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PubMed1988

Review of hydrodynamic principles for the cardiologist: applications to the study of blood flow and jets by imaging techniques.

An understanding of the basic concepts of the physics of blood flow is of vital importance to the cardiologist as he or she attempts to utilize new blood flow imaging modalities, such as Doppler ultrasound and nuclear magnetic resonance imaging. Concepts such as the Bernoulli equation and its limitations, the continuity equation and volume flow calculations and the theory of free and confined jets have applications in cardiac blood flow-related problems. For example, mitral regurgitant flow may be treated with the free jet theory. Aortic stenosis results in confined jet flow. It is important that the cardiologist understand the basic principles behind these hydrodynamic concepts so that he or she can use them in appropriate applications. The limitations of the simplification of complex hydrodynamic relations that are used clinically need to be clearly understood so that these simplified principles are not used improperly or used to draw oversimplified conclusions.

Blood Circulation↗
PubMed1991

Mass analysis of bacteriophage T4 proheads and mature heads by scanning transmission electron microscopy and hydrodynamic measurements.

Quantitative mass analysis of bacteriophage T4 proheads by scanning transmission electron microscopy (STEM) revealed a mass of 79.5 +/- 0.6 MDa, while hydrodynamic measurements yielded a prohead mass of about 80 MDa. This is 25% less than the prohead mass deduced from its polypeptide composition, and this finding implies that the bacteriophage T4 prohead is built of fewer polypeptide copies than previously reported. In contrast, the mass of mature heads measured by STEM, 194 +/- 2 MDa, is in agreement with previous mass measurements of DNA and protein content, and it is consistent with the previously determined stoichiometry. This good agreement of average STEM values for proheads and mature heads with corresponding hydrodynamic measurements suggests that STEM allows faithful evaluation of the masses of large supramolecular assemblies (i.e., greater than or equal to 200 MDa) such as whole viruses or cellular organelles.

Formaldehyde↗
PubMed2006

The use of the hydrodynamic HBV animal model to study HBV biology and anti-viral therapy.

A simple reproducible and versatile small animal model for hepatitis B virus (HBV) infection is still unavailable. We have generated a simple transient liver-targeted transgenic mouse. Hydrodynamics tail vein injection of a head-to-tail dimer of adw HBV genome (pHBVadwHTD) into immunocompetent mice generated HBsAg and HBeAg expression in both serum and hepatocytes, followed by seroconversion. The injection of pHBVadwHTD into SCID mice generated prolonged HBsAg and HBeAg antigenemia and HBV viremia. Our results demonstrate that hydrodynamic injection of naked DNA could support the generation of HBV particles. We used this model for the assessment of anti-viral agents. Administration of our human monoclonal antibodies, HBV-Ab17(XTL) and HBV-Ab19(XTL), as well as Lamivudine (3TC) treatment suppressed HBV viremia. The model presented herein supports long and stable expression of HBV and will enable determination of various biological questions related to HBV life cycle, mutants and could enhance the development of anti-viral reagents.

Journal Article↗
PubMed2004

Effect of electrostatic, hydrodynamic, and Brownian forces on particle trajectories and sieving in normal flow filtration.

Particle deposition and fouling are critical factors governing the performance of microfiltration and ultrafiltration systems. Particle trajectories were evaluated by numerical integration of the Langevin equation, accounting for the combined effects of electrostatic repulsion, enhanced hydrodynamic drag, and Brownian diffusion. In the absence of Brownian forces, particles are unable to enter the membrane pores unless the drag associated with the filtration velocity can overcome the electrostatic repulsion. Brownian forces significantly alter this behavior, allowing some particles to enter the pore even at low filtration velocities. The average particle transmission, evaluated from the probability of having a particle enter the pore, increases with increasing filtration velocity due to the greater hydrodynamic drag force on the particle. These results provide important insights into particle behavior in membrane systems.

Journal Article↗
PubMed2005

Dynamic wetting: hydrodynamic or molecular-kinetic?

The dynamic wetting behavior of simple liquids (water, glycerin, formamide, ethylene glycol, and a mixture of water and ethylene glycol) and polydimethylsiloxane (PDMS) oils with different viscosities has been investigated. The hydrodynamic, molecular-kinetic, and combined molecular-hydrodynamic models have been applied to the experimental results to evaluate the models' adequacy. Our work suggests that the molecular displacement, i.e., the adsorption and desorption process, seems to be dominant for the simple liquids investigated. For polydimethylsiloxanes, our work suggests that none of the evaluated models is sufficient to explain the experimentally observed dependence of the dynamic contact angle on contact velocity. This work, to the best of our knowledge, provides the first extensive comparison of the three models with experimental data over a wide range of viscosity. In addition, we have investigated the contact angle hysteresis and conclude that it is a strong function of the contact speed, the interactions between the fluids and the substrate, and the fluid viscosity.

Journal Article↗
PubMed2004

Solution structure, dynamics, and hydrodynamics of the calcium-bound cross-reactive birch pollen allergen Bet v 4 reveal a canonical monomeric two EF-hand assembly with a regulatory function.

Birch pollinosis is one of the prevailing allergic diseases. In all, 5-20% of birch pollinotics mount IgE antibodies against the minor birch pollen allergen Bet v 4, a Ca2+-binding polcalcin. Due to IgE cross-reactivity among the polcalcins these patients are polysensitized to various plant pollens. Determination of the high-resolution structure of holo Bet v 4 by heteronuclear NMR spectroscopy reveals a canonical two EF-hand assembly in the open conformation with interhelical angles closely resembling holo calmodulin. The polcalcin-specific amphipathic COOH-terminal alpha-helix covers only a part of the hydrophobic groove on the molecular surface. Unlike the polcalcin Phl p 7 from timothy grass, which was recently shown to form a domain-swapped dimer, the hydrodynamic parameters from NMR relaxation, NMR translational diffusion, and analytical ultracentrifugation indicate that both apo and holo Bet v 4 are predominantly monomeric, raising the question of the physiological and immunological significance of the dimeric form of these polcalcins, whose physiological function is still unknown. The reduced helicity and heat stability in the CD spectra, the poor chemical shift dispersion of the NMR spectra, and the slightly increased hydrodynamic radius of apo Bet v 4 indicate a reversible structural transition upon Ca2+ binding, which explains the reduced IgE binding capacity of apo Bet v 4. The remarkable structural similarity of holo Bet v 4 and holo Phl p 7 in spite of different oligomerization states explains the IgE cross-reactivity and indicates that canonical monomers and domain-swapped dimers may be of similar allergenicity. Together with the close structural homology to calmodulin and the hydrophobic ligand binding groove this transition suggests a regulatory function for Bet v 4.

Allergens↗
PubMed2004

Small aortic annulus: the hydrodynamic performances of 5 commercially available bileaflet mechanical valves.

OBJECTIVE: Hemodynamic performances of mechanical valve prostheses in patients with aortic valve stenosis and a small aortic annulus are crucial. We analyzed the in vitro hydrodynamics of 5 currently available bileaflet mechanical prostheses that fitted a 21-mm-diameter valve holder of a Sheffield pulse duplicator. METHODS: Three samples of 5 high-performance production-quality prostheses, including the sewing ring cuffs, were tested in the aortic chamber of a Sheffield pulse duplicator. Sizes of the prostheses fitting the 21-mm valve holder were as follows: 18-mm ATS, 19-mm SJM Regent, 19-mm Sorin Bicarbon Slimline, 19-mm On-X, and 21-mm Carbomedics Top Hat. The tests were carried out at a fixed pulse rate (70 beats/min) and at increasing cardiac outputs of 2, 4, 5, and 7 L/min. Each valve was tested 10 times for each different cardiac output. This resulted in a total of 40 tests for each valve and 120 tests for each valve model. The aortic pressure was set at 120/80 mm Hg (mean pressure, 100 mm Hg) throughout the experiment for all cardiac outputs. Forward flow pressure decrease, total regurgitant volume, closing and leakage volumes, effective orifice area, and stroke work loss were recorded while the valve operated under each cardiac output. RESULTS: The SJM Regent valve and the Sorin Bicarbon Slimline prosthesis showed the lowest mean and peak gradients at increasing cardiac outputs. The closure volume was higher for the SJM Regent and Sorin Bicarbon Slimline prostheses, unlike with the ATS prosthesis at 7 L/min of cardiac output. The ATS and SJM Regent prostheses showed the largest regurgitant volume, whereas the Sorin Bicarbon Slimline prosthesis showed the lowest regurgitant volume. The calculated effective orifice area and stroke work loss were significantly better with the SJM Regent and Sorin Bicarbon Slimline prostheses. CONCLUSION: Assuming that the 21-mm valve holder in which all the tested prostheses were accommodated is comparable with a defined aortic valve size, this hydrodynamic evaluation model allowed us to compare the efficiency of currently available valve prostheses, and among these, the SJM Regent and the Sorin Bicarbon Slimline exhibited the best performances.

Aortic Valve↗
PubMed2006

Small aortic annulus: the hydrodynamic performances of 5 commercially available tissue valves.

BACKGROUND: In vivo comparison of the performance of heart valve prostheses is confounded by several factors, such as different nominal size, patients' characteristics and hemodynamics, surgical techniques, and study design. The aim of this study was to compare the in vitro hydrodynamic performances of 5 different tissue valves that would fit a 21-mm-diameter valve holder of the Sheffield pulse duplicator. METHODS: Three samples of 5 supra-annular production-quality tissue valves, including the sewing ring cuffs, were tested in the aortic chamber of the Sheffield pulse duplicator. The prostheses fitting a 21-mm valve holder, which is comparable with a 21-mm aortic annulus, were as follows: 20-mm Sorin Soprano, 21-mm Carpentier-Edwards Magna, 21-mm SJM-Biocor-Epic-Supra, 21-mm Medtronic Mosaic, and 23-mm Mitroflow. The tests were carried out at a fixed pulse rate (70 beats/min) and at increasing cardiac outputs of 2, 4, 5, and 7 L/min. Each valve was tested 10 times for each different cardiac output. This resulted in a total of 40 tests for each valve and 120 tests for each valve model. Forward flow pressure decrease, effective orifice area, stroke work loss, and total regurgitant, closing, and leakage volumes were recorded while the valve operated under each cardiac output. RESULTS: Pericardial valves showed significantly lower transvalvular gradients than porcine valves, unlike the SJM-Biocor-Epic-Supra valve at 2 L/min of cardiac output. Although the Carpentier-Edwards Magna valve provided the best performance at 2 and 4 L/min, the Mitroflow valve exhibited the lowest mean and peak gradients at 5 to 7 L/min. Total regurgitant and leakage volumes were higher for the Carpentier-Edwards Magna valve and lower for the SJM-Biocor-Epic-Supra and Mitroflow valves. Between 2 and 4 L/min, the calculated effective orifice area and stroke work loss were better for the Carpentier-Edwards Magna valve, whereas between 5 and 7 L/min, they were significantly superior with the Mitroflow prosthesis. Among the porcine bioprostheses, the SJM-Biocor-Epic-Supra valve showed significantly better results when compared with the Medtronic Mosaic valve at each cardiac output. CONCLUSION: Assuming that the valve holder is comparable with a defined aortic annulus of 21 mm in which a spread of supra-annular tissue valves could be fitted, this hydrodynamic evaluation model allows comparison of the efficiency of currently available bioprostheses with a definite tissue annulus diameter. Pericardial valves exhibited the best performances, and the Mitroflow valve showed the lowest gradients and stroke work loss at increasing cardiac output.

Aortic Valve↗
PubMed2004

Effect of biodeposits from mussel culture on macroinvertebrate assemblages at sites of different hydrodynamic regime.

The present study examined for differences in macroinvertebrate assemblage composition inside and outside of mussel farm sites experiencing different hydrodynamic regimes. Multivariate analysis revealed that there were significant differences in macroinvertebrate assemblage composition (averaged across seasons) between samples taken inside and outside of the two relatively low energy sites, whilst no such difference was observed for the relatively high energy site. Taxa that best discriminated between the dissimilarities observed in macroinvertebrate assemblage composition inside and outside farms were principally polychaetes (more abundant inside) and ophiuroids (more abundant outside). Sediment total organic matter and number of mussel shells were the parameters that best explained the difference in macroinvertebrate assemblage observed at the two relatively sheltered farm study sites. No taxa or environmental variables were particularly good at discriminating or explaining differences observed inside and outside the relatively high energy farm site. The present study indicates there is a relationship between the hydrodynamic regime of a farm site, organic enrichment of seabed sediments by mussel biodeposits, and a subsequent modification of the macroinverebrate assemblages. This finding has implications for the site selection of mussel farms in coastal environments.

Animals↗
PubMed2005

SOMO (SOlution MOdeler) differences between X-Ray- and NMR-derived bead models suggest a role for side chain flexibility in protein hydrodynamics.

Reduced numbers of frictional/scattering centers are essential for tractable hydrodynamic and small-angle scattering data modeling. We present a method for generating medium-resolution models from the atomic coordinates of proteins, basically by using two nonoverlapping spheres of differing radii per residue. The computed rigid-body hydrodynamic parameters of BPTI, RNase A, and lysozyme models were compared with a large database of critically assessed experimental values. Overall, very good results were obtained, but significant discrepancies between X-ray- and NMR-derived models were found. Interestingly, they could be accounted for by properly considering the extent to which highly mobile surface side chains differently affect translational/rotational properties. Models of larger structures, such as fibrinogen fragment D and citrate synthase, also produced consistent results. Foremost among this method's potential applications is the overall conformation and dynamics of modular/multidomain proteins and of supramolecular complexes. The possibility of merging data from high- and low-resolution structures greatly expands its scope.

Algorithms↗
PubMed2004

Hydrodynamic damping of a magnetically oscillated cantilever close to a surface.

We studied the frequency response of a magnetically driven atomic force microscope (AFM) cantilever close to a sample surface in liquids. Amplitude-frequency (tuning) curves showed pronounced differences in dependence on the tip-sample separation (from 1 to 50 microm), with significant shifts of the resonance peak. A model was developed in which the cantilever was described in a full shape manner and the hydrodynamic forces acting on the cantilever were approximately calculated. The slight inclination of the cantilever to the surface (alpha approximately 15 degrees) leads to a force profile along the cantilever. Therefore, the mathematical problem can be strictly solved only numerically. For an approximate analytical solution, the hydrodynamic force profile was approximated by a constant force along the cantilever for large separations and by a point force acting on the tip of the cantilever for small separations. The theoretical results calculated within this model agreed well with the experimental data and allowed to determine the cantilever mass in liquid M*, the joint mass at the tip end m*t, and the coefficient of viscous interaction of the cantilever with free liquid, gamma(infinity).

Journal Article↗
PubMed2005

A review and assessment of hydrodynamic cavitation as a technology for the future.

In the present work, the current status of the hydrodynamic cavitation reactors has been reviewed discussing the bubble dynamics analysis, optimum design considerations, design correlations for cavitational intensity (in terms of collapse pressure)/cavitational yield and different successful chemical synthesis applications clearly illustrating the utility of these types of reactors. The theoretical discussion based on the modeling of the bubble dynamics equations aims at understanding the design information related to the dependency of the cavitational intensity on the operating parameters and recommendations have been made for the choice of the optimized conditions of operating parameters. The design information based on the theoretical analysis has also been supported with some experimental illustrations concentrating on the chemical synthesis applications. Assessment of the hydrodynamic cavitation reactors and comparison with the sonochemical reactors has been done by citing the different industrially important reactions (oxidation of toluene, o-xylene, m-xylene, p-xylene, mesitylene, o-nitrotoluene, p-nitrotoluene, m-nitrotoluene, o-chlorotoluene and p-chlorotoulene, and trans-esterification reaction i.e., synthesis of bio-diesel). Some recommendations have also been made for the future work to be carried out as well as the choice of the operating conditions for realizing the dream of industrial scale applications of the cavitational reactors.

Computer Simulation↗
PubMed2005

Oxidation of alkylarenes using aqueous potassium permanganate under cavitation: comparison of acoustic and hydrodynamic techniques.

Various alkylarenes were oxidized to the corresponding aryl carboxylic acids using aqueous potassium permanganate under heterogeneous condition in the presence of hydrodynamic cavitation and the results of the reaction have been compared with the acoustic cavitation in terms of their energy efficiency. The rate of reaction was determined for each reaction. In the oxidation of p-xylene, seven times more product could be obtained in the case of hydrodynamic cavitation than in the case of acoustic cavitation. The reaction was found to be considerably accelerated at ambient temperature.

Alkylation↗
PubMed2005

Dynamics of cavitational bubbles and design of a hydrodynamic cavitational reactor: cluster approach.

In the present work, a cavity cluster of predetermined size has been considered to study the bubble dynamics in the hydrodynamic cavitation reactor. The effect of different operating and system parameters on the cavitational intensity has been numerically investigated. The yield of any cavitationally induced physical/chemical transformations depends not only on the collapse pressure of the cavities but also on the active volume of cavitation within the reactor. Empirical correlations have been developed to predict the collapse pressure and the active volume of cavitation as a function of different operating parameters based on the bubble dynamics studies. Recommendations are made for designing a cavitational reactor on the basis of the proposed empirical correlations. This work is a first step towards the designing and optimization of hydrodynamic cavitational reactor with cluster approach.

Journal Article↗
PubMed2004

Hydrodynamic behaviour and comparison of technologies for the removal of excess biomass in gas-phase biofilters.

The hydrodynamic behaviour of a biofilter fed toluene and packed with an inert carrier was evaluated on start-up and after long-term operation, using both methane and styrene as tracers in Residence Time Distribution experiments. Results indicated some deviation from ideal plug flow behaviour after 2-year operation. It was also observed that the retention time of VOCs gradually increased with time and was significantly longer than the average residence time of the bulk gas phase. Non-ideal hydrodynamic behaviour in packed beds may be due to excess biomass accumulation and affects both reactor modeling and performance. Therefore, several methods were studied for the removal of biomass after long-term biofilter operation: filling with water and draining, backwashing, and air sparging. Several flow rates and temperatures (20-60 degrees C) were applied using either water or different chemicals (NaOH, NaOCl, HTAB) in aqueous solution. Usually, higher flow rates and higher temperatures allowed the removal of more biomass, but the efficiency of biomass removal was highly dependent on the pressure drop reached before the treatment. The filling/draining method was the least efficient for biomass removal, although the treatment did basically not generate any biological inhibition. The efficiency of backwashing and air sparging was relatively similar and was more effective when adding chemicals. However, treatments with chemicals resulted in a significant decrease of the biofilter's performance immediately after applying the treatment, needing periods of several days to recover the original performance. The effect of manually mixing the packing material was also evaluated in duplicate experiments. Quite large amounts of biomass were removed but disruption of the filter bed was observed. Batch assays were performed simultaneously in order to support and quantify the observed inhibitory effects of the different chemicals and temperatures used during the treatments.

Biodegradation, Environmental↗
PubMed2005

Influence of internal biogas production on hydrodynamic behavior of anaerobic fluidized-bed reactors.

Predictive models for describing the hydrodynamic behavior (bed-expansion and bed-pressure gradient) of a three-phase anaerobic fluidized bed reactor (AFBR) was developed according to wake theory together with more realistic dynamic bed-expansion experiments (with and without internal biogas production). A reliable correlation equation for the parameter k (mean volume ratio of wakes to bubbles) was also established, which is of help in estimating liquid hold up of fluidized beds. The experimental expansion ratio of three-phase fluidized beds (E(GLS)) was approximately 18% higher than that of two-phase fluidized beds (E(LS)); whereas the experimental bed-pressure gradient of the former [(-DeltaP/H)(GLS)] was approximately 9.3% lower than that of the latter [(-DeltaP/H)(LS)]. Both the experimental and modeling results indicated that a higher superficial gas velocity (u(g)) gave a higher E(GLS) and a higher E(GLS) to E(LS) ratio as well as a lower (-DeltaP/H)(GLS) and a lower (-DeltaP/H)(GLS) to (-DeltaP/H)(LS) ratio. As for the operation stability of the AFBR, the sensitivity of u(g) to expansion height (H(GLS)) and (-DeltaP/H)(GLS) is between the sensitivity of superficial liquid velocity and biofilm thickness. The model predictions of E(GLS), (-DeltaP)(GLS), and (-DeltaP/H)(GLS) agreed well the experimental measurements. Accordingly, the predictive models accounting for internal biogas production described fairly well the hydrodynamic behavior of the AFBR.

Bacteria, Anaerobic↗
PubMed2000

The effect of sizing on the hydrodynamic parameters of the Medtronic freestyle valve in vitro.

BACKGROUND: An in vitro model has been established to investigate the effect of sizing on the hydrodynamic characteristics and leaflet motion of the Medtronic Freestyle valve. METHODS: The valves were tested in fresh porcine aortic roots. Two or three different sizes of valves were implanted in the same aortic root one after the other. The compliance of the fresh aortic and the composite roots was measured in the pressure range of 0 to 120 mm Hg, and the composite roots were then tested in a pulsatile flow simulator. The transvalvular gradient and degree of regurgitation were measured and the effective orifice area and performance index were calculated. Leaflet motion was recorded on video. RESULTS: The fresh aortic roots dilated by average 39.4% as the hydrostatic pressure rose from 0 to 120 mm Hg. Implantation of the Medtronic Freestyle valve did not change the distensibility of the aortic root significantly. The sizing protocol did not affect significantly the hydrodynamic performance. However, a significantly lower open leaflet bending deformation was found in the undersized valves. Regurgitation was found only at 2-mm undersized valves. CONCLUSIONS: Leaflet motion of the Medtronic Freestyle valve in vitro was best if 1 mm undersized, and this may be beneficial to long-term durability.

Aorta↗
PubMed2002

Hydrodynamic function of the second-generation mitroflow pericardial bioprosthesis.

BACKGROUND: The hydrodynamic function of the smaller size Mitroflow Synergy stented pericardial bioprostheses has been studied in an in vitro fresh tissue aortic root model and compared with previous studies of free-sewn bioprostheses. METHODS: Three valves of each of the sizes 19, 21, and 23 mm were sutured into fresh tissue aortic roots and tested in a pulsatile flow simulator using two different ventricular input impedance conditions. A high-speed camera was used to study the leaflet opening and closing configurations. Mean pressure difference as a function of root mean square forward flow, effective orifice area, regurgitant volumes, and total energy loss across the valves was measured. RESULTS: Mean pressure difference with respect to root mean square forward flow decreased as the valve size increased. Thus effective orifice area increased as the valve size increased. The open leaflet configuration images showed that all three sizes of Mitroflow valves had a large circular orifice with minimal open leaflet deformation. All valves closed competently with no visible leakage and no closed regurgitant volume. The Mitroflow valves showed better effective orifice areas compared with previously tested frame-mounted porcine bioprostheses but lower effective orifice areas compared with porcine stentless bioprostheses; however, the open leaflet bending deformation was better than for any of the previously tested bioprosthetic valves. CONCLUSIONS: The hydrodynamic function of the Mitroflow Synergy stented pericardial bioprosthesis shows potential for good in vivo hemodynamic performance. The good hemodynamic performance combined with relative ease of implantation technique makes the pericardial valve a good valve in the aortic position, particularly in older patients with small annuli.

Animals↗