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  • Articles  (11)
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  • Springer  (11)
  • Blackwell Publishing Ltd
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  • 1995-1999  (11)
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  • 1970-1974
  • 1965-1969
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  • Technology  (10)
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    A method for assessing geometrical errors in layered manufacturing. Part 2: Mathematical modelling and numerical evaluation (1998)
    Springer
    The international journal of advanced manufacturing technology 14 (1998), S. 644-650 
    Details
    ISSN: 1433-3015
    Keywords: Error interaction ; Error transfer ; Geometrical error ; Layered manufacturing ; Mathematical model ; Rapid prototyping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Layered manufacturing based rapid prototyping processes are subjected to not only a staircase effect owing to the approximating process used, but also an accumulated error transfer between layers. Certain types of error such as surface tilting and layer thickness variations that occur in one layer can transfer to other layers above it. This paper describes a mathematical model based on the physical and geometrical models discussed in Part 1 of the paper. The model uses the matrix transformation method to analyse the effect of transformation of local errors to the multiple layer global errors. A data preparation error transformation matrix is used to describe the error interactions between layers during the data preparation stage. A disturbance error transformation matrix is used to describe the error interaction within each layer and error propagation between layers during the part building process. This model describes geometrical error analysis involving profiling error, layer inclination and layer thickness variations. Numerical evaluation of the model is carried out for a typical benchmark component.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01192284
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  • 2
    Electronic Resource
    Electronic Resource
    A Mathematical Model of Gas Exchange in an Intravenous Membrane Oxygenator (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 166-178 
    Details
    ISSN: 1573-9686
    Keywords: ARDS ; Intravenous oxygenation ; Artificial lung ; Mathematical model ; Model ; Gas exchange ; Oxygenator
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Acute respiratory distress syndrome (ARDS) is a pulmonary edemic condition which reduces respiratory exchange in 150,000 people per year in the United States. The currently available therapies of mechanical ventilation and extracorporeal membrane oxygenation are associated with high mortality rates, so intravenous oxygenation represents an attractive, alternative support modality. We are developing an intravenous membrane oxygenator (IMO) device intended to provide 50% of basal oxygen and carbon dioxide exchange requirements for ARDS patients. A unique aspect of the IMO is its use of an integral balloon to provide active mixing. This paper describes a mathematical model which was developed to quantify and optimize the gas exchange performance of the IMO. The model focuses on balloon activated mixing, uses a lumped compartment approach, and approximates the blood-side mass transfer coefficients with cross-flow correlations. IMO gas exchange was simulated in water and blood, for a variety of device geometries and balloon pulsation rates. The modeling predicts the following: (1) gas exchange efficiency is reduced by a buildup of oxygen in the fluid near the fibers; (2) the IMO gas exchange rate in blood is normally about twice that in water under comparable conditions; (3) a balloon diameter of about 1.5 cm leads to optimal gas exchange performance; and (4) in vivo positioning can affect gas exchange rates. The numerically predicted gas transfer rates correlate closely with those experimentally measured in vitro for current IMO prototypes. © 1998 Biomedical Engineering Society. PAC98: 8710+e, 8790+y, 8265Fr
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.53
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  • 3
    Electronic Resource
    Electronic Resource
    An Analysis of Hypoxia in Sheep Brain using a Mathematical Model (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 48-59 
    Details
    ISSN: 1573-9686
    Keywords: Oxygen transport ; Microcirculation ; Cerebral circulation ; Hypoxia ; Carbon monoxide ; Mathematical model ; Computer simulation ; Anemia ; Hematocrit ; Brain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Cerebral blood flow (CBF) increases as arterial oxygen content falls with hypoxic (low PO2), anemic (low hemoglobin) and carbon monoxide (CO) (high carboxyhemoglobin) hypoxia. Despite a higher arterial PO2, CO hypoxia provokes a greater increase in CBF than hypoxic hypoxia. We analyzed published data using a compartmental mathematical model to test the hypothesis that differences in PO2 in tissue, or a closely related vascular compartment, account for the greater response to CO hypoxia. Calculations showed that tissue, but not arteriolar, PO2 was lower in CO hypoxia because of the increased oxyhemoglobin affinity with CO hypoxia. Analysis of studies in which oxyhemoglobin affinity was changed independently of CO supports the conclusion that changes in tissue PO2 (or closely related capillary or venular PO2) are predictive of alterations in CBF. We then sought to determine the role of tissue PO2 in anemic hypoxia, with no change in arterial and little, if any, change in venous PO2. Calculations predict a small fall in tissue PO2 as hematocrit decreases from 55% to 20%. However, calculations show that changes in blood viscosity can account for the increase in CBF in anemic hypoxia over this range of hematocrits. © 1998 Biomedical Engineering Society. PAC98: 8710+e, 8722-q, 8745Ft
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.50
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  • 4
    Electronic Resource
    Electronic Resource
    Estimation of Blood Flow Heterogeneity in Human Skeletal Muscle Using Intravascular Tracer Data: Importance for Modeling Transcapillary Exchange (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 764-774 
    Details
    ISSN: 1573-9686
    Keywords: Mathematical model ; Parameter estimation ; Flow heterogeneity ; Skeletal muscle ; Glucose ; Blood flow heterogeneity ; Modeling transcapillary exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Distributed models of blood-tissue exchange are widely used to measure kinetic events of various solutes from multiple tracer dilution experiments. Their use requires, however, a careful description of blood flow heterogeneity along the capillary bed. Since they have mostly been applied in animal studies, direct measurement of the heterogeneity distribution was possible, e.g., with the invasive microsphere method. Here we apply distributed modeling to a dual tracer experiment in humans, performed using an intravascular (indocyanine green dye, subject to distribution along the vascular tree and confined to the capillary bed) and an extracellular ([3H]-D-mannitol, tracing passive transcapillary transfer across the capillary membrane in the interstitial fluid) tracer. The goal is to measure relevant parameters of transcapillary exchange in human skeletal muscle. We show that assuming an accurate description of blood flow heterogeneity is crucial for modeling, and in particular that assuming for skeletal muscle the well-studied cardiac muscle blood flow heterogeneity is inappropriate. The same reason prevents the use of the common method of estimating the input function of the distributed model via deconvolution, which assumes a known blood flow heterogeneity, either defined from literature or measured, when possible. We present a novel approach for the estimation of blood flow heterogeneity in each individual from the intravascular tracer data. When this newly estimated blood flow heterogeneity is used, a more satisfactory model fit is obtained and it is possible to reliably measure parameters of capillary membrane permeability-surface product and interstitial fluid volume describing transcapillary transfer in vivo. © 1998 Biomedical Engineering Society. PAC98: 8745Ft, 8710+e, 8722Fy
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.64
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  • 5
    Electronic Resource
    Electronic Resource
    Design of a Novel Apparatus to Study Nitric Oxide (NO) Inhibition of Platelet Adhesion (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 1036-1043 
    Details
    ISSN: 1573-9686
    Keywords: Mathematical model ; Perfusion ; Diffusion ; Collagen ; Nitric oxide (NO) inhibition ; Platelet adhesion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Nitric oxide (NO) is a simple biological molecule which inhibits adhesion and aggregation of platelets. A novel NO delivery device has been developed to quantitatively study the effects of NO concentration and flux on the adhesion of platelets to a surface. The slit-flow device is lined with a protein-coated membrane through which NO gas permeates into a perfusing platelet suspension. A model predicting spatial NO concentrations and fluxes within the flow slit was validated. At a wall shear rate of 250s-1, platelet adhesion was inhibited 87% relative to controls for exposures as low as 0.1 ppm NO. Corresponding model predictions of the aqueous NO concentration and fluxes at the surface were 0.15 nM, and between 0.5 and 1.1 nanomoles cm-2 s-1, respectively. Endo-thelial cells, which release NO to inhibit platelet adhesion in vivo, generate NO at an estimated flux similar to the above values. At a NO exposure of 0.02 ppm, platelet inhibition was only 10%. The delivery device is useful for other studies in which a knowledge of the spatial NO fluxes or concentrations is desired. Knowledge of these fluxes or concentrations is beneficial towards the design of biomaterials incorporating NO to inhibit platelet adhesion. © 1998 Biomedical Engineering Society. PAC98: 8745Hw, 8722Fy, 8780+s, 8710+e, 8380Lz
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.34
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  • 6
    Electronic Resource
    Electronic Resource
    Enhancement of O2 and CO2 Transfer Through Microporous Hollow Fibers by Pressure Cycling (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 1044-1054 
    Details
    ISSN: 1573-9686
    Keywords: Lung ; Gas exchange ; Mathematical model ; O2 and CO2 transfer ; Microporous hollow fibers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract An intravascular gas exchange device for the treatment of respiratory failure consisted of a multitude of blind-ended hollow fibers glued in a pine-needle arrangement to a central gas supply catheter. It has previously been shown that gas desorption rates can be significantly enhanced by cycling gas pressure between a hypobaric level of 130 and an ambient level of 775 Torr. In this study, influences of the cycling frequency (f) and the cycle fraction during which hypobaric pressure is applied (Θ) were investigated. Rates of O2 desorption from O2-saturated water and CO2 desorption from CO2-saturated water into a manifold containing 198 fibers, 380 μm in diameter, were measured over a range of f from 0.2 to 1.0 Hz, Θ from 0.1 to 0.8, and fiber lengths from 4 to 16 cm. Relative to operation at ambient pressure, pressure cycling increased O2 transfer 3–4 times and CO2 transfer 4–6 times when the water flowed over the fiber manifold at 2.3 l/min. Transfer rates were relatively insensitive to f and Θ with 80–90% of maximum enhancement obtained when Θ was as low as 0.2. Transfer rates increased continuously with fiber length, implying that pressure cycling reduced the intra-fiber resistance to gas diffusion. A mathematical diffusion model which utilized only two adjustable parameters, a mass transfer coefficient for O2 and for CO2, simulated the trends exhibited by desorption data. © 1998 Biomedical Engineering Society. PAC98: 8745Hw, 8790+y
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.115
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  • 7
    Electronic Resource
    Electronic Resource
    The Microcirculation Physiome Project (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 911-913 
    Details
    ISSN: 1573-9686
    Keywords: Physiological database ; Mathematical model ; Physiome: microcirculation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Presented is a discussion of steps towards the creation of a database of the microcirculation encompassing anatomical and functional experimental data, and conceptual and computational models. The discussion includes issues of database utility, organization, data deposition, and linkage to other databases. The database will span levels from gene to tissue and will serve both research and educational purposes. © 1998 Biomedical Engineering Society. PAC98: 8745Ft, 8710+e, 0130Cc
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.112
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  • 8
    Electronic Resource
    Electronic Resource
    Accounting for the Heterogeneity of Capillary Transit Times in Modeling Multiple Indicator Dilution Data (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 914-930 
    Details
    ISSN: 1573-9686
    Keywords: Flow distribution ; Axial diffusion ; Mathematical model ; Perfusion heterogeneity ; Relative dispersion ; Heterogeneity ; Capillary transit times ; Indicator dilution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract To mathematically model multiple indicator dilution (MID) data for the purpose of estimating parameters descriptive of indicator-tissue interactions, it is necessary to account for the effects of the distribution of capillary transit times, hc(t) In this paper, we present an efficient approach for incorporating hc(t) in the mathematical modeling of MID data. In this method, the solution of the model partial differential equations obtained at different locations along the model capillary having the longest transit time provides the outflow concentrations for all capillaries. When weighted by hc(t) these capillary outflow concentrations provide the outflow concentration versus time curve for the capillary bed. The method is appropriate whether the available data on capillary dispersion are in terms of capillary transit time or relative flow distributions, and whether the dispersion results from convection time differences among heterogeneous parallel pathways or axial diffusion along individual pathways. Finally, we show that the knowledge of a relationship among the moments of hc(t) rather than hc(t) per se, is sufficient information to account for the effect of hc(t) in the mathematical modeling interpretation of MID data. This relationship can be determined by including a flow-limited indicator in the injected bolus, thus providing an efficient means for obtaining the experimental data sufficient to account for capillary flow and transit time heterogeneity in MID modeling. © 1998 Biomedical Engineering Society. PAC98: 8745Ft, 8710+e, 0230Jr
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.138
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  • 9
    Electronic Resource
    Electronic Resource
    A Computational Analysis of FXa Generation by TF:FVIIa on the Surface of Rat Vascular Smooth Muscle Cells (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 28-36 
    Details
    ISSN: 1573-9686
    Keywords: Mathematical model ; Tissue factor ; Wall shear rate ; FXa generation ; TF:FVIIa ; Rat ; Vascular ; Smooth muscle ; Factor X ; Coagulation ; Clot
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A computational model was developed to investigate the contribution of classical mass transport and flow parameters to factor X (FX) activation by the tissue factor–factor VIIa complex (TF:VIIa) on one wall of a parallel-plate flow chamber. The computational results were compared to previously obtained experimental data for the generation of factor Xa (FXa) by TF:VIIa on the surface of cultured rat vascular smooth muscle cells. In this study, the complete steady-state convection–diffusion equation was solved using the commercial software package, FLUENT (Fluent Inc., Lebanon, New Hampshire). A user-defined subroutine interfaced with FLUENT implemented the surface reaction which was modeled using classical Michaelis–Menten reaction kinetics. The numerical solutions were obtained for 12 cases which used combinations of three wall shear rates and four reaction rates. The numerically obtained fluxes for a given reaction rate displayed a wall shear rate dependence which ranged from classical kinetic reaction control (no dependence) to pure diffusional control (maximum dependence). The experimental data, however, were not represented by numerical data generated using a single reaction rate. The three numerically obtained fluxes which corresponded most closely to the experimental fluxes were determined using three different V max values. This finding supports the hypothesis that there may be a direct effect of flow on the TF:VIIa complex or the cell membrane. © 1998 Biomedical Engineering Society. PAC98: 8722-q, 8710+e
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.120
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  • 10
    Electronic Resource
    Electronic Resource
    Estimation of Organ Transport Function from Recirculating Indicator Dilution Curves (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 128-137 
    Details
    ISSN: 1573-9686
    Keywords: Mannitol ; Deconvolution ; Mathematical model ; Transport function ; Recirculation ; Indicator dilution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The transport function of an indicator through an organ allows the calculation of important physiological parameters, but its estimation, especially in the presence of recirculation, can be difficult. In this paper, we estimate the transport function of 3H-mannitol (an extracellular tracer of glucose) in the human leg skeletal muscle. To do so, an indicator bolus is administered into the femoral artery and its recirculating dilution curves are nonuniformly sampled in both the femoral artery and the femoral vein. A new deconvolution-based method is used to simultaneously estimate the indicator transport function and the organ plasma flow. Subsequently, the indicator mean transit time and distribution volume are calculated. The reliability of the method is assessed by Monte Carlo simulation. The ability to estimate parameters, like mean transit time and extracellular distribution volume, is critical to the study of pathophysiologic states such as diabetes, insulin resistance, and hypertension. © 1998 Biomedical Engineering Society. PAC98: 8710+e, 0270Lq, 8745Hw
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.84
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  • 11
    Electronic Resource
    Electronic Resource
    Optical and Radioisotope Indicator Dilution Measurements in Pulmonary Edema (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 417-430 
    Details
    ISSN: 1573-9686
    Keywords: Capillary permeability ; Acute respiratory distress syndrome ; Mathematical model ; Alloxan lung injury ; Pulmonary edema ; Lung fluid balance ; Indicator dilution: optical ; Indicator dilution: radioisotope
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The objective of this study was a validation of an optical multiple indicator dilution technique for measuring microvascular exchange parameters in edematous lungs by comparison to conventional radioisotope multiple indicator dilution methods. Six anesthetized dogs were studied at baseline and after alloxan infusion to increase capillary permeability. In addition, 11 isolated, perfused dog lungs were studied at baseline and after edema was created by increasing venous pressure or by infusing alloxan to increase vascular permeability. Increased capillary permeability from alloxan infusion led to increases in most but not all capillary exchange parameters as analyzed by mathematical models and measured by both optical and radioisotope methods. Increased vascular pressure led to increased edema but no significant increases in capillary exchange parameters. Two-way analysis of variance (ANOVA; variations in baseline versus pressure or alloxan and variation in optical versus radioisotope for each transport parameter derived from the mathematical models) indicated few significant differences in capillary exchange parameters between optical and radioisotope measures. Newman–Keuls multiple comparison tests did uncover some variations between a few of the group-mean values derived from optical and radioisotope methods. However, optical and radioisotope parameter measurements were highly correlated for all studies regardless of the mathematical model used for analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.94
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