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PubMed2002

Hydrodynamic control of nitrogen and phosphorus turnover in an eutrophicated estuary in the Baltic.

The turnover of phosphorus and nitrogen have been studied in a low salinity estuary in the Bothnian Sea. The estuary, Gårdsfjärden, has a high loading of nutrients from a pulp and paper mill which supplies the estuary with three times the annual natural input of phosphorus and nitrogen, respectively. The turnover of nutrients was to a great extent determined by hydrodynamic variations. During periods of intense resuspension there was a net export of particulate bound nutrients from the estuary to the sea but since these periods were short there was an overall net retention of particulate nutrients. The estuary was a source for dissolved phosphorus to the sea. The major source of phosphorus export was release of dissolved P from anoxic sediments. Gårdsfjärden was a sink for dissolved nitrogen which most likely escaped the estuary by denitrification. Nitrate was supplied by degradation of particulate organic nitroge'n but the main source was import from the sea.

Baltic States↗

PubMed2005

Delivery of siRNA and siRNA expression constructs to adult mammals by hydrodynamic intravascular injection.

Extensive use of RNA interference in mammals has been hindered by the inability to effectively deliver small interfering RNAs (siRNAs) or DNA-based constructs designed to express siRNAs. In this chapter, we describe the high-pressure or hydrodynamic intravascular injection technique used to deliver these nucleic acids to mice and nonhuman primates. Emphasis is placed on the use of this technique for delivery to the liver.

Animals↗

PubMed2001

Hydrodynamics of cryogelation.

Cryogel, prevalent in the plasma of rheumatoid arthritis patients, is a plasma fibronectin (pFN)-extra domain A containing FN [EDA(+)FN]-fibrinogen (Fbg) aggregate formed by the addition of heparin (Hep) at low temperature. Although EDA(+)FN is not usually present in normal plasma, its prevalence in rheumatic patients induces cryogelation. In this study, we determined the hydrodynamic radius (R(h)) ratio (R(h)/R(h30)) of the cryogel component by dynamic light scattering in vitro. R(h)/R(h30) was normalized to R(h) at 30 degrees C (R(h30)) at several temperatures. The R(h)/R(h30) of Fbg was found to increase only by self-aggregation, whereas the R(h)/R(h30) of FNs does not increase in response to temperature changes. The R(h)/R(h30) of the Fbg/FN aggregate is increased by the addition of Hep, and the R(h)/R(h30) (12.5) of the Hep-induced EDA(+)FN/Fbg aggregate is greater than that (2.5) of the pFN/Fbg aggregate. These results suggest that cryogelation requires Fbg self-aggregation and the interaction between EDA(+)FN and Hep.

Arthritis, Rheumatoid↗

PubMed1998

Hydrodynamic properties of gelatin in dilute solutions.

Aggregation properties of Gelatin chains in neutral aqueous solutions, are reported in the temperature range T = 35-60 degrees C, from the measured intrinsic viscosity [eta], diffusion coefficient, D(o), molecular weight Mw, and radius of gyration (Rg) data. Gelatin chains doubled their size as the solution was cooled to 35 degrees C from 60 degrees C. The intermolecular interaction was found to be repulsive which showed significant decrease as the temperature was reduced. The data provides excellent fitting to the scaling relations Mw[eta] = (1.96 +/- 0.06) x 10(-26)(Re,eta/Re,D)3(D(o) eta o/T)-3 and (D(o)n1/2)-1 approximately equal to (6 1/2 pie eta o chi beta/kB/T)[1 + 0.201(v/beta 3)n1/2] where n is the number of segments in the chain. The ratio of the hydrodynamic radius (Re,D) (deduced from D(o)) and Rg, (Re,D/Rg = zeta) was found to be 0.555. From the known solvent viscosity eta o, the segment length beta, was deduced to be (15 +/- 2) A. The deduced excluded volume was v approximately equal to (4.1 A)3. The Flory-Huggins interaction parameter (zeta) did not show observable temperature dependence.

Biopolymers↗

PubMed2002

High-molecular-weight protein hydrodynamics studied with a long-lifetime metal-ligand complex.

[Ru(2,2'-bipyridine)(2)(4,4'-dicarboxy-2,2'-bipyridine)](2+) (RuBDc) is a very photostable probe that possesses favorable photophysical properties including long lifetime, high quantum yield, large Stokes' shift, and highly polarized emission. In the present study, we demonstrated the usefulness of this probe for monitoring the rotational diffusion of high-molecular-weight (MW) proteins. Using frequency-domain fluorometry with a high-intensity, blue light-emitting diode (LED) as the modulated light source, we compared the intensity and anisotropy decays of RuBDc conjugated to immunoglobulin G (IgG) and immunoglobulin M (IgM), which show a six-fold difference in MW We obtained slightly longer lifetimes for IgM ( =428 ns in buffer) than IgG ( =422 ns in buffer) in the absence and presence of glycerol, suggesting somewhat more efficient shielding of RuBDc from water in IgM than in IgG. The anisotropy decay data showed longer rotational correlation times for IgM (1623 and 65.7 ns in buffer) as compared to IgG (264 and 42.5 ns in buffer). Importantly, the ratio of the long rotational correlation times of IgM to IgG in buffer was 6.2, which is very close to that of MW of IgM to IgG (6.0). The shorter correlation times are most likely to be associated with domain motions within the proteins. The anisotropy decays reflect both the molecular size and shape of the immunoglobulins, as well as the viscosity. These results show that RuBDc can have numerous applications in studies of high-MW protein hydrodynamics and in fluorescence polarization immunoassays (FPI) of high-MW analytes.

2,2'-Dipyridyl↗

PubMed2000

Analysis of skin permeation-enhancing mechanism of iontophoresis using hydrodynamic pore theory.

The effects of constant DC iontophoresis (0-1.5 mA/0.966 cm(2)) on the permeation of three hydrophilic compounds, antipyrine (ANP, M.W. 188.23), sucrose (SR, M.W. 342.30) and 1-kestose (KT, M.W. 506.73), through excised hairless rat skin were evaluated using hydrodynamic pore theory. The electro-osmotic flow caused by iontophoresis was measured using deuterium oxide (D(2)O). The penetration-enhancing mechanism of iontophoresis was found to increase solvent flow through electro-osmosis and pore enlargement and/or new pore production in the skin barrier, together with enhancement of electrochemical potential difference across the skin. These effects were closely related to the strength of the current applied. The electro-osmotic flow of D(2)O (J(D(2)O)) greatly enhanced the skin permeation clearance of all hydrophilic penetrants (CL(drug)). Pore production was classified into reversible and irreversible processes, which resulted from lower (0-0.5 mA/0.966 cm(2)) and higher (0.5-1. 5 mA/0.966 cm(2)) currents, respectively. Thus, the enhancing effects of iontophoresis on skin permeation of nonionic hydrophilic compounds can be explained by increase in pore size and higher solvent flow.

Administration, Topical↗

PubMed2000

Predicting dissolution via hydrodynamics: salicylic acid tablets in flow through cell dissolution.

A model was established for the dissolution of non-disintegrating salicylic acid tablets as a function of hydrodynamic conditions in the Flow Through Cell system (USP Apparatus 4). The approach was to model the dissolution rate of the material as a function of the Reynold's number, the dimensionless engineering term that describes the degree of turbulence. The dissolution rate of USP calibrator salicylic acid tablets was measured as a function of tablet size, orientation within the cell, dissolution media flow rate, and cell size. All of these variables were found to have an effect on dissolution rate, consistent with theory. An equation to predict this dissolution was established as: N(SH)=-21.1+12.6xN(RE)(0.5), R(2)=0.99; 10<N(re)<292.

Models, Theoretical↗

PubMed2002

Characterisation of nanoparticulate systems by hydrodynamic chromatography.

Particle size and particle size distribution can have a fundamental effect on the physical properties of colloidal dispersions. For many systems the measurement of average particle size is not sufficient, the presence of different size populations will have a strong influence on properties and could be related to the production process. Hydrodynamic chromatography (HDC) provides a method for the separation of polymers in solution or particles in suspension based on their size. In a packed column, the separation takes place in the inter-particle channels and the elution order is from large to small, analogous to gel permeation chromatography. The dynamic range of packed column HDC is from molecular size up to particles of greater than 1 microm. New instrumentation which can be used to determine the particle size distribution of a range of colloidal dispersions by packed column HDC is described. Data to support accuracy and precision of average particle size determination is presented as well as a number of case studies to illustrate the applicability of the technique to samples with polydisperse or multi-modal particle size distributions.

Chromatography↗

PubMed1992

Hydrodynamic analysis of intraocular pressure changes during anterior chamber procedures.

Variations in intraocular pressure (IOP), observed by us and other authors in closed-system anterior chamber procedures, are explained using a simple hydrodynamic analysis based on the Bernoulli equation. Calculations show that the sudden increases in IOP (pressure spikes) measured during anterior segment surgery are due primarily to the small size of the infusion cannulas and are exacerbated by high infusion rates. Accurate measurement of these IOP variations requires placement of the pressure sensors in situ and is not possible by remote pressure sensing at the infusion line or the console. This work indicates that closed-system procedures could benefit from accurate monitoring of intraoperative IOP and could use these measurements for automatic IOP control during surgery.

Animals↗

PubMed2002

Development of a technique for using 99mTc as an adsorbable tracer for hydrodynamic studies of fine sediments in suspension.

Labelling of fine sediment (phi < 62.5 microm) with 99mTc was achieved through laboratory experiments described in a previous work (Proceedings of an International Symposium on Isotope Techniques in Water Resources Development and Management. IAEA-SM-361/13, Vienna, Proceedings of the XIIIth Brazilian Symposium on Water Resources. Brazilian Association for Water Resources (ABRH), Belo Horizonte, paper 176, CD-rom (in Portuguese)). Comparative studies of the hydrodynamic behaviour of the labelled and unlabelled sediment, in order to validate the application of the labelled sediment in field studies, were further performed by means of sedimentation tests using the Andreasen pipette technique, and are presented here. Labelling without flocculation, which promotes the same sedimentation behaviour of the labelled and the natural sediment was only achieved using small quantities of SnCl2 dissolved in proportionately small volumes of HCI (0.3%), in the reduction of a 99mTcO4- eluted from a 99Mo generator.

Journal Article↗

PubMed1995

Comparative study of the hydrodynamic function of six size 19 mm bileaflet heart valves.

The hydrodynamic function of six size 19 mm bileaflet mechanical heart valves was investigated in a pulsatile flow simulator. The St. Jude Standard, St. Jude Haemodynamic Plus, CarboMedics, Sorin Biomedica, Duromedics and ATS valves were studied. The mean pressure drop and effective orifice area during forward flow, regurgitant volumes and total energy loss were analysed. The St Jude Haemodynamic Plus and Sorin Biomedica valves had significantly lower forward flow pressure drops and total energy losses than the other four valves. Assuming that all six valves can be implanted in the equivalent size of aortic root, this should lead to improved in vivo performance.

Aortic Valve↗

PubMedDate not supplied

Distal embolization during thrombectomy with use of the hydrolyser (hydrodynamic thrombectomy catheter): in vitro testing.

PURPOSE: To evaluate distal embolization while using the Hydrolyser (hydrodynamic thrombectomy catheter) with special attention to the severity of the stenosis and temporary distal or proximal flow obstruction. MATERIALS AND METHODS: The Hydrolyser procedure was assessed in plastic tubes (5-8 mm) with a 70% or 90% diameter stenosis with or without temporary distal flow obstruction and a 72-hour-old clot proximal to the stenosis. The weight of the embolized particles was established after passage through filters of 1,000, 500, 100, and 10 microm. To evaluate the influence of the absolute inner diameter of the stenosis 1.0-, 2.1-, and 3.0-mm stenoses were compared in 10-mm tubes. RESULTS: Thrombus removal was greater than 99.9% in all but one of the cases in the 5-8-mm tubes. Embolization with a weight of more than 1 mg was only found in tubes with a relative stenosis of 70% and a stenosis inner diameter of greater than 1.5 mm. There was a positive relationship between inner diameter of the stenosis and the amount of distal embolization. In the presence of a proximal or distal temporary flow obstruction during thrombectomy, no distal embolization greater than 1 mg was found. CONCLUSION: In this in vitro study, the Hydrolyser thrombectomy device demonstrated minimal distal embolization. The amount of distal embolization that did occur was related to the absolute stenosis diameter and could be prevented by a severe distal stenosis and/or a temporary proximal or distal flow obstruction.

Catheterization↗

PubMed1998

Experimental study of the hydrodynamic behaviour of a high frequency ultrasonic reactor.

In relation to design and modeling of sonochemical reactors, the hydrodynamic behaviour of a high-frequency ultrasonic reactor has been investigated. Residence time distribution (RTD) measurements have been performed by means of a tracer method. The influence of ultrasound on the response to an inlet pulse was evidenced. It was shown that the reactor behaves like a completely stirred tank reactor (CSTR) as soon as ultrasonic irradiation operates. Preliminary observations on acoustic streaming occurring within the reactor will also be presented.

Journal Article↗

PubMed2001

Hydrodynamic potential-modulated reflectance spectroscopy: theory and experiment.

This article describes the development and application of a new electrochemical methodology based on potential-modulated UV-vis reflectance spectroscopy (PMRS). The device configuration is based upon a thin-layer flow-through channel cell incorporating a platinum working electrode. Reagent solutions are pumped through the cell under well-defined hydrodynamic conditions and electrolyzed at the platinum working electrode. Measurements are presented for linear sweep and fixed dc potentials with a superimposed small amplitude sinusoidal potential perturbation. A UV-vis source is employed to irradiate the electrode region, and the resulting reflected signal is analyzed using a phase sensitive detector. Experimental studies using tris(4-bromophenyl) amine (TBPA) in acetonitrile are presented which quantify the relationship between the absorption spectrum and reflected light intensity as a function of the transport rate, electrolysis reactions, and the modulation frequency of the incident irradiation. The experimental results are analyzed using numerical simulations based on a finite difference strategy. These permit the quantitative prediction of the concentration distribution of reagents within the cell. A fast Fourier transform (FFT) routine was used to analyze the frequency response of the numerically predicted reflectance signal. Excellent agreement was observed between the numerical predictions and experimental observations.

Journal Article↗

PubMed1989

Hydrodynamic relaxation using stopless flow injection in split inlet sedimentation field-flow fractionation.

In this paper relaxation effects in both the normal and steric operating modes of sedimentation field-flow fractionation are examined by using three different injection procedures: stop flow, stopless flow, and a new stopless flow procedure employing an inlet splitter. In the usual operation of field-flow fractionation (FFF), a stop procedure is used in which the channel flow is halted for an adequate period of time after injection for sample relaxation (in which the sample particles approach equillibrium near one wall) before the resumption of channel flow. If the channel flow is not stopped (stopless flow procedure), the elution profile is shifted and distorted due to the downstream migration of the particles during the relaxation process. To avoid peak distortion while retaining the advantages of the stopless flow procedure, a physical splitter at the channel inlet divides the entering flow stream into two substreams; sample is injected into only one of these. In this way a rapid (although not complete) hydrodynamic relaxation is realized. This stopless split flow injection procedure is compared to ordinary stop and stopless flow procedures using both submicrometer (normal FFF) and supramicrometer (steric FFF) polystyrene latex particles. It is found that much of the distortion normally accompanying stopless flow injection is eliminated by this new procedure. However, further optimization is needed to match the high resolution of the stop flow method.

Chemical Fractionation↗

PubMed2001

A mathematical model for hydrodynamic and size exclusion chromatography of polymers on porous particles.

When packed columns filled with porous particles are used for the separation of macromolecules, either size exclusion chromatography (SEC), hydrodynamic chromatography (HDC), or a combination of both determine the macromolecule retention mechanism. This paper develops a simple mathematical model to describe a molecular weight calibration graph, which includes both HDC and SEC. There is a transition between the HDC calibration region at higher molecular weights to an SEC region at lower molecular weights. The degree to which SEC and HDC are mixed depends on the particle diameter, the relative size of the pores, and the macromolecule size. In addition, using fractal considerations, the fractal character of the apparent selectivity between two adjacent peaks on the chromatogram is shown. This model constitutes an attractive tool to enhance the expansion of these two chromatographic techniques for the separation of biological or synthetical macromolecules.

Journal Article↗

PubMed2002

A chip-based electrophoresis system with electrochemical detection and hydrodynamic injection.

A simple capillary electrophoresis system in the planar format that uses a new, hydrodynamic injection principle is described. The system was realized with poly(dimethylsiloxane)-glass chips and microdisk electrodes for amperometric detection. Using a double-tee injector, no precise voltage control of the electrolyte reservoirs was needed, thus making the microchip CE system more user-friendly. The analytical characteristics of chip-based CE-EC were evaluated using ascorbic acid as the model analyte. The reproducibility of migration time and signal height was expressed by relative standard deviations of 1.2% and 5.1%, respectively (n = 5). The limit of detection for ascorbic acid was approximately 5 microM at a signal-to-noise ratio of 3. Practical application concerning the determination of physiologically relevant compounds such as noradrenaline and L-dopa are discussed.

Ascorbic Acid↗

PubMed2003

Hydrodynamic study of ion transfer at the liquid/liquid interface: the channel flow cell.

A hydrodynamic system based on the channel flow cell for voltammetric detection of ions at the liquid/liquid interface is reported. The current response for tetraethylammonium ion transfer across a membrane-supported liquid/liquid interface is shown to be consistent with existing theory for both the flow rate and voltage scan rate dependence of such processes, with no calibration factors or other adjustable parameters required. The analytical utility of such a device is discussed with specific regard to in situ measurements in flow systems.

Dialysis↗