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Results for “Experimental validation”

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At least 919 records · Page 51Linked to original sources

PubMed1993

Accuracy of right ventricular output estimated by Doppler echocardiography in the sheep fetus.

OBJECTIVE: Our goal was to determine whether Doppler ultrasonographic estimation of fetal right ventricular output was accurate enough to evaluate fetal cardiac performance before the technique can be applied with confidence to the human fetus. The accuracy of this method has not been validated experimentally. STUDY DESIGN: We compared the right ventricular output measured by Doppler echocardiography with that determined from a transit-time ultrasonic flowmeter placed around the fetal pulmonary trunk and to that determined by microsphere technique. We obtained 72 Doppler flow measurements and 16 microsphere flow measurements in six fetuses. RESULTS: There was a fair correlation between cardiac output estimated by Doppler echocardiography performed transabdominally and that determined by a transit-time flowmeter (r = 0.76). The correlation was excellent when Doppler echocardiography was performed by the trans-uterine approach (r = 0.94). There was also an excellent correlation between right ventricular output determined by a transit-time flowmeter and that by microsphere technique (r = 0.94). CONCLUSION: Doppler echocardiographic estimation of fetal right ventricular cardiac output is thus feasible and accurate.

Animals↗

PubMed2000

The effect of bone morphogenetic protein-7 on the expression of type I inositol 1,4,5-trisphosphate receptor in G-292 osteosarcoma cells and primary osteoblast cultures.

Bone morphogenetic protein-7 (BMP-7) affects differentiation of preosteoblasts enabling the resultant cells to respond optimally to acutely acting regulators. As the phosphoinositide cascade and, particularly, the calcium-mobilizing inositol 1,4,5-trisphosphate (InsP3) receptor are integral to stimulus-secretion coupling in osteoblasts, the hypothesis that BMP-7 affects InsP3 receptor expression was examined in the G-292 human osteosarcoma cell line and in primary cultures of human osteoblasts. G-292 osteosarcoma cells were found to be a valid experimental model for primary human osteoblasts, expressing osteoblastic mRNAs encoding osteocalcin, bone sialoprotein, alkaline phosphatase, alpha1-collagen, epidermal growth-factor receptor, and BMP type II receptor. When cultured long term in the presence of ascorbic acid and beta-glycerophosphate, G-292 cells underwent further osteoblastic differentiation, forming nodules and exhibiting restricted mineralization. G-292 cells responded to BMP-7 with an increase in InsP3 receptor density. Ligand-binding studies established that BMP-7 (50 ng/ml) treatment of G-292 cells increased InsP3 receptor density 2.4-fold with no apparent change in affinity. Immunoblot analysis with antibodies specific for type I, type II, and type III InsP3 receptors revealed that BMP-7 (50 ng/ml) treatment resulted in a specific increase (206+/-8%) in the type I receptor. Reverse transcription-polymerase chain reaction and Northern blot analyses of G-292 and primary human osteoblasts confirmed an increase in type I InsP3 receptor mRNA upon BMP-7 treatment. These results demonstrate that G-292 cells respond to BMP-7 with an increase InsP3 receptor density, consistent with the enhanced capacity of these cells to respond to Ca2+-mobilizing secretory hormones during osteoblast differentiation.

Alkaline Phosphatase↗

PubMed2000

Evaluation of the number of agonist molecules needed to activate a ligand-gated channel from the current rising phase.

We propose a new method for calculating the number of agonist binding sites (n) in ligand-gated receptor channels from the initial phase of the current. This method is based on the fact that the relation between the current (I) and its first-time derivative (I') at the beginning of the current reflects the number of transitions that lead to channel opening. We show that, for constant agonist concentration, the above relationship at t --> 0 provides the number of steps leading to channel opening. When the agonist concentration is not constant but rather increases linearly with time, the corresponding value can be obtained using a slightly modified procedure. The analytical results were compared with computer simulations and a good match between the two was obtained. The theoretical procedure was then validated experimentally using the nicotinic receptor, because, for this receptor, the number of binding sites is well established. Indeed, the expected number of two binding sites was obtained. The method was then tested for the quisqualate-type glutamate receptor channel from the opener muscle of crayfish. The number of this receptor's binding sites is not fully resolved. Our results suggest that, for this glutamate receptor as well, two binding sites must be occupied to open the channel.

Animals↗

PubMed1990

Receptor-mediated adhesion phenomena. Model studies with the Radical-Flow Detachment Assay.

Receptor-mediated cell adhesion phenomena play a vital role in many physiological and biotechnology-related processes. To investigate the physical and chemical factors that influence the cell/surface interaction, we have used a radial flow device, a so-called Radial-Flow Detachment Assay (RFDA). The RFDA allows us to make direct observations of the detachment process under specified experimental conditions. In results reported here, we have studied the detachment of receptor-coated latex beads (prototype cells) from ligand-coated glass surfaces. The receptors and ligands used in this work are complementary antibodies. The beads enable us to examine several aspects of the adhesion process with particles having uniform properties that can be varied systematically. Advantages of the RFDA are many, especially direct observation of cell detachment over a range of shear stresses with quantitative measurement of the adhesive force. We focus our studies on the effects of ligand and receptor densities, along with the influence of pH and ionic strength of the medium. These data are analyzed with a mathematical model based on the theoretical framework of Bell, G. I. (1978. Science [Wash. DC]. 200:618-627) and Hammer, D. A. and D. A. Lauffenburger (1987. Biophys. J. 52:475-487). We demonstrate experimental validation of a theoretical expression for the critical shear stress for particle detachment, and show that it is consistent with reasonable estimates for the receptor-ligand bond affinity.

Antibodies↗

PubMed1996

Cytoplasmic viscosity near the cell plasma membrane: translational diffusion of a small fluorescent solute measured by total internal reflection-fluorescence photobleaching recovery.

Total internal reflection-fluorescence recovery after photobleaching (TIR-FRAP) was applied to measure solute translational diffusion in the aqueous phase of membrane-adjacent cytoplasm. TIR fluorescence excitation in aqueous solutions and fluorescently labeled cells was produced by laser illumination at a subcritical angle utilizing a quartz prism; microsecond-resolution FRAP was accomplished by acousto-optic modulators and electronic photomultiplier gating. A mathematical model was developed to determine solute diffusion coefficient from the time course of photobleaching recovery, bleach time, bleach intensity, and evanescent field penetration depth; the model included irreversible and reversible photobleaching processes, with triplet state diffusion. The validity and accuracy of TIR-FRAP measurements were first examined in aqueous fluorophore solutions. Diffusion coefficients for fluorescein isothiocyanate-dextrans (10-2000 kDa) determined by TIR-FRAP (recovery t1/2 0.5-2.2 ms) agreed with values measured by conventional spot photobleaching. Model predictions for the dependence of recovery curve shape on solution viscosity, bleach time, and bleach depth were validated experimentally using aqueous fluorescein solutions. To study solute diffusion in cytosol, MDCK epithelial cells were fluorescently labeled with the small solute 2',7'-bis-2-carboxyethyl-5-carboxyfluorescein-acetoxymethyl-ester (BCECF). A reversible photobleaching process (t1/2 approximately 0.5 ms) was identified that involved triplet-state relaxation and could be eliminated by triplet-state quenching with 100% oxygen. TIR-FRAP t1/2 values for irreversible BCECF bleaching, representing BCECF translational diffusion in the evanescent field, were in the range 2.2-4.8 ms (0.2-1 ms bleach times), yielding a BCECF diffusion coefficient 6-10-fold less than that in water. These results establish the theory and the first experimental application of TIR-FRAP to measure aqueous-phase solute diffusion, and indicate slowed translational diffusion of a small solute in membrane-adjacent cytosol.

Animals↗

PubMed1997

Optimal techniques for arterial gene transfer.

Cardiovascular gene therapy is becoming a clinical reality due to improved vectors, delivery systems and careful experimental validation studies. Nearly all cardiovascular diseases are amenable to gene therapy, but the optimal combination of vector, delivery system and therapeutic gene is likely to be unique to each application. Currently, the most efficient vectors available are replication-defective adenoviral vectors, but transgene expression is limited in time due to a strong immune response. Conversely, non-viral vectors or plasmid DNA may be used safely but have very limited efficiency. Percutaneous, catheter-based delivery is feasible for most applications. The ultimate issues that will decide of the future of gene therapy are safety of the transfer and delivery techniques as well as cost/effectiveness comparisons with alternative therapies, including local delivery of drugs, proteins and/or mechanical devices.

Arteries↗

PubMed2006

Identification of statistical patterns in complex systems via symbolic time series analysis.

Identification of statistical patterns from observed time series of spatially distributed sensor data is critical for performance monitoring and decision making in human-engineered complex systems, such as electric power generation, petrochemical, and networked transportation. This paper presents an information-theoretic approach to identification of statistical patterns in such systems, where the main objective is to enhance structural integrity and operation reliability. The core concept of pattern identification is built upon the principles of Symbolic Dynamics, Automata Theory, and Information Theory. To this end, a symbolic time series analysis method has been formulated and experimentally validated on a special-purpose test apparatus that is designed for data acquisition and real-time analysis of fatigue damage in polycrystalline alloys.

Artificial Intelligence↗

PubMed2000

The mesh-matching algorithm: an automatic 3D mesh generator for finite element structures.

Several authors have employed finite element analysis for stress and strain analysis in orthopaedic biomechanics. Unfortunately, the definition of three-dimensional models is time consuming (mainly because of the manual 3D meshing process) and consequently the number of analyses to be performed is limited. The authors have investigated a new patient-specific method allowing automatically 3D mesh generation for structures as complex as bone for example. This method, called the mesh-matching (M-M) algorithm, generated automatically customized 3D meshes of anatomical structures from an already existing model. The M-M algorithm has been used to generate FE models of 10 proximal human femora from an initial one which had been experimentally validated. The automatically generated meshes seemed to demonstrate satisfying results.

Algorithms↗

PubMed2000

A two-dimensional fluid-structure interaction model of the aortic valve [correction of value].

Failure of synthetic heart valves is usually caused by tearing and calcification of the leaflets. Leaflet fiber-reinforcement increases the durability of these valves by unloading the delicate parts of the leaflets, maintaining their physiological functioning. The interaction of the valve with the surrounding fluid is essential when analyzing its functioning. However, the large differences in material properties of fluid and structure and the finite motion of the leaflets complicate blood-valve interaction modeling. This has, so far, obstructed numerical analyses of valves operating under physiological conditions. A two-dimensional fluid-structure interaction model is presented, which allows the Reynolds number to be within the physiological range, using a fictitious domain method based on Lagrange multipliers to couple the two phases. The extension to the three-dimensional case is straightforward. The model has been validated experimentally using laser Doppler anemometry for measuring the fluid flow and digitized high-speed video recordings to visualize the leaflet motion in corresponding geometries. Results show that both the fluid and leaflet behaviour are well predicted for different leaflet thicknesses.

Aortic Valve↗

PubMed2003

Hill muscle model errors during movement are greatest within the physiologically relevant range of motor unit firing rates.

This study evaluated the accuracy of Hill-type muscle models during movement. Hill-type models are ubiquitous in biomechanical simulations. They are attractive because of their computational simplicity and close relation to commonly measured experimental variables, but there have been surprisingly few experimental validations of these models during functionally relevant conditions. Our hypothesis was that model errors during movement are largest at the low motor unit firing rates most relevant to normal movement conditions. This hypothesis was evaluated in the cat soleus muscle activated either by electrical stimulation at physiological rates or via the crossed-extension reflex (CXR) thereby obtaining normal patterns of motor unit recruitment and rate modulation. These activation paradigms were applied during continuous movements approximately matched to locomotor length changes. The resulting muscle force was modeled using a common Hill model incorporating independent activation, tetanic length-tension and tetanic force-velocity properties. Errors for this model were greatest for stimulation rates between approximately 10-20Hz. Errors were especially large for muscles activated via the CXR, where most motor units appear to fire within this range. For large muscle excursions, such as those seen during normal locomotion, the errors for naturally activated muscle typically exceeded 50%, supporting our hypothesis and indicating that the Hill model is not appropriate for these conditions. Subsequent analysis suggested that model errors were due to the common Hill model's inability to account for the coupling between muscle activation and force-velocity properties that is most prevalent at the low motor unit firing rates relevant to normal activation.

Animals↗

PubMed2002

Optimal design of batch and simulated moving bed chromatographic separation processes.

Preparative chromatography, especially simulated moving bed (SMB) chromatography, is a key technology for the separation of fine chemicals on a production scale. Most of the design methods for batch and SMB processes proposed in the open literature deal with the optimisation of the operating conditions for a given chromatographic unit only. Therefore, a comparison of the process economy may lead to incorrect results. In this contribution, an effective strategy for the optimal choice of all process parameters (operation and design parameters) is proposed. The main idea of this strategy is to apply a detailed and experimentally validated process model and to reduce the number of influencing parameters by introducing and optimising dimensionless process parameters. It is shown that there is an infinite choice of design and operating parameters to achieve maximum productivity or minimum separation costs and not at the maximum pressure drop only. The detailed design of the chromatographic unit and the selection of the operating conditions can be adjusted by considering the availability of columns and packing materials. As the model system, the separation of a racemic mixture (EMD53986) on Chiralpak AD was investigated. After complete optimisation of a batch and a SMB unit, a real comparison of the process economy can be achieved. Finally, the influences of two different objective functions, productivity and specific separation cost, are analysed.

Chromatography, Liquid↗

PubMed2003

General theory for flow optimisation of split-flow thin fractionation.

Recently, magnetic split-flow thin (SPLITT) fractionation has been developed to separate macromolecules, colloids, cells and particles. However, the previous theory, developed for an infinitely long channel, needs to be improved to consider the flow transit regimes at both inlet and outlet. In this paper, we describe a new approach to optimising flow-rates for particle separation which considers the effect of flow transit region. Surprisingly, the critical particle migration velocities derived by the present theory are identical to the previous simplified theory. Therefore, the previous simplified theory may have wider application than might have been expected. As a test of our theory, a numerical simulation based on solving Navier-Stokes equations has also been carried out for a magnetic SPLITT device. The trajectory of a particle with the critical migration velocity is exactly as expected by our theory. Following experimental validation, this work will facilitate the design of new SPLITT fractionation systems with smaller aspect ratio.

Chemical Fractionation↗

PubMed1999

Chemometric approach to the treatment of benzodiazepine separation and peak broadening in capillary electrophoresis.

A chemometric methodology was used to study capillary efficiency and the separation of ten benzodiazepines in capillary electrophoresis. The resolution between two adjacent peaks on the electropherogram was estimated and the overall quality of the separation was assessed by means of a new response function. The nature (methanol or acetonitrile) and proportion of the organic modifier both in the background electrolyte and the sample buffer and the injection time were considered. The results predicted that if the sample had a lower dielectric constant than the background electrolyte buffer then a much larger injection volume could be used. The computer optimization routine was experimentally validated and the result demonstrated that the fastest electrophoretic reparation was obtained with acetonitrile (7 min instead of 9 min with methanol).

Acetonitriles↗

PubMed2003

Structural characterisation and functional significance of transient protein-protein interactions.

Protein-protein complexes that dissociate and associate readily, often depending on the physiological condition or environment, play an important role in many biological processes. In order to characterise these "transient" protein-protein interactions, two sets of complexes were collected and analysed. The first set consists of 16 experimentally validated "weak" transient homodimers, which are known to exist as monomers and dimers at physiological concentration, with dissociation constants in the micromolar range. A set of 23 functionally validated transient (i.e. intracellular signalling) heterodimers comprise the second set. This set includes complexes that are more stable, with nanomolar binding affinities, and require a molecular trigger to form and break the interaction. In comparison to more stable homodimeric complexes, the weak homodimers demonstrate smaller contact areas between protomers and the interfaces are more planar and polar on average. The physicochemical and geometrical properties of these weak homodimers more closely resemble those of non-obligate hetero-oligomeric complexes, whose components can exist either as monomers or as complexes in vivo. In contrast to the weak transient dimers, "strong" transient dimers often undergo large conformational changes upon association/dissociation and are characterised with larger, less planar and sometimes more hydrophobic interfaces. From sequence alignments we find that the interface residues of the weak transient homodimers are generally more conserved than surface residues, consistent with being constrained to maintain the protein-protein interaction during evolution. Protein families that include members with different oligomeric states or structures are identified, and found to exhibit a lower sequence conservation at the interface. The results are discussed in terms of the physiological function and evolution of protein-protein interactions.

Animals↗

PubMed1988

Bone resorption induced by transplanted bladder tumor (MBT-2) in mice.

The high incidence of metastatic bone resorption in urological cancer makes it necessary for clinicians to look for a valid experimental model to investigate basic interaction between cancer cells and bone in order to improve the treatment. A new model of bone resorption has been defined, namely the subcutaneous injection of tumor cell suspensions of invasive transitional cell carcinoma of the bladder (MBT-2) into mice after the periosteum of the calvaria has been disrupted. The tumor induced osteolysis associated with osteoclast proliferation with reactive bone formation. Moreover, we were able to show hypercalcemia accompanied with local bone resorption in this model.

Animals↗

PubMed1998

Mathematical determination of feeding patterns and its consequence on correlational studies.

The literature contains discrepancies on the definition of parameters of feeding pattern and, consequently, on the relation between the size of a meal and the interval that precedes and follows it. In this paper, based on 1513 meals recorded on 22 rats, we used a modified method to set up the parameters of ingestive behavior based on one main principle: no parameter had to be pre-defined before the raw data were processed. Then, the characteristics of the meal, meal duration, meal size, intra-meal pauses, inter-meal intervals, and rate of ingestion were determined. Once the characteristics of the meal were set up, our method was experimentally validated by offering scheduled meals. Depending on the ingestion rate, three classes of meals were also identified: slow-, medium-, and fast-rate meals. i.e., there were individuals who tended to eat slowly while others ate faster. Besides validating the proposed method, the collected data were also used to revisit the question concerning the post-prandial correlations. The correlations between meal size and the pre or post-prandial intervals weren't confirmed. However, when we applied to our own data previous methods of analysis based on arbitrary criteria used by other authors, we verified those correlations. By reinforcing the principle of using raw data and objective criteria to define feeding behavior parameters, this study allows to further consider the meal-to-meal relations and raises the problem of the interpretation of such relations in terms of their physiological significance.

Animals↗

PubMed2002

Laser-based ultrasonic inspection with a fiber-coupled scanning Cassegrain system.

State-of-the-art integrally stiffened composite materials, manufactured for use in the next generation of commercial and military aircraft, are increasingly being used for structural components such as wings and fuselages. However, the complexity of the manufacturing processes can produce small variations in the shape of integrally stiffened composite structures. Thus, a priori knowledge of the nominal part shape often does not provide sufficient accuracy to allow an automated conventional ultrasonic inspection. In contrast, automated inspections of integrally stiffened structures can be performed using laser-based ultrasound techniques since a priori knowledge of the nominal part shape is adequate to scan the laser beams over the structure. This paper addresses the issues associated with the extension of laser-based ultrasonics to inspections in remote and limited access areas, and describes the implementation of a fiber-based remote and limited access LBU inspection system based upon a Cassegrain scanning and optical collection system. The ability to quickly and directly manipulate flexible low mass optical fibers equipped with specialized endoscopic scanning optics make fiber systems an attractive method for the development of limited and remote access inspection systems. The Cassegrain optical system is described in detail and both numerical and experimental validation of the system operational characteristics are presented.

Journal Article↗

PubMed2002

Diagnostic ultrasound artifacts during imaging of two-body interfaces: part 1--wavelength resonance.

A diagnostic ultrasound technique is to be developed for measuring surface contact areas at the tibio-femoral interface of a total knee replacement in an in vitro industrial engineering setting as a design tool. As a first step, a previous study mathematically characterized the ultrasound behaviour expected at a two-body circular-on-flat interface of known geometry. In the current investigation, a series of test objects was constructed and imaged to experimentally validate the theoretical contact models. Specifically, several unique metal-on-polymer test objects, whose interfaces were point, non-point, and circular contact areas, were ultrasonically imaged. The effects of interface geometry, ultrasound resonance wavelength, lambda/2, and compressive load were studied.

Aluminum↗