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PubMed2004

Behaviour of biofilm systems under varying hydrodynamic conditions.

Heterotrophic biofilms were cultivated in long-term experiments in biofilm tube reactors. During the biofilm cultivation the substrate loading of glucose was kept constant while the hydrodynamic conditions were changed stepwise. To describe the behaviour of the biofilm structure under these varying flow conditions the mass transfer and transport at the bulk/biofilm interface and inside the biofilm was investigated with oxygen microelectrodes. Furthermore, the biofilm density was used to describe the biofilm compactness before and after the change of the hydrodynamic condition. The obtained results show that the biofilm density and also the substrate flux decreased with decreasing flow velocity in the bulk phase. Additionally the slope of the oxygen concentration profiles decreased and the thickness of the concentration boundary layer increased. On the other hand, increasing the flow velocity in the bulk phase led both to a higher biofilm density and a higher maximum substrate flux. The biofilm surface became more homogenous and the thickness of the concentration boundary layer decreased. The time for adaptation of the biofilm structure after changing the hydrodynamic conditions ranged between 1 and 3 weeks.

Biofilms↗

PubMedDate not supplied

[Hydrodynamics-based transfer of human apolipoprotein A-I gene into mice: study of factors involving an efficacy and duration of the transferred gene expression in animals' liver].

Human apolipoprotein A-I gene (apoA-I) plasmid expression vectors were transferred into mice by hydrodynamic injections into tail vein. Two types of expression vectors were used. First one -pCMVcapoAI contains cDNA of apo A-I driven by human cytomegalovirus early gene promoter (CMV). Second one--pAlg contains genomic locus of intron-containing apo A-I under control of own extended 5'-regulatory region (APOAI). Hydrodynamic intravenous injections of both expression vectors led to appearance of human apo A-I mRNA in the liver and human Apo A-I protein in the serum of injected mice. Dynamics of human Apo A-I content in the serum of mice injected by pCMVcapoAI and pAlg were different. When pCMVcapoAI was used, maximal concentration of human Apo A-I protein in the mouse serum was detected one day after injection with following decline to zero level during next two weeks. Under the same conditions injections of pAlg led to maximal level of human Apo A-I concentration in the mouse serum (up to 20 mkg/ml in some animals) on the 5th-7th day of experiment with following graduate decline during several months (human Apo A-I concentration in the serum of oldest analyzed mouse (6 months after injection) was about 25% of its maximal level in the same animal). Levels of human Apo A-I concentration in the mouse serum were compatible after injections of both expression vectors, in spite of much more strong activity of CMV promoter in comparison with APOAI in cultured human hepatoma cells HepG2. We ascribe the revealed difference in dynamics of human Apo A-I expression to delay of apo A-I transcription from pAlg vector, that was confirmed by nested RT-PCR. Significant level and long-term persistence of human Apo A-I in the serum of mice injected by pAlg could be explained by properties of APOAI or (and) exon-intron structure of genomic apo A-I gene. To test the role of APOAI in long-term expression of human Apo A-I in the mice we performed hydrodynamic injections of plasmid vectors containing cDNA of reporter gene encoding luciferase driven by variants of APOAI. No long-term expression of luciferase was found in the livers of injected mice. Therefore, our data suggest the role of exon-intron structure in maintaining of efficient and long-term expression of transferred human apo A-I.

Animals↗

PubMed2005

Influence of mimic cardiac rate on hydrodynamics of different mechanical prosthetic cardiac valves in vitro.

OBJECTIVE: To assess the influence of mimic cardiac rate on hydrodynamics of different mechanical prosthetic cardiac valves. METHODS: US-made CarboMedics bileaflet valve, China-made Jiuling bileaflet valve and C-L tilting disc valve were tested via a pulsatile flow simulator in the aortic position. Testing conditions were set at mimic cardiac rates of 55 bpm, 75 bpm, 100 bpm with a constant mimic cardiac output of 4 L/min. The mean pressure differences (deltaP), leakage volumes (L(E)V) and closing volumes (C(L)V) across each valve, and effective orifice areas (EOA) were analyzed. RESULTS: Within physiological range, deltaP, L(E)V, and C(L)V decreased as mimic cardiac rate increased, with a large extent of variance. EOA increased along with an increase in mimic cardiac rate. It was a different response in terms of cardiac rate alteration for different types of mechanical prosthetic cardiac valves. CONCLUSION: Mimic cardiac rate change affects hydrodynamics of mechanical prosthetic cardiac valves. Within physiological range, the hydrodynamic of prosthetic bileaflet valve is better than that of tilting disc valve.

Biomechanical Phenomena↗

PubMed2004

Hydrodynamic gene delivery of interleukin-22 protects the mouse liver from concanavalin A-, carbon tetrachloride-, and Fas ligand-induced injury via activation of STAT3.

Interleukin-22 (IL-22) is a recently identified T cell-derived cytokine whose biological significance remains obscure. Previously, we have shown that IL-22 plays a protective role in T cell-mediated hepatitis induced by Concanavalin A (Con A), acting as a survival factor for hepatocytes. In the present paper, we demonstrate that hydrodynamic gene delivery of IL-22 cDNA driven either by a liver-specific albumin promoter or a human cytomegalovirus (CMV) promoter results in IL-22 protein expression, STAT3 activation, and expression of several anti-apoptotic proteins, including Bcl-xL, Bcl-2, and Mcl-1 in the liver. Immunohistochemical analysis reveals that IL-22 protein expression is mainly detected in the cytoplasm of hepatocytes. Overexpression of IL-22 by hydrodynamic gene delivery significantly protects against liver injury, necrosis, and apoptosis induced by administration of Con A, carbon tetrachloride (CCl4), or the Fas agonist Jo-2 mAb. Western blot analyses show that overexpression of IL-22 significantly enhances activation of STAT3 and expression of Bcl-xL, Bcl-2, and Mcl-1 proteins in liver injury induced by Con A. In conclusion, hydrodynamic gene delivery of IL-22 protects against liver injury induced by a variety of toxins, suggesting the therapeutic potential of IL-22 in treating human liver disease.

Animals↗

PubMed2005

Mutated-leptin gene transfer induces increases in body weight by electroporation and hydrodynamics-based gene delivery in mice.

To investigate whether in vivo gene transfer causes leptin-antagonistic effects on food intake, animal body weight and fat tissue weight, the R128Q mutated-leptin gene, an R to Q substitution at position 128 of mouse leptin, was transferred into mouse liver and leg muscle by electroporation and hydrodynamics-based gene delivery. Mutated-leptin gene transfer by electroporation caused significant increases in body weight at 5 days and after (5.4% increase relative to control; p<0.05). Hydrodynamics-based gene delivery of the mutated-leptin gene also caused an increase in body weight (3.0% increase relative to control; p<0.05). Mutated-leptin gene transfer by electroporation significantly increased the tissue weight of epididymal white fat and neuropeptide Y mRNA expression in the hypothalamus compared with those of the control group 3 weeks after gene transfer (p<0.05). These results suggest that mutated-leptin gene transfer successfully produced leptin-antagonistic effects by modulating the central regulator of energy homeostasis. Also, the extent of leptin-antagonistic effects by electroporation was much higher than hydrodynamics-based gene delivery, with at least single gene transfer.

Adipose Tissue, Brown↗

PubMed2006

Effect of hydrodynamic environment on tablet dissolution using flow-through dissolution apparatus.

The main objective of this research is to investigate the principles underlying the dissolution process, study the phenomena of drug release in laminar flow, and better understand the effect of hydrodynamic condition on drug dissolution, in order to predict drug dissolution from a solid dosage form. Two drug models were selected, theophylline (Class I) and naproxen (Class II), and were formulated into conventional tablets containing 105 mg theophylline or 300 mg naproxen using wet granulation method. Additionally theophylline (105 mg) and naproxen (300 mg) matrices containing 30% hydroxypropylmethylcellulose (HPMC) polymer were prepared by direct compression and tested for dissolution using both USP II and IV dissolution apparatus. Tablets were tested for dissolution (USP IV) using different cell diameter, flow rate, and different position of the tablet inside the cell. In general, the drug dissolution at a given time is a direct function of the flow rate, increasing the flow rate increases drug release. The use of a small cell resulted in faster drug dissolution and higher Reynold's Number than using a large cell. Tablet position in the cell, also has an effect on drug dissolution, inserting the tablet in a horizontal position inside the cell gave faster dissolution than a vertical position. The hydrodynamic conditions did not affect the drug dissolution from HPMC controlled release tablets indicating that the drug dissolution is controlled by the matrix. An equation to predict drug dissolution from conventional tablets was established: Sh=-21.36+10.58Re(1/2) where R2=0.98. This study demonstrated that hydrodynamic conditions, and type of dissolution testing apparatus used have an effect on dissolution rate, mass transfer rate, and film thickness underlying dissolution process.

Solubility↗

PubMedDate not supplied

[Effect of position with respect to gravitational force on the hydrodynamics of an experimental model of saccular aneurysm].

We wish to confirm the hypothesis that the hydrodynamics of brain aneurysms depend partially on their position, with respect to the force of gravitation, and so developed an experimental model of latex aneurysms, which was subjected to a pulsatile flow. Four different registers were made with an injection of ink and radioisotopes. A physical model was designed which allowed a quantitative analysis of the results and which allows a mathematical analysis of the aneurysm's hydrodynamics. The results suggest that when an aneurysm is oriented against the force of gravity, it has a very low risk of thrombosis, and the scarce turbulence of the flow condition a lower risk of growth and rupture, in comparison with other conditions. The greatest flow turbulence against the wall is found in the aneurysm oriented downwards, that is parallel to the force of gravity. Due to its hydrodynamics, the downwards aneurysm has the highest probability of complication, since it has; a) higher risk of rupture due to the impact of the stream upon the wall and to the turbulence this impact produces, b) a higher risk of thrombosis produced by the circulatory stasis which has a dome. This combination of factors (rupture and thrombosis) allows these aneurysms to grow more than others.

Gravitation↗

PubMed1990

[Urodynamic consequences of urethral stenosis. Hydrodynamic study with a theoretical model].

An urethral model was designed to assess the hydrodynamic consequences of stenosis of the bulbar urethra. This model was based on the geometric and hydrodynamic analysis of micturing urethrograms in a patient whose maximum flow rate was 24 ml/s for a bladder pressure of 40 cm of water. It corresponds to the conditions of flow observed wit maximum bladder pressure and flow rate. During this short period, the shape of the urethra is regarded as stable. Calculation took account of the characteristics of a turbulent flow of urine, of the head loss due to friction of the urine on the walls and of the head loss caused by the geometrical changes of the urethra from the neck of the bladder to the meatus. In these conditions, applying Bernouilli's equation allowed plotting of bladder pressure for various levels of urethral resistance. If there is no stenosis, the theoretical maximum flow rate of the model with a bladder pressure of 40 to 80 cm of water should be 19 to 26 ml/s. Calculation showed that a sudden reduction of the diameter to less than 2.5 mm occurring in a segment of the urethra with a diameter of 4 mm accounts for a flox rate lower than 15 ml/s, except when bladder pressure can exceed 100 cm of water. The decrease in the maximum flow rate caused by urethral stenosis is all the greater as bladder pressure remains low or normal, with other causes of head loss or with associated upstream dilatation. Lastly, progressive narrowing leads to a smaller head loss and will therefore be better tolerated than sudden narrowing to the same caliber. Inversely, a long stenosis will be less well tolerated as the head loss due to friction in a long and narrow passage is increased. The diameter of a stenosis accounting for a maximum flow rate of less than 15 ml/s cannot be determined in the absolute. Analyzing the hydrodynamic consequences of stenosis also requires knowing the associated urodynamic and geometric parameters.

Adult↗

PubMed1989

[The hydrodynamic components in joints: proof of a membrane-cistern system within the calcified zone of the femur head cartilage].

The theoretical postulate of a hydrodynamic system for the transmission of forces at the hip joint led to the discovery of a two-membrane system. Within the calcified cartilaginous zone of the femoral head there exists a system of small spaces and cisterns which can only be understood in the postulated sense as an overall acting hydrodynamic system. A correlation between the destruction of the calcified zone, i.e. the hydrodynamic system, and arthrosis is indicated. Ongoing studies and deliberations will help to discover the true model of the transmission of forces and impulses and to solve the problems of treating arthrosis.

Calcification, Physiologic↗

PubMed1994

Hydrodynamic performance of the Medtronic Freestyle Aortic Root Bioprosthesis.

The Freestyle Aortic Root Bioprosthesis is comprised of a porcine aortic root preserved in buffered 0.2% glutaraldehyde solution. It is fixed at a pressure sufficient to distend the aortic wall, but the leaflets are fixed with no transvalvular gradient. The bioprosthesis is treated with alpha-amino-oleic acid (AOA) to reduce the potential for leaflet calcification. In order to conduct in-vitro performance studies, a simulated aorta test chamber was developed. The test chamber material formulation can be altered to produce a wide range of desired compliances, while maintaining repeatable dimensional specifications. The test chamber design also allows for performance testing simulating a variety of implant techniques. Both Freestyle and the stented control valves (Hancock Standard Model 242) were mounted within the simulated aortas for these studies. Steady state and pulsatile flow pressure drop studies demonstrated a significantly lower gradient across the Freestyle valve when compared to stented Hancock Standard controls. In addition, the smaller size (19,21,23 mm) Freestyle valves had superior EOA's compared to the Standard St. Jude bileaflet mechanical and Hancock modified orifice (MO) porcine valve designs. The regurgitant volumes were equivalent to the control (Hancock Standard model 242) valves when compared to the Freestyle valves with equivalent flow areas. Additional studies were conducted in order to determine the effects of sizing and configuration on hydrodynamic performance. These studies were performed in four configurations: total root, inclusion, partially scalloped (two sinuses) and fully scalloped valve. These studies demonstrated that both pressure drop and regurgitation are significantly affected by valve sizing and implant technique. Accelerated wear studies were performed on three of each size and six of the largest Freestyle valves. Stented Hancock Standard valves and non-AOA treated Freestyle valves were used as controls. Hydrodynamic performance tests were conducted at intervals throughout the study. No evidence was found to indicate a difference in wear or hydrodynamic performance between the AOA treated and untreated Freestyle valves.

Aorta↗

PubMed1994

Hydrodynamic performance of Carbomedics valves in double valve replacement.

Most patients undergoing double valve replacements have reduced myocardial capacity. However, little is known about the influence of valve sizes on myocardial energy consumption in double valve replacement. This study was designed to supply hydrodynamic data for the proper selection of sizes in double valve replacement. A mock loop system was used to measure the energy consumption of CarboMedics valves at conditions resembling rest (5 L/min) and moderate exercise (9 L/min). All combinations of aortic valves size #21 to #27 with mitral prosthesis sizes #25 to #29 were tested separately. Larger size aortic prostheses revealed remarkably less energy consumption up to size #27. Under high flow (9 L/min) this effect was more pronounced. In contrast, mitral valve prosthesis sizes #25 to #29 had similar hydrodynamic data. At low flow conditions (5 L/min) no significant benefit was found with the use of a larger mitral valve. Only a reduction of less than 10 percent of total energy consumption could be achieved with the use of a mitral valve larger than #25 at 9 L/min flow. In conclusion there is no hydrodynamic reason for using a valve larger than #25 in the mitral position for patients who exercise moderately. Continuous reduction of cardiac work can be expected with the use of the largest possible aortic prosthesis up to size #27 at rest and at moderate exercise.

Aortic Valve↗

PubMed1993

Statistics of cell adhesion under hydrodynamic flow: simulation and experiment.

Adhesion under hydrodynamic flow is a step in many complicated physiological processes such as the neutrophil-mediated inflammatory response and cancer cell metastasis. We use a combination of computer simulation and experiment to explore how a population of cells interacts with a ligand-coated substrate under shear flow. To simulate the binding of a single cell to a surface, we use a microvilli-hard sphere model in which receptor-ligand bonds are treated as springs, and the net motion of the cell is determined from a force balance involving hydrodynamic, bonding, and colloidal forces. We show that the adhesive phenotype of a cell depends strongly on the fractional spring slippage of receptor-ligand bonds, which relates the extension of a bond to its rate of breakage; a lower spring slippage indicates bonds can withstand a great deal of extension without a significant increase in the breakage rate, and hence leads to more strongly adherent cells. We construct the behavior of a population of cells by simulating many cells using this algorithm. We show that a homogeneous population of cells with identical numbers of receptors, modeled with parameters suitable to recreate neutrophil rolling, will display a distribution of translational velocities. In addition, we calculate the average velocity for a heterogeneous population of cells which has a Gaussian distribution in receptor number. As the standard deviation of this distribution increases, the average observed velocity for the population increases. Although the homogeneous and heterogeneous populations have the same average number of receptors (10(5)) per cell, there is a significant difference in their average velocity when the standard deviation of receptor number in the heterogeneous population is as little as 25% of the average receptor number. We also present experimental evidence that not all cells exhibit the slow rolling characteristic of neutrophil-endothelial interaction, but rather appear to exist in a "binary" state in which cells are either adherent or noninteracting. We have developed an experimental model system for studying adhesion under hydrodynamic flow, using the rat basophilic leukemia (RBL) derivatized polyacrylamide gels in a flow chamber. Cells are injected into a portion of the flow chamber in which the substrate is not coated with antigen, and allowed to flow over the antigen-coated portion of the gel. We have measured the spatial distribution of cell binding for a population of cells at different flow rates, and have shown that cell binding decreases as shear rate increases.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMedDate not supplied

[Comparative hydrodynamic evaluation of variants of the cavopulmonary anastomosis].

An analysis of the range of postoperative complications following cavapulmonary anastomosis reveals a number of medical engineering problems in surgery techniques. The severity of the surgery due to the nonphysiological rearrangement of blood circulation makes it necessary to search for the most optimal types of anastomosis in terms of the hemo- and hydrodynamics of circulation. To optimize the performance of cavapulmonary anastomosis, namely to define the mutual localization and orientation of the implanted anastomoses against the axes of inflow and outflow, hemo- and hydrodynamic studies were made by Doppler laser anemometry. From the hydrodynamic point of view, the findings indicate the most optimal type of cavapulmonary anastomosis-cruciform anastomosis by displacing 0.5 d from the outflow axis at an angle of 60ë5 degrees.

Anastomosis, Surgical↗

PubMed1998

[Rheological and hydrodynamic properties of blood from patients with stable angina pectoris: correction with high molecular polyethylene oxide].

Rheological and hydrodynamic properties of blood taken from patients with stable angina pectoris were investigated in different periods (1, 7 and 28 days) of combined treatment (calcium antagonists, nitrates, beta-blockers, aspirin). The high viscosity syndrome (elevated blood viscosity, red cell aggregation, hyperfibrinogenemia) was registered before treatment, 1, 7 and 28 days after beginning of the treatment. Low hydrodynamic index (the speed of blood flow in turbulent regimen) reflected insufficiency of endogenic antiturbulent factor in the blood. The addition of high-molecular-weight polyethylene oxide to blood samples in concentration 2 x 10(-6) promoted normalization of the hydrodynamic index and decline of red cell hyperaggregation.

Adult↗

PubMed1960

Experimental study of the independence of diffusion and hydrodynamic permeability coefficients in collodion membranes.

The two parameters usually invoked when discussing transport across membranes are the "diffusion permeability coefficient" and the "hydrodynamic permeability coefficient." In this study the magnitude of these two coefficients is established experimentally for collodion membranes of differing porosities. The hydrodynamic permeability is predominant while convergence of the two permeabilities tends to obtain as the membranes become less coarse. The flux data obtained are used to calculate "average pore diameter" and the meaningfulness of these calculations is interpreted. The relationship between the two coefficients and transport across membranes as treated by the system of irreversible thermodynamics is discussed.

Biological Transport↗

PubMed1961

Determination of the effective hydrodynamic radii of small molecules by viscometry.

The effective hydrodynamic radii of small uncharged molecules in dilute aqueous solution were determined using Einstein's classical theory of viscosity. The radii thus obtained are those of a hypothetical sphere whose hydrodynamic behavior is the same as that of the solute molecule plus that water of hydration which is too firmly bound to partake in the viscous shearing process. The results obtained compare favorably with radii determined from molecular models constructed in accordance with atomic dimensions compiled by Pauling. Although the application of the Einstein theory to molecules whose size is comparable to that of water represents a considerable extrapolation, the results suggest that this deviation from the assumptions of the theory, in the case of the molecules studied, is of second order importance. Employing the viscometric radii, we have formulated an empirical correction of the Stokes-Einstein diffusion equation. This correction is similar in form to those previously proposed by Cunningham (22) and Millikan (21) and is of particular significance when the solute molecule is comparable in size to the discontinuities of the surrounding medium. The molecular radii of a number of small organic molecules obtained by means of the corrected Stokes-Einstein equation do not differ significantly from the radii obtained from molecular models of these compounds.

Diffusion↗

PubMed1998

Influence of hydrodynamic conditions on naphthalene dissolution and subsequent biodegradation.

The influence of hydrodynamic conditions on the dissolution rate of crystalline naphthalene as a model polycyclic aromatic hydrocarbon (PAH) was studied in stirred batch reactors with varying impeller speeds. Mass transfer from naphthalene melts of different surface areas to the aqueous phase was measured and results were modeled according to the film theory. Results were generalized using dimensionless numbers (Reynolds, Schmidt, and Sherwood). In combined mass transfer and biodegradation experiments, the effect of hydrodynamic conditions on the degradation rate of naphthalene by Pseudomonas 8909N was studied. Experimental results were mathematically described using mass-transfer and microbiological models. The experiments allowed determination of mass-transfer and microbiological parameters separately in a single run. The biomass formation rate under mass transfer limited conditions, which is related to the naphthalene biodegradation rate, was correlated to the dimensionless Reynolds number, indicating increased bioavailability at increased mixing in the reactor liquid. The methodology presented in which mass transfer processes are quantified under sterile conditions followed by a biodegradation experiment can also be adapted to more complex and realistic systems, such as particulate, suspended PAH solids or soils with intrapartically sorbed contaminants when the appropriate mass-transfer equations are incorporated.

Biodegradation, Environmental↗

PubMed2000

The role of Joule heating in dispersive mixing effects in electrophoretic cells: hydrodynamic considerations.

The analysis described in this contribution is focused on the effect of Joule heating generation on the hydrodynamics of batch electrophoretic cells (i.e., cells that do not display a forced convective term in the motion equation). The hydrodynamics of these cells is controlled by the viscous forces and by the buoyancy force caused by the temperature gradients due to the Joule heating generation. The analysis is based on differential models that lead to analytical and/or asymptotic solutions for the temperature and velocity profiles of the cell. The results are useful in determining the characteristics of the temperature and velocity profiles inside the cell. Furthermore, the results are excellent tools to be used in the analysis of the dispersive-mixing of solute when Joule heating generation must be accounted for. The analysis is performed by identifying two sequentially coupled problems. Thus, the "carrier fluid problem" and the "solute problem" are outlined. The former is associated with all the factors affecting the velocity profile and the latter is related to the convective-diffusion aspects that control the spreading of the solute inside the cell. The analysis of this contribution is centered on the discussion of the "carrier fluid problem" only. For the boundary conditions selected in the contribution, the study leads to the derivation of an analytical temperature and a "universal" velocity profile that feature the Joule heating number. The Grashof number is a scaling factor of the actual velocity profile. Several characteristics of these profiles are studied and some numerical illustrations have been included.

Electric Impedance↗