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At least 415 records · Page 23Linked to original sources
PubMed2000

The in vitro hydrodynamic characteristics of the porcine pulmonary valve and root with regard to the ross procedure.

OBJECTIVE: The hydrodynamic parameters and leaflet motion of the porcine pulmonary root and valve and the performance of the pulmonary autograft implanted in subcoronary position or as a free-standing root were investigated at systemic and pulmonary pressures in vitro. METHODS: Ten fresh pulmonary and aortic roots (anulus diameter, 20-25 mm) were tested in a pulsatile flow simulator. Five free-sewn pulmonary valves were implanted in aortic roots in the subcoronary position, and 5 pulmonary roots were implanted as free-standing roots. The external diameter of the roots was measured at the sinotubular junction in a pressure range of 0 to 120 mm Hg. The transvalvular gradient and regurgitation were measured, and the effective orifice area was calculated. The leaflet motion was recorded on video tape. RESULTS: The fresh pulmonary roots were more compliant than their aortic counterparts (33% +/- 3. 0% vs 7% +/- 1.5% with dilatation at 0-30 mm Hg and 46% +/- 8.4% vs 35% +/- 7.8% with dilatation at 0-120 mm Hg). The pulmonary roots had a lower pressure drop at systemic than at pulmonary pressures. The pressure drops of the pulmonary roots were also lower than those of the aortic roots in the systemic pressure range. The leaflet opening of the pulmonary valve was triangular, with low bending deformation at all pressures. Implanting the free-sewn pulmonary valve in the subcoronary position or the pulmonary root as a free-standing root did not affect the hydrodynamic parameters and leaflet motion adversely. CONCLUSION: The pulmonary valve and root could easily withstand aortic pressures in vitro. A biphasic dilatation curve ensures that higher pressures did not overdilate the pulmonary root. Moreover, valve performance was better at systemic pressures.

Animals↗
PubMed2003

Biomolecular hydration: from water dynamics to hydrodynamics.

Thermally driven rotational and translational diffusion of proteins and other biomolecules is governed by frictional coupling to their solvent environment. Prediction of this coupling from biomolecular structures is a longstanding biophysical problem, which cannot be solved without knowledge of water dynamics in an interfacial region comparable to the dry protein in volume. Efficient algorithms have been developed for solving the hydrodynamic equations of motion for atomic-resolution biomolecular models, but experimental diffusion coefficients can be reproduced only by postulating hundreds of rigidly bound water molecules. This static picture of biomolecular hydration is fundamentally inconsistent with magnetic relaxation dispersion experiments and molecular dynamics simulations, which both reveal a highly dynamic interface where rotation and exchange of nearly all water molecules are several orders of magnitude faster than biomolecular diffusion. Here, we resolve this paradox by means of a dynamic hydration model that explicitly links protein hydrodynamics to hydration dynamics. With the aid of this model, bona fide structure-based predictions of global biomolecular dynamics become possible, as demonstrated here for a set of 16 proteins for which accurate experimental rotational diffusion coefficients are available.

Animals↗
PubMed2006

Hydrodynamic studies on the quaternary structure of recombinant mouse Purbeta.

Purbeta is a gene regulatory factor belonging to a family of highly conserved nucleic acid-binding proteins related by their ability to preferentially bind single-stranded DNA or RNA sequences rich in purine nucleotides. In conjunction with Puralpha, Purbeta has been implicated in transcriptional and translational repression of genes encoding contractile proteins found in the heart and vasculature. Although several models of sequence-specific DNA recognition, strand separation, and activator inhibition by oligomeric Puralpha and Purbeta have been proposed, it is currently unclear whether protein-protein interaction is a prerequisite to, or a consequence of nucleic acid binding. In this study, a recombinant protein purification scheme was devised to yield homogenous mouse Purbeta devoid of nucleic acid. Recombinant Purbeta was then subjected to light scattering and analytical ultracentrifugation analyses to assess the size, shape, and oligomeric state of the purified protein in solution. Results of laser light scattering and sedimentation velocity experiments indicated that Purbeta reversibly self-associates in the absence of nucleic acid. Both approaches independently showed that the hydrodynamic shape of the Purbeta homodimer is markedly asymmetric and non-spherical. Sedimentation velocity analyses indicated that dimeric Purbeta has a sedimentation coefficient of 3.96 Svedberg, a frictional coefficient ratio (f/f(0)) of 1.60, and a hydrodynamic radius of 4.43 nm. These values were consistent with those determined by independent dynamic light scattering studies. Sedimentation equilibrium analyses confirmed that Purbeta self-associates in a reversible monomer-dimer equilibrium characterized by a K(d) = 1.13 +/- 0.27 microm.

Animals↗
PubMed1992

Blood flow hydrodynamic resistance in patients with ischaemic stroke or vascular encephalopathy and possibilities of its correction in vitro.

In order to determine the patient blood flow hydrodynamic properties in terms of the Toms-effect, the time blood flow was measured in special apparatus twice: (1) before and (2) after addition of poly(ethylene oxide) WSR-301 (Union Carbide, USA) in concentration of 2 x 10(6) g/ml of blood sample (50 ml with 500 units of heparin) taken from 26 patients with acute ischaemic stroke, 8 patients with vascular encephalopathy after stroke, 5 patients with vascular encephalopathy following atherosclerosis with or without arterial hypertension. The blood samples taken from 8 healthy persons formed the control group. Haematocrit (HCT) and asymptotic blood viscosity were studied also. It was established that hydrodynamic blood flow resistance (HBFR) did not depend on HCT and viscosity, but was significantly higher in all patient groups than in normal persons (p less than 0.05). Addition of polymer solution decreased HBFR of patient blood more intensively that in the control group. We believe that it indicates an insufficiency of an unidentified factor in native human blood.

Adult↗
PubMedDate not supplied

Application of a hydrodynamic model to microencapsulation by coacervation.

The role of the hydrodynamic conditions in determining the characteristics of microcapsules made by coacervation was investigated in this study. The model proposed by Armenante and Kirwan, regarding the mass transfer to microcapsules in a turbulent agitated system, was applied. The working hypothesis was that the microcapsules are formed in microeddies generated by the agitation source. The dimensions of the microeddies, calculated in the vicinity of the agitation source according to Armenante and Kirwan, depend on the physical properties of the liquid medium and are inversely proportional to the power exchanged from the agitation source of the system. The power was determined according to the hydrodynamic rules developed by Rushton et al. The experimental results confirmed the hypothesis of the model. Indeed, a good relationship was found between the calculated size of the microeddies and the measured diameter of the microcapsules. Moreover, the distribution error (the standard deviation of the microcapsule size frequency distribution curve) was found to be proportional to the mean diameter value of the microcapsules and microeddies. This can be explained considering that the microeddies diameter increases by moving away from the agitation source and, consequently, a distribution of microeddies of difference sizes is present in the medium. The distribution error, which represents the difference between the smaller and the larger diameters, is inversely proportional to the exchanged power and, consequently, proportional to the mean diameter.

Drug Compounding↗
PubMed2004

A prospective study on the clinical effect of surgical treatment of normal pressure hydrocephalus: the value of hydrodynamic evaluation.

The effect of surgical treatment of patients with normal pressure hydrocephalus (NPH) is reported to be variable. Candidates for surgery have often been selected using hydrodynamic tests; however, the predictive value of such tests remains uncertain. Seventeen patients with idiopathic NPH underwent continuous computerized intracranial pressure (ICP) monitoring and a steady state lumbar infusion test determining the resistance to cerebrospinal outflow (R(out)). The patients were treated surgically and clinically re-examined approximately 6 months postoperatively using a new NPH score. The effect of surgical treatment was good. The R(out) was positively correlated with the clinical state of the patients before treatment. After surgery, the R(out) correlated well with the improvement in gait and NPH score. Ventricular size was negatively correlated with hydrodynamic variables before treatment. Surgery reduced the ventricular size only slightly and the degree of reduction was linked to the R(out). ICP measurements could not predict outcome in NPH cases.

Adult↗
PubMed2006

The effect of solid surface tension and exposure to elevated hydrodynamic shear on Pseudomonas fluorescens biofilms grown on modified titanium surfaces.

The solid surface tension of titanium was varied by using organosilane monolayers of various terminations, minimising differences in other material properties. Both the quantity of Pseudomonas fluorescens biofilms grown on the modified surfaces, and the percentage of biofilm remaining after exposure to hydrodynamic shear stress, varied significantly as a function of solid surface tension. The quantity of biofilm was less on chloropropyl-terminated surfaces than on an alkyl-terminated surfaces. However, the percentage of biofilm remaining after exposure to hydrodynamic shear stress (which depends on the adhesion and cohesion strengths of the biofilm) was less for the alkyl-terminated surface than for the chloropropyl-terminated surface, for one of the two sample sets analysed. These results demonstrate the importance of differentiating between the quantity of biofilm on a surface and the adhesion and cohesion strength of the biofilm, and may help explain discrepancies in the existing literature regarding the effect of solid surface tension on the propensity of a surface for microfouling.

Biofilms↗
PubMed2005

Effects of hydrodynamic conditions on OH radical production at Ti/Pt anodes during electrochemical treatment.

The effects of hydrodynamic conditions on the production of hydroxyl radicals (*OH) during electrochemical treatment using a titanium coated by platinum anode and a stainless steel cathode are discussed in this paper. The sample used was ultra-pure water containing 200 mM of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). The amount of *OH for treatment was measured using electron spin resonance spectrometry coupled with DMPO spin trapping. Under constant hydrodynamic conditions, the production rate of the *OH spin adduct (DMPO-OH) increased with the terminal potential. This result was caused by the change in the electric current density at the anode, which was proportional to the rate of production of DMPO-OH. Increasing the linear velocity of water in an electrolytic cell promoted the production of DMPO-OH by two effects, namely, by the enhancement of ion transportation and the promotion of DMPO transfer from the bulk to the anode. The former effect emerged when the DMPO concentration near the anode was not insignificant in comparison with the DMPO concentration in the bulk, that is, when the overall rate-determining step was the electron transfer at the anode. The latter effect emerged when the DMPO concentration near the anode was much lower than the DMPO concentration in the bulk, that is, when the overall rate-determining step was the diffusion of DMPO from the bulk to the anode. In addition, the latter effect was found to be proportional to the square root of the linear velocity of water in the electrolytic cell.

Electrodes↗
PubMed2006

Kinetics, mass transfer and hydrodynamics in a packed bed aerobic reactor fed with anaerobically treated domestic sewage.

This study presents an assessment of the kinetic, mass transfer and hydrodynamic parameters of a pilot-scale fixed bed reactor containing immobilized biomass in polyurethane matrices and fed with the effluent of a horizontal-flow fixed bed anaerobic reactor, which was used to treat domestic sewage. It was found that the liquid-solid and intra-particle mass transfer resistances significantly affected the overall oxygen consumption rate and that mechanical agitation could minimize such resistances. The volumetric oxygen transfer coefficient (kLa) values for superficial air velocities between 8.4 cm min(-1) and 57.0 cm min(-1) varied from 20.8 h(-1) to 58.8 h(-1) for tap water, and 16.8 h(-1) to 53.0 h(-1) for the anaerobic pre-treated effluent. The intrinsic oxygen uptake rate was estimated to be 19.9 mgO2 gVSS(-1) h(-1). A first-order kinetic model with residual concentration was considered to adequately represent the COD removal rate, whereas nitrogen conversion was considered to be well represented by a model of pseudo-first-order reaction in series. It was also found that the ammonium conversion to nitrite was the limiting step of the overall nitrogen conversion rate. The hydrodynamic behavior of the reactor was represented by three to four completely mixed reactors in series.

Bacteria, Aerobic↗
PubMed2001

Hydrodynamic damage to animal cells.

Animal cells are affected by hydrodynamic forces that occur in culture vessel, transfer piping, and recovery operations such as microfiltration. Depending on the type, intensity, and duration of the force, and the specifics of the cell, the force may induce various kinds of responses in the subject cells. Both biochemical and physiological responses are observed, including apoptosis and purely mechanical destruction of the cell. This review examines the kinds of hydrodynamic forces encountered in bioprocessing equipment and the impact of those forces on cells. Methods are given for quantifying the magnitude of the specific forces, and the response thresholds are noted for the common types of cells cultured in free suspension, supported on microcarriers, and anchored to stationary surfaces.

Animals↗
PubMed2004

Effect of hydrodynamic environment on tablets dissolution rate.

The main objective of this research was to develop an experimental method to apply well-defined flow fields to solid dosage forms, to study the rate process underlying tablet dissolution, and to better understand the role of external hydrodynamic condition on mass transfer rate and film thickness during dissolution. Two drugs models, Theophylline (class 1) and Naproxen (class 2), were selected and formulated into conventional tablets containing 105 mg Theophylline or 300 mg Naproxen using the wet granulation method. Tablets were tested for dissolution using both the basket and paddle methods at different rotational speed of 25, 50, 75, and 100 rpm. In general, the paddle method gave higher dissolution rates than the basket method and as the velocity of rotation was increased, drug release was also increased. Six different paddles and a tablet holder were designed and used to test dissolution rate. The rate of dissolution was dependent on the tablet surface area exposed to the dissolution medium, and on the shape, diameter, and area of the paddles used. Theophylline tablets showed increased mass transfer rate and decreased film thickness as basket rotation speed was increased. At 25 rpm, the mass transfer coefficient was 0.684 x 10(-4) cm/sec and film thickness was 12.003 x 10(-2) cm; at 100 rpm, the mass transfer coefficient was 3.884 x 10(-4) cm/sec and film thickness was 2.114 x 10(-2) cm. Paddle values tested at the same speed showed higher mass transfer coefficient and lower film thickness for Theophylline and Naproxen tablets. P values obtained by modification of the Stokes-Einstein equation showed that diffusion is the rate-limiting step to drug release and not mass transfer. This study demonstrated that hydrodynamic condition, type of dissolution testing used, and design of the paddles have an effect on dissolution rate, mass transfer rate, and the film thickness underlying the dissolution process.

Chemistry, Pharmaceutical↗
PubMed2006

A hydrodynamics approach to the evolution of multicellularity: flagellar motility and germ-soma differentiation in volvocalean green algae.

During the unicellular-multicellular transition, there are opportunities and costs associated with larger size. We argue that germ-soma separation evolved to counteract the increasing costs and requirements of larger multicellular colonies. Volvocalean green algae are uniquely suited for studying this transition because they range from unicells to multicellular individuals with germ-soma separation. Because Volvocales need flagellar beating for movement and to avoid sinking, their motility is modeled and analyzed experimentally using standard hydrodynamics. We provide comparative hydrodynamic data of an algal lineage composed of organisms of different sizes and degrees of complexity. In agreement with and extending the insights of Koufopanou, we show that the increase in cell specialization as colony size increases can be explained in terms of increased motility requirements. First, as colony size increases, soma must evolve, the somatic-to-reproductive cell ratio increasing to keep colonies buoyant and motile. Second, increased germ-soma specialization in larger colonies increases motility capabilities because internalization of nonflagellated germ cells decreases colony drag. Third, our analysis yields a limiting maximum size of the volvocalean spheroid that agrees with the sizes of the largest species known. Finally, the different colony designs in Volvocales reflect the trade-offs between reproduction, colony size, and motility.

Biological Evolution↗
PubMed2006

A novel hydrodynamic approach to the treatment of coronary artery disease.

AIMS: During severe coronary stenosis, capillary resistance increases. Drag-reducing polymers (DRPs) are blood-soluble macromolecules that reduce vascular resistance, possibly by altering blood hydrodynamics and rheology. Thus, we hypothesized that DRPs would enhance myocardial perfusion distal to a severe coronary stenosis. METHODS AND RESULTS: A flow-limiting left anterior descending (LAD) coronary artery stenosis was created in 12 open chest dogs. Coronary driving pressure, flow, trans-stenotic gradient, and radiolabelled microsphere myocardial perfusion were measured. Myocardial contrast echocardiography was performed and videointensity vs. pulsing interval data in the LAD and left circumflex beds were used to derive red cell velocity and capillary volume. Relative to baseline, the stenosis decreased LAD bed capillary volume (P = 0.019) and red blood cell velocity (P = 0.010). Intravenous DRP (polyethylene oxide, 2.5 ppm) decreased LAD microvascular resistance (P = 0.003) and increased microsphere flow (P = 0.009), capillary volume (P = 0.0006), and red cell velocity (P = 0.007) despite the presence of a severe stenosis. DRP did not alter blood viscosity. CONCLUSIONS: DRPs improve perfusion to myocardium subserved by a flow-limiting coronary stenosis by decreasing microvascular resistance through an increase in capillary volume. Primary modulation of blood hydrodynamics and rheology to reduce microvascular resistance offers a novel approach to the treatment of ischaemic coronary syndromes.

Animals↗
PubMed2004

Anti-tumor effects of naked plasmid DNA using a hydrodynamics-based procedure.

High levels of foreign gene expression in mouse hepatocytes can be achieved by the rapid injection of a large volume of naked plasmid (pDNA) into animals via the tail vein, the so-called hydrodynamics-based procedure. In this study, we evaluated the efficacy of hydrodynamics-based tumor necrosis factor alpha (TNFalpha) transfer for tumor treatment, in which the naked pDNA encoding TNFalpha was administered into the tail vein following a intravenous injection of B16 melanoma cells. The mice treated with TNFalpha-expressing pDNA displayed a profound reduction in lung metastasis.

Animals↗
PubMed1999

In vitro effectiveness study for hydrodynamic thrombectomy devices of the second generation.

RATIONALE AND OBJECTIVES: To determine the efficacy of clot removal and the amount of applied saline and aspirated fluid and to compare procedure-related particle embolization for the hydrodynamic thrombectomy devices the LF 140 Angiojet (LF 140), the double-lumen Hydrolyser (double HL), and the triple-lumen Hydrolyser (triple HL) in an in vitro flow model. METHODS: Thrombectomy of clots (n = 42) from 7-day-old porcine blood (9.8 g) was performed with the LF 140, the double HL, and the triple HL in a flow model (flow 1 L/min) made of silicone tubes (7 mm inner tube diameter). All catheters were used according to the manufacturer's recommendations. RESULTS: Mean time of thrombectomy ranged from 20 seconds (triple HL) to 58 seconds (LF 140, P < 0.05). Only for the triple HL was remaining thrombus found within the tubes (41 mg). None of the tested devices worked isovolumetrically: the mean ratio of applied saline and aspirated fluid for the devices ranged from 0.79 (triple HL) to 0.89 (double HL, P < 0.05). Mean embolus weight and percentage of embolism from original thrombus were 675 mg/6.7% (LF 140, P < 0.05), 38 mg/0.4% (double HL), and 26 mg/0.3% (triple HL). CONCLUSIONS: Thrombectomy time and embolus weight depend on the device chosen. The ratio of applied to aspirated fluid, indicating the capability to work nearly isovolumetrically, is acceptable for all tested devices. In vitro, the triple HL seems to be the most appropriate device for rapid mechanical, hydrodynamic thrombectomy. Because of the high in vitro particle embolization rate, the LF 140 seems to be strictly limited to small-caliber vessels.

Animals↗
PubMed1999

Enhancement of in vitro effectiveness for hydrodynamic thrombectomy devices. Simultaneous high-pressure rt-PA application.

RATIONALE AND OBJECTIVES: To determine the efficacy of simultaneous high-pressure recombinant tissue plasminogen activator (rt-PA) application for clot removal and procedure-related peripheral particle embolization for the hydrodynamic thrombectomy devices LF 140 AngioJet (LF 140) and triplelumen Hydrolyser (triple HL) in an in vitro flow model. METHODS: Thrombectomy of clots (n = 47) from 5-day-old human blood (8.9-9.7 g) was performed with the LF 140 and the triple HL, each with and without simultaneous rt-PA (9.97-12.59 g) application in a flow model (flow 1 liter/min) made of silicone tubes (7 mm inner tube diameter). All catheters were used according to the manufacturer's recommendations. RESULTS: The triple HL revealed no statistically significant performance differences with additional rt-PA. For the LF 140, mean thrombectomy time ranged from 23.5 sec (with rt-PA) to 33.5 sec (P = 0.05). The ratio of peripheral embolus weight to thrombus weight was reduced from 2.12% to 0.46% (rt-PA; P = 0.05). None of the tested devices had an isovolumetric performance; the mean ratio of applied saline to aspirated fluid for the devices were different from one, ranging from 0.89 to 0.92 (rt-PA) for the triple HL and from 0.43 to 0.52 (rt-PA) for the LF 140. No significant differences for remaining thrombus within the tubes were found. CONCLUSIONS: Simultaneous rt-PA-enhanced hydrodynamic thrombectomy is feasible in vitro. This combination reduces the time for thrombectomy and procedure-related peripheral particle embolization for the LF 140. No effect could be demonstrated for the triple HL in an in vitro flow model. It remains unclear whether this procedure is effective in vivo. It seems likely that the incidence of fibrinolysis-associated complications may increase in vivo.

Humans↗
PubMed2004

Kinematics and hydrodynamics of linear acceleration in eels, Anguilla rostrata.

The kinematics and hydrodynamics of routine linear accelerations were studied in American eels, Anguilla rostrata, using high-speed video and particle image velocimetry. Eels were examined both during steady swimming at speeds from 0.6 to 1.9 body lengths (L) per second and during accelerations from -1.4 to 1.3 L s(-2). Multiple regression of the acceleration and steady swimming speed on the body kinematics suggests that eels primarily change their tail-tip velocity during acceleration. By contrast, the best predictor of steady swimming speed is body wave speed, keeping tail-tip velocity an approximately constant fraction of the swimming velocity. Thus, during steady swimming, Strouhal number does not vary with speed, remaining close to 0.32, but during acceleration, it deviates from the steady value. The kinematic changes during acceleration are indicated hydrodynamically by axial fluid momentum in the wake. During steady swimming, the wake consists of lateral jets of fluid and has minimal net axial momentum, which reflects a balance between thrust and drag. During acceleration, those jets rotate to point downstream, adding axial momentum to the fluid. The amount of added momentum correlates with the acceleration, but is greater than the necessary inertial force by 2.8+/-0.6 times, indicating a substantial acceleration reaction.

Acceleration↗
PubMed2004

Lattice Boltzmann algorithm for three-dimensional liquid-crystal hydrodynamics.

We describe a lattice Boltzmann algorithm to simulate liquid-crystal hydrodynamics in three dimensions. The equations of motion are written in terms of a tensor order parameter. This allows both the isotropic and the nematic phases to be considered. Backflow effects and the hydrodynamics of topological defects are naturally included in the simulations, as are viscoelastic effects such as shear-thinning and shear-banding. We describe the implementation of velocity boundary conditions and show that the algorithm can be used to describe optical bounce in twisted nematic devices and secondary flow in sheared nematics with an imposed twist.

Journal Article↗