissue and thus influence voice health. In this paper, high-fidelity numerical computations are described, taking into account fully 3D geometry, realistic tissue and air properties, and high-amplitude vibration and collision. A segregated solver approach is employed, using sophisticated commercial solvers for both the VF tissue and glottal airflow domains. The tissue viscoelastic properties were derived from a biphasic formulation. Two cases were considered, whereby the tissue viscoelastic properties corresponded to two different volume fractions of the fluid phase of the VF tissue. For each case, hydrostatic stresses occurring as a result of vibration and collision were investigated. Assuming the VF tissue to be poroelastic, interstitial fluid movement within VF tissue was estimated from the hydrostatic stress gradient. Computed measures of overall VF dynamics (peak airflow velocity, magnitude of VF deformation, frequency of vibration and contact pressure) were well within the range of experimentally observed values. The VF motion leading to mechanical stresses within the VFs and their effect on the interstitial fluid flux is detailed. It is found that average deformation and vibration of VFs tend to increase the state of hydration of the VF tissue, whereas VF collision works to reduce hydration.

Fluid penetration effects in porous media contact

The contact boundary conditions at the interface between two fluid-saturated porous bodies are derived. The general derivation is performed within the well-founded framework of the Theory of Porous Media (TPM) based on the constituent balance relations of mass, momentum, and energy accounting for finite discontinuities at the contact surface. Particular attention is drawn to the effects associated with the interstitial fluid flux across the interface. The derived contact conditions include two kinematic continuity conditions for the solid velocity and the fluid seepage velocity as well as two jump conditions for the effective solid stress and the pore-fluid pressure. As an application, the common case of biphasic porous media contact proceeding from materially incompressible constituents and inviscid fluid properties is discussed in detail.

Depth-Dependence and Time-Dependence in Mechanical Behaviors of Articular Cartilage in Unconfined Compression Test under Constant Total Deformation

Articular cartilage has high water content from 70 to 80% and biphasic property. The structures of the tissue are inhomogeneous and anisotropy. Consequently, cartilage tissue shows complicated viscoelastic behavior to mechanical stimuli because of depth-dependent and time-dependent interstitial fluid flux and stress-strain behaviors. Therefore it is necessary to consider not only the average tissue property but also the local one to explain mechanical and functional behaviors. The aim of this study is to consider the effect of elastic modulus distribution on the mechanical behavior of cartilage tissue using experiments with visualization and two-dimensional finite element method (FEM).In this study, we performed the compression test of the articular cartilage under the unconfined condition. First, on the basis of the distribution of Young's modulus in depth direction calculated from local strain at equilibrium in experiment, the stress and strain behaviors in articular cartilage were analyzed by biphasic theory.Immediately after loading, the FEM analysis for deformed profiles of the model with depth-dependent Young's modulus corresponded to actual profiles, while the model with average value for Young's modulus showed inadequate deformed profiles. However, the total load-carrying capacity estimated in FEM for the former model is about one order lower than the experimental one measured by a load cell. Therefore, we provided time-dependence to elastic property to understand the complicated viscoelastic behavior during stress relaxation. Thus, the deformed shape profiles of the model immediately after loading and the total load-carrying capacity could satisfactorily correspond to measured data by considering depth-dependent and time-dependent variation of elastic property.

Effect of increased interstitial fluid flux on fractional catabolic rate of high molecular weight [3H]hyaluronan injected in rabbit skin.

The removal rate of high molecular weight (M(r) 3 x 10(6) [3H]hyaluronan has been measured in rabbit paw skin in control and during increased local venous pressure induced by ligation of the femoral vein. The increased venous pressure resulted in a 20% increase of interstitial volume at 4 h after ligation, a value which relates to at least a doubling of lymph flow, i.e. also to doubling of fluid flux through the tissues. The fractional catabolic rate of hyaluronan was 0.0918 +/- 0.0170 h-1 (n = 10) and 0.0775 +/- 0.0206 h-1 (n = 11) in control and following increased venous pressure respectively (P > 0.05). Since the fractional catabolic rate of hyaluronan is not affected by increased venous pressure, the removal of hyaluronan via lymphatic drainage in rabbit paw skin must be small compared to the local turnover of the polysaccharide.

Fluid therapy in burns

Abstract: The dissertation evaluates changes in transcapillary fluid and protein balance in the initial phase after extensive burns, comparing the effects of different regimens for post‐burn fluid resuscitation.Studies were performed in anaesthetized rats and sheep. Within 15 min after major thermal injury, cardiac output (CO) was reduced by 40–50%, mainly due to a reduced stroke volume. Mean arterial pressure (MAP) also dropped by 30–40 mmHg. Both lactated Ringer's and plasma improved this postburn circulatory impairment.Rapid bolus infusions of small volumes of very hypertonic saline, 7.5% NaCl (2 400 mosmol/1), have rapidly corrected the circulatory impairment in haemorrhagic shock. Following a rapid bolus infusion of 7.5% NaCl in 6% Dextran 70, CO and MAP were completely restored, but the effect only lasted 30–60 min. When administered by a slow infusion, 7.5% NaCl gave no circulatory improvement.The transcapillary colloid‐osmotic gradient was maintained in injured skin following infusion of plasma, whereas it was almost annihilated by infusion of lactated Ringer's. Plasma infusion thus induced a protein‐rich edema in injured skin, whereas lactated Ringer's resulted in a generalized edema.Increased interstitial fluid flux can mobilize the interstitial matrix protcoglycan hyaluronan. Following burn injury, plasma concentrations of hyaluronan increased up to ten times above baseline. This observation suggests that at least some of the degradation of structural connective tissue components in thermally injured skin is by lymphatic removal (and subsequent degradation in liver). Increased plasma concentrations of interstitial components have not previously been observed after thermal injury.

Turnover of hyaluronan in the microcirculation.

Hyaluronan in skin, lung, and intestine turns over within a few days and catabolism takes place locally in the tissues, in local lymph nodes, and in the liver. Hyaluronan will affect microcirculatory exchange through its influence on interstitial volume exclusion, hydraulic conductivity, and diffusivity of macromolecules. Prolonged increase in interstitial fluid flux in intestine has been shown to reduce the hyaluronan content, which in turn increases hydraulic conductivity and diffusivity of macromolecules.

Hyaluronan flux from cat intestine: changes with lymph flow.

Isolated and autoperfused ileal segments from pentobarbital-anesthetized cats were used to study turnover of hyaluronan in the intestine. A postnodal lymphatic was cannulated, and transcapillary and interstitial fluid fluxes were increased by raising venous pressure. Lymph hyaluronan concentration in control averaged 20.2 +/- 18.8 (SD) micrograms/ml (range 4.6-50) and increased with increasing lymph flow in all experiments to peak at concentrations two to three times above control values (at 15-20 mmHg increase in venous pressure). At higher lymph flows, hyaluronan concentration fell to below 5 micrograms/ml to an average of 21.3 +/- 19.5% of control value at the highest venous pressures used (30-40 mmHg). Tissue hyaluronan content fell from 349 +/- 191 micrograms/g dry wt in control to 148 +/- 78 micrograms/g dry wt (P less than 0.05) at the end of the experiment. In a second group, vasodilators were administered before elevation of venous pressure to prevent redistribution of blood flow between mucosal and muscular layers. The results were similar to those obtained above. In a third experimental group, venous pressure was elevated in one step to 30 mmHg and maintained at this level. Again, hyaluronan concentration initially increased and later fell well below control values. We conclude that a major part of the intestinal hyaluronan is easily mobilized by increased interstitial fluid flux.

Prostaglandin infusion and endotoxin-induced lung injury.

The use of prostaglandins is currently undergoing clinical trials in respiratory failure accompanying sepsis. The effect of prostaglandin E1 (PGE1) and prostacyclin (PGI2) infusion on endotoxin-induced lung injury, with attention to interstitial fluid flux (QL), pulmonary vascular pressure (Ppa), leukocytes, platelets, and release of the lysosomal enzyme beta-glucuronidase, was investigated. A chronic lung lymph fistula model in sheep was used. Seven sheep alternately received Escherichia coli endotoxin and endotoxin plus PGE at a dosage of 1 microgram/kg/min. Six sheep received PGI2 (0.2 microgram/kg/min) instead of PGE1. Both PGE1 and PGI2 decreased the pulmonary hypertension and the interstitial edema produced by endotoxin primarily through their vasodilatory properties. Prostacyclin seemed to have an additional membrane-stabilizing effect. A rebound increase in QL, Ppa, and platelets occurred when PGE1 or PGI2 infusion was discontinued.