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  • 1
    ISSN: 1573-9686
    Keywords: Digital angiography ; Residue detection ; Mean transit time ; Pulmonary circulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Methods for estimating regional flow from digital angiography or dynamic computed tomography images require determination of indicator mean transit time ( $$\bar t$$ ) through a region-of-interest (ROI). We examine how the ROI kinematics and input dispersion influence the recovery of $$\bar t$$ using a computer-simulated vessel network representing that which might occur in a real organ. The network simulates flow through a large artery branching into two small arteries, each feeding a system of smaller vessels intended to represent capillaries and small vessels below the resolution of the imaging system. The capillaries are drained by a similar system of veins. Concentration curves measured over the inlet to the network and microvascular ROI residue curves are simulated. When the area-height ratio of the microvascular ROI curve is used and all of the indicator is contained within the ROI for at least one time point, $$\bar t$$ is recovered exactly. As the size of the ROI is reduced or the inlet concentration curve becomes more dispresed, the error in the recovery of $$\bar t$$ grows. By first deconvolving the inlet concentration curve from the microvascular ROI curve, and then calculating the area-height ratio, $$\bar t$$ is recovered accurately. If the inlet concentration curve becomes more dispersed between its measured site and the actual inlet to the ROI, or if the flow distribution within the ROI is changed, the estimation of $$\bar t$$ can be degraded. To put the simulations in perspective relative to an example of image data, the methods were applied to microfocal x-ray angiography data obtained from a ⊃700 μm canine pulmonary artery and vein, the surrounding microvasculature and the inlet lobar arterial cannula.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Annals of biomedical engineering 28 (2000), S. 835-835 
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-9686
    Keywords: Pulmonary endothelium ; Carrier-mediated transport ; Michaelis-Menten equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The pulmonary endothelium is capable of removing and metabolizing serotonin (5HT) carried in the venous blood. Thus the lungs can influence the arterial concentrations of 5HT. In addition, there is evidence that changes in the lung uptake of 5HT might portend more serious endothelial damage wherein the barrier function of the endothelium is compromised. This has been a stimulus for finding methods for evaluating these endothelial functions. These methods must be able to distinguish changes in whole organ function which result from changes in perfusion (e.g., cardiac output, redistribution of flow, etc.) from those resulting from changes in the function of the endothelial cells. When a bolus containing radio-labeled 5HT and an unmetabolizable indicator which is confined to the vascular space is injected into the pulmonary artery, the pulmonary venous or systemic arterial concentration curves contain information about both the convective transport and endothelial cell process involved. Some of this information can be interpreted quantitatively using a simple mathematical model.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-9686
    Keywords: Saturable transport ; Endothelial metabolism ; Michaelis-Menten equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Certain substrates are rapidly taken up and/or metabolized by pulmonary endothelial cells in a saturable process. When such a substrate and a reference indicator are included in a bolus which is injected into the blood flowing into the lung, the extraction ratio, E(t), curves measured in the pulmonary venous outflow are asymmetric with respect to the reference indicator curve. If a sufficient quantity of substrate is included in the bolus, the extraction curves are concave upward. The shapes of the E(t) curves contain information regarding the chemical-physical processes which govern the fate of the substrate during its single passage through the lung. To interpret the shapes, computer simulations are used to illustrate separately the effects of the uptake of substrate into the cell, the returning flux of the substrate from the cell, the saturation phenomena of the extraction process, and the perfusion heterogeneity of the capillaries. Lastly, a simple analytical method for estimating the organ kinetic parameters of the extraction process is presented.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A theoretical and experimental investigation of a water jet impinging on a melting solid surface has been carried out. Ice, octane, p-xylene, and olive oil served as the meltable solid materials, comprising a Prandtl number range of 5 to 2 800. An available laminar stagnation flow model was utilized to describe melting heat transfer in the jet impingement region. Melting rate measurements were found to agree quite well with the values predicted with this model.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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