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PubMed1990

Quantitative studies of hydrodynamic effects and cross-relaxation in protein solutions and tissues with proton and deuteron longitudinal relaxation times.

Longitudinal relaxation times T1 of water protons were measured in 5% protein solutions at different static magnetic fields (0.47, 2, and 7 T), for proteins with molecular weight ranging between 1.4 and 480 kDa and in solvents of varying degrees of deuteration. T1 values were also obtained for rat liver soaked with Krebs-Ringer solutions of varying degrees of deuteration at the above fields. For the samples containing D2O, T1 for deuterium was also measured at fields 2 and 7 T. The deuterium measurements were used to estimate water rotational correlation times which were in turn used to estimate the contribution of so-called "hydrodynamic effects" of macromolecules to proton relaxation. The proton relaxation rates at full deuteration were compared with those in protonated solvent (water) to obtain a second, direct measurement of this effect. Both measurements provide quantitation of the hydrodynamic effects, free from the contributions of other effects that are transparent to deuteration, and results from both measurements agree with each other reasonably well. The cross-relaxation rate between solute and solvent protons, and the contribution of paramagnetic impurities in the samples were also obtained from the proton T1 studies. The experimental results show that the hydrodynamic effects (intramolecular and intermolecular water-water interactions) are about the same magnitude in all the proteins studied as well as in rat liver. However, the cross-relaxation rate generally increases with increasing protein molecular weight. Measurements in soaked rat liver indicate that the cross-relaxation rate per unit mass of solute is much higher in tissues than in simple solutions of proteins of similar mean molecular weight. The results challenge the prevailing concept that the relaxation properties of biological tissues may be treated as a simple superposition of the properties of their constituents.

Animals↗
PubMed1996

Hydrodynamics of Fractal Aggregates with Radially Varying Permeability.

Hydrodynamic properties of fractal aggregates with radially varying permeability are investigated in terms of two parameters: radius of equivalent solid sphere experiencing the same drag as the aggregate (Omega*radius of aggregate) and fluid collection efficiency (eta) of the aggregate. Resistance to the fluid flow through the aggregate is predicted to increase with increasing fractal dimension, while the fluid collection efficiency is expected to decrease. It is shown that a reasonable estimate of the fluid drag force on a fractal aggregate may be obtained by assigning a constant volume-averaged porosity to the aggregate and using any of the expressions available in the literature for aggregates with uniform permeability. The two hydrodynamic parameters, Omega and eta, are used to modify the existing expressions for interactions between solid spheres to account for the porous nature of aggregates and thus calculate the collision rate kernels for interacting aggregates. The ratio of hydrodynamic radius of an aggregate to its radius of gyration predicted by the proposed model was in reasonable agreement with an experimental value reported in the literature.

Journal Article↗
PubMed2002

Hydrodynamic interaction between spheres coated with deformable thin liquid films.

In this article, we considered the hydrodynamic interaction between two unequal spheres coated with thin deformable liquids in the asymptotic lubrication regime. This problem is a prototype model for drop coalescence through the so-called "film drainage" mechanism, in which the hydrodynamic contribution comes dominantly from the lubrication region apart from the van der Waals interaction force. First, a general formulation was derived for two unequal coated spheres that experienced a head-to-head collision at a very close proximity. The resulting set of the evolution equations for the deforming film shapes and stress distributions was solved numerically. The film shapes and hydrodynamic interaction forces were determined as functions of the separation distance, film thickness, viscosity ratios, and capillary numbers. The results show that as the two spheres approach each other, the films begin to flatten and eventually to form negative curvature (or a broad dimple) at their forehead areas in which high lubrication pressure is formed. The dimple formation occurs earlier as the capillary number increases. For large capillary numbers, the film liquids are drained out from their forehead areas and the coated liquid films rupture before the two films "touch" each other. Meanwhile, for small capillary numbers, the gap liquid is drained out first and the two liquid films eventually coalesce.

Journal Article↗
PubMed1991

The time course and frequency content of hydrodynamic events caused by moving fish, frogs, and crustaceans.

In the present study the time course and spectral-amplitude distribution of hydrodynamic flow fields caused by moving fish, frogs, and crustaceans were investigated with the aid of laser-Doppler-anemometry. In the vicinity of a hovering fish sinusoidal water movements can be recorded whose velocity spectra peak below 10 Hz. Single strokes during startle responses or during steady swimming of fish, frogs, and crustaceans cause short-lasting, low-frequency (less than 10 Hz), transient water movements. Low-frequency transients also occur if a frog approaches and passes a velocity-sensitive hydrodynamic sensor. In contrast, transient water movements caused by a rapidly struggling or startled fish or water motions measured in the wake of a slowly swimming (less than or equal to 47 cm/s) trout can be broadbanded, i.e., these water movements can contain frequency components up to at least 100 Hz. High-frequency hydrodynamic events can also be measured behind obstacles submerged in running water. The possible biological advantage of the ability to detect high-frequency hydroynamic events is discussed with respect to the natural occurrence of high frequencies and its potential role in orientation and predator-prey interactions of aquatic animals.

Animals↗
PubMed1976

The effect of renal hydrodynamics on immune complex deposition.

The role of renal hydrodynamics on renal deposition of immune complexes was evaluated in acute serum sickness. Using i.v. radiolabelled antigen in rabbits under a variety of hydrodynamic alterations, these studies suggested that although intrarenal hydrodynamics influence renal deposition of immune complexes factors other than intrarenal hydrostatic pressure may be important.

Animals↗
PubMedDate not supplied

Percutaneous hydrodynamic thrombectomy for congenital deep vein thrombosis in a neonate.

A 1-day-old boy with a complete occlusive inferior vena cava and bilateral renal vein thrombus removed successfully using a hydrodynamic thrombectomy catheter is reported. Although blood flow to the inferior vena cava and bilateral renal veins was restored with no distal embolism or vascular injury, he died of bleeding complications due to fibrinolytic therapy after hydrodynamic thrombectomy. To the best of our knowledge, this is the first report of hydrodynamic thrombectomy of a neonate.

Angioplasty, Balloon↗
PubMed2003

Modeling the hydration of proteins: prediction of structural and hydrodynamic parameters from X-ray diffraction and scattering data.

The implications of protein-water interactions are of importance for understanding the solution behavior of proteins and for analyzing the fine structure of proteins in aqueous solution. Starting from the atomic coordinates, by bead modeling the scattering and hydrodynamic properties of proteins can be predicted reliably (Debye modeling, program HYDRO). By advanced modeling techniques the hydration can be taken into account appropriately: by some kind of rescaling procedures, by modeling a water shell, by iterative comparisons to experimental scattering curves (ab initio modeling) or by special hydration algorithms. In the latter case, the surface topography of proteins is visualized in terms of dot surface points, and the normal vectors to these points are used to construct starting points for placing water molecules in definite positions on the protein envelope. Bead modeling may then be used for shaping the individual atomic or amino acid residues and also for individual water molecules. Among the tuning parameters, the choice of the scaling factor for amino acid hydration and of the molecular volume of bound water turned out to be crucial. The number and position of bound water molecules created by our hydration modeling program HYDCRYST were compared with those derived from X-ray crystallography, and the capability to predict hydration, structural and hydrodynamic parameters (hydrated volume, radius of gyration, translational diffusion and sedimentation coefficients) was compared with the findings generated by the water-shell approach CRYSOL. If the atomic coordinates are unknown, ab initio modeling approaches based on experimental scattering curves can provide model structures for hydrodynamic predictions.

Binding Sites↗
PubMed1999

Calculation of hydrodynamic properties of macromolecular bead models with overlapping spheres.

For the calculation of hydrodynamic properties of rigid macromolecules using bead modelling, models with overlapping beads of different sizes are used in some applications. The hydrodynamic interaction tensor between unequal overlapping beads is unknown, and an oversimplified treatment with the Oseen tensor may introduce important errors. Here we discuss some aspects of the overlapping problem, and explore an ad hoc form of the interaction tensor, proposed by Zipper and Durchschlag. We carry out a systematic numerical study of the hydrodynamic properties of a two-spheres model, showing how the Zipper-Durchschlag correction removes efficiently the numerical instabilities, and predicts the correct limits.

Biophysical Phenomena↗
PubMed2005

Hydrodynamic detection by cupulae in a lateral line canal: functional relations between physics and physiology.

In the present review, signal-processing capabilities of the canal lateral line organ imposed by its peripheral architecture are quantified in terms of a limited set of measurable physical parameters. It is demonstrated that cupulae in the lateral line canal organ can only partly be described as canal fluid velocity detectors. Deviation from velocity detection may result from resonance, and can be characterized by the extent to which a single dimensionless resonance number, N ( r ), exceeds 1. This number depends on four physical parameters: it is proportional to cupular size, cupular sliding stiffness and canal fluid density, and inversely proportional to the square of fluid viscosity. Situated in a canal, a cupula may benefit from its resonance by compensating for the limited frequency range of water motion that is efficiently transferred into the lateral line canal. The peripheral transfer of hydrodynamic signals, via canal and cupula, leads to a nearly constant sensitivity to outside water acceleration in a bandwidth that ranges from d.c. to a cut-off frequency of up to several hundreds of Hertz, significantly exceeding the cut-off frequency of the lateral line canal. Threshold values of hydrodynamic detection by the canal lateral line organ are derived in terms of water displacement, water velocity, water acceleration and water pressure gradients and are shown to be close to the detection limits imposed by hair cell mechano-transduction in combination with the physical constraints of peripheral lateral line signal transfer. The notion that the combination of canal- and cupular hydrodynamics effectively provides the lateral line canal organ with a constant sensitivity to water acceleration at low frequencies so that it consequently functions as a low-pass detector of pressure gradients, supports the appropriateness of describing it as a sense organ that "feels at a distance" (Dijkgraaf in Biol Rev 38:51-105, 1963).

Animals↗
PubMed2007

Hydrodynamic focusing investigation in a micro-flow cytometer.

Hydrodynamic focusing behavior is characterized by two fluids coflowing at different velocities inside a micro-flow cytometer. In this study, a two-fluid model has been established to describe the flow transport behavior and interaction of sample and sheath fluids. The analysis treats the sample and sheath fluids as two-dimensional, laminar, incompressible, and isothermal. The theoretical model comprises two groups of transient conservation equations of mass and momentum with consideration of the interfacial momentum exchange. The governing equations are solved numerically through an iterative SIMPLEC algorithm to determine the flow properties. Since the ratio of the sheath velocity to the sample velocity varies from 5 to 70, the predicted focusing width and length are in good agreement with the experimental data in the literature. In addition, the present study explored the hydrodynamic focusing flowfield as well as the pressure drop across a micro-flow cytometer and the time needed for the completion of one focusing event in detail. To enhance the understanding of hydrodynamic focusing in the design of cytometers, ten numerical experiments were conducted to examine the effects of the inner nozzle length, inner nozzle exit width, inner nozzle shape, and fluid properties on the width of the focused sample stream.

Computer Simulation↗
PubMed1991

Comparative study of the hydrodynamic function of the CarboMedics valve.

The hydrodynamic function of each size of the CarboMedics valve was assessed in a pulsatile flow simulator. The mean pressure difference with respect to forward flow, regurgitant volumes, and total energy loss across each valve were analyzed. The results for the 23-mm aortic and 29-mm mitral CarboMedics valves were compared with those for the St. Jude Medical and Björk-Shiley Monostrut valves. Results showed good hydrodynamic function for each CarboMedics valve, although the pressure difference and total energy loss across the 19-mm aortic valve was high. The hydrodynamic function of the CarboMedics valve was comparable with that of the St. Jude Medical valve. Both valves showed similar leakage volumes, which were significantly larger than that for the Björk-Shiley Monostrut valve. On account of this the total energy loss in the Björk-Shiley valve was significantly less than that for the bileaflet valves in the aortic position. Concern remains for the continuing presence of high closed-valve regurgitation in the bileaflet valves.

Aortic Valve↗
PubMed1979

A computer model for hydrodynamic shearing of DNA (Gibb's phenomenon): Part II.

This paper presents an extension of the distribution proposed during hydrodynamic shearing of DNA. In the Fourier least square approximation of uniform random distribution or a square wave, Gibb's phenomena occur at the boundaries. The same behavior occurs at the boundaries of the DNA strands undergoing hydrodynamic shearing of DNA. This hypothesis is corroborated by results from a computer simulation of hydrodynamic shearing of DNA. The evidence helps confirm the kinetic experiments of Britten and Kohne [4]. Furthermore the results predict that sequence very near the end (0.2 LAMBDA) should be the most intact.

Computers↗
PubMed1986

Rabbit chondrocytes maintained in serum-free medium. I. Synthesis and secretion of hydrodynamically-small proteoglycans.

The biosynthesis of sulfated proteoglycan in vitro by rabbit articular chondrocytes in first passage monolayer culture maintained in fetal bovine serum (FBS) or in serum-free conditions was compared. Neosynthesized proteoglycan in the culture medium in the most dense fraction of an associative CsCl density gradient (fraction dAl) declined with increasing time under serum-free conditions, but not when cells were maintained in the presence of serum. After one day, the major peak of incorporated 35SO4 in medium fraction dAl eluted as a retarded peak (Kav 0.28) on Sepharose CL-2B, whether cells were maintained under serum-free or serum-containing conditions. The hydrodynamic size of proteoglycan monomer fraction dAlDl obtained after one day of exposure to serum-free culture media was smaller than dAlDl from serum-containing cultures. The hydrodynamic size of dAlDl obtained from serum-free culture media became even progressively smaller after 2 and 3 days' exposure to these conditions. Hydrodynamically small sulfated proteoglycans were identified in the cell-associated dAlDl fraction as early as one day after switching chondrocytes from serum-containing to serum-free medium. Culture medium fraction dAlDl from serum-free culture medium aggregated poorly when incubated with human hyaluronic acid (HA) in the presence of bovine link protein or when dialysed against bovine nasal cartilage proteoglycan aggregate. Proteoglycan monomer from serum-containing medium reaggregated more efficiently under both conditions. No change in the size of glycosaminoglycan chains was seen in the smaller proteoglycan subpopulations, nor was there any indication of marked changes in the glycosaminoglycan types.

Animals↗
PubMed1990

Hydrodynamic data show that C1- inhibitor of complement forms compact complexes with C1-r and C1-s.

The C1- inhibitor of the complement cascade forms stoichiometric complexes with C1-r and C1-s and controls the activation of first component C1 of complement. Literature sedimentation coefficients s degrees 20,w for the complexes formed between C1- inhibitor, C1-r and C1-s were analysed using frictional ratios and the hydrodynamic sphere approach. A head-and-tail two-domain model for C1- inhibitor was combined with cylindrical hydrodynamic models for the six-domain structures of C1-r and C1-s. The hydrodynamic data show that the heavily glycosylated N-terminal domain of C1- inhibitor is positioned close to the two complement 'short consensus repeat' domains found in the centre of C1-r and C1-s.

Complement Activation↗
PubMed1990

Mass fractionation of noble gases in diffusion-limited hydrodynamic hydrogen escape.

Mass fractionation by hydrodynamic hydrogen escape is a promising mechanism for explaining the observed elemental and isotopic abundance patterns in terrestrial planet atmospheres. Previous work has considered only pure hydrogen winds. Here, the theory of mass fractionation by hydrogen escape is extended to atmospheres in which hydrogen is not the only major constituent. Analytical solutions are derived for cases in which all relevant atmospheric constituents escape; both analytical and numerical solutions are obtained for cases in which important heavy constituents are retained. In either case the fractionation patterns that result can differ significantly from those produced by pure hydrogen winds. Three applications of the theory are discussed: (1) The observed fractionation of terrestrial atmospheric neon with respect to mantle neon can be explained as a by-product of diffusion-limited hydrogen escape from a steam atmosphere toward the end of accretion. (2) The anomalously high Martian (SNC) 38Ar/36Ar ratio is attributed to hydrodynamic fractionation by a vigorously escaping, nearly pure hydrogen wind. (3) It is possible that the present high Martian D/H ratio was established during the same hydrodynamic escape phase that fractionated argon, but the predicted degree of D/H enrichment is sensitive to other, less well constrained parameters.

Argon↗
PubMed1994

Hydrodynamic simulation of arterial networks which include compliant and rigid bypass grafts.

The conditions required to produce an ideal bypass graft have not yet been determined. In order to understand the hemodynamic impact of bypass grafts on cardiovascular function, a hydrodynamic model for the part of the human arterial network below the renal arteries has been constructed. The results from this physical model were used to validate a digital computer model of the arterial network developed by the authors, that incorporated loops which occur due to bypass grafts. The hydrodynamic model was designed to study the interaction between an arterial stenosis and bypass graft and, in particular, the effect of the compliance of the graft on their function. In the model, similarity laws have been maintained with regard to geometry, viscosity, peripheral resistance, wall elastic properties, pulse shape, and blood flow rate. Measured and predicted pressure and flow wave-forms showed an increase in their mean and peak values for the healthy leg when the bypass graft was closed. There was also a severe pressure drop across the stenosis and a marked decrease in mean and pulsatile flow in the stenotic leg. The stenosis in the hydrodynamic model produced similar behaviour to published results obtained on animals. When the graft was open, the agreement between our experimental and theoretical model was within 5% and both the pressure and flow waves were almost similar at the maxima and minima in both legs. Although the arterial system is non-linear, the non-linearities are shown to be of insignificant magnitude and therefore, we have concluded that the pressure flow relationship is essentially linear. The effect of the degree of compliance of the graft and the 'steal' phenomenon due to the graft have been investigated. It was found that there were no significant differences in the flow delivery between the compliant graft and stiff graft. Also, there was no 'steal'. Thus the compliance of the graft is not a significant factor in promoting its patency.

Arteries↗
PubMed1990

Hydrodynamic deposition: a novel method of cell immobilization.

A novel method of cell immobilization is described. The cell support consists of ceramic microspheres of approximately 50-75 microns diameter. The spheres are hollow, having a wall thickness of 10-15 microns and one entrance (ca. 20 microns diameter). The walls are porous with a mean pore size of approximately 90 nm. When a cell suspension (of S. cerevisiae) is passed through a column of such particles, cells are immobilized. Conditions are devised such that the overwhelming majority of cells are held in the central cavity of the support and not between the particles. Provided turbulence is avoided, the distribution of cells along the column length in the steady state is rather homogeneous. The facts that (a) essentially all particles, regardless of orientation, entrap cells, and (b) nonporous particles also entrap cells with high efficiency, indicate that filtration effects are irrelevant and that heretofore unrecognized hydrodynamic forces are alone responsible for the cell immobilization. Cells can be immobilized to high biomass densities, while the hydrodynamic properties of columns containing such immobilized cells are excellent. We describe an on-line electronic method for the real-time measurement of immobilized cellular biomass. Cell growth (so recorded) and metabolism continue to occur in such particles at high rates. Using the glycolytic production of ethanol by S. cerevisiae as a model reaction, volumetric productivities as great as any published are obtained. Thus the "lobster-pot effect" or "hydrodynamic deposition" represents a novel, promising, and generally applicable method of cell immobilization.

Biotechnology↗
PubMed1994

Hydrodynamic characteristics and equilibrium rigidity of pullulan molecules.

The hydrodynamic characteristics of the polysaccharide pullulan (polymaltotriose) in water have been investigated and its molecular characteristics have been determined. Experimental values varied over the following ranges: velocity sedimentation coefficient (S): 0.9 < S < 11.2, translational diffusion coefficient (10(7) cm2 s-1): 1.1 < D < 14.7 and intrinsic velocity (cm3 g-1): 6.7 < [eta] < 164, which corresponds to a change in molecular weight (x 10(3)) in the range 3.9 < MSD < 644. On the basis of analysis of the literature and our experimental data, excluded volume effects have been shown to have a prevailing influence on the chain length of these polysaccharides. The equilibrium rigidity and hydrodynamic chain diameter of pullulan were evaluated on the basis of the theory of hydrodynamic properties of a wormlike necklace, taking into account excluded volume effects. At low M (< 30 x 10(3)) the translation friction data (in contrast to viscometric data) cannot be described in the framework of the theory of linear molecules.

Chemical Phenomena↗