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  • 1
    Electronic Resource
    Electronic Resource
    Blood gas and acid-base balance during cardiopulmonary resuscitation by intrathroacic and abdominal pressure variations (1986)
    Springer
    Basic research in cardiology 81 (1986), S. 326-333 
    Details
    ISSN: 1435-1803
    Keywords: cardiopulmonary resuscitation ; thoracic pressure variations ; blood gases ; acid-base
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The blood gases and acid-base balance in a modified cardiopulmonary resuscitation (CPR) technique, based on intrathoracic and abdominal pressure variations by means of circumferential chest and abdominal balloon inflation, were examined in seven mongrel dogs. CPR proceeded for pcriods lasting 30 min or more and was monitored by measurements of aortic and right ventricular pressures and carotid blood flow during the compression (artificial systole) and the relaxation phase (artificial diastole). The carotid blood flow was 21.7±7.8 (mean±SD) ml/min, which was 0.18±0.6 (mean±SD) of the baseline mean carotid flow. Arterial blood was well oxygenated throughout the experiments, and low PCO2 levels (5–9 mm Hg) caused an initial severe alkalosis (pH=7.94). However, a gradual decline in the pH was observed, reaching a value of 7.34±0.11 in the arterial blood after 30 min of CPR. The venous blood had a very low oxygen content (less than 25.5%) with a low PO2 and a normal PCO2 (43.7±7.3 mm Hg) throughout the experiment. A gradually developing metabolic acidosis was reflected in the pH values, and an increase in base deficit from 2.25±5.6 meq/1 prior to CPR to 16.7±3.2 meq/1 after 30 min of CPR was observed. High arteriovenous differences in oxygen content (greater than 66.4%) and CO2 tension (30.1–41.5 mm Hg) with a slowly developing metabolic acidosis were noted. Thus, CPR by thoracic and abdominal pressure variations is associated with a slowly developing metabolic acidosis which is the result of the combination of hyperventilation and a low perfusion state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01907415
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  • 2
    Electronic Resource
    Electronic Resource
    Two-substrates packed-bed bioreactors: inhibition of enzyme and competitive binding of substrate and product to a ligand (1991)
    Springer
    Bioprocess and biosystems engineering 7 (1991), S. 115-121 
    Details
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract An analytical model is developed to describe the performance of a packed-bed immobilized enzyme reactor in which parallel processes take place. In particular, two-substrate reaction, inhibition of the enzyme by one of the reaction products, and binding of one substrate and/or one product to an added ligand are taken into account. In addition, substrates and product diffusion into the porous catalyst are also considered. Using this model, numerical simulations were performed. The results point to the fact that, when all the above processes occur concomitantly, a variety of performance characteristics can be obtained, depending on the particular values of the related parameters. Moreover, under certain conditions, the reactor performance can be improved by controlled addition of ligand.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00369422
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  • 3
    Electronic Resource
    Electronic Resource
    Heat and mass transfer in direct contact hygroscopic condensation (1987)
    Springer
    Heat and mass transfer 21 (1987), S. 233-245 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Es wird eine theoretische Analyse der hygroskopischen Kondensation eines kalten Dampfes auf heißem Film bei unmittelbarem Kontakt vorgestellt. Diese Kondensation bei relativ niedriger Temperatur, niedrigem Druck des Dampfes auf heißem Film einer hygroskopischen Sole-Lösung kann auftreten durch Druckerniedrigung über einer genügend hoch konzentrierten Lösung. Die treibende Kraft für die Kondensation ist der Unterschied zwischen dem Partialdruck des Wassers in der Sole und dem Partialdruck des kondensierenden Wasserdampfes. Die Kondensation wird auch durch gleichzeitig auftretende Stofftransportmechanismen gesteuert, resultierend aus einer nichtisothermen Absorption, die durch eine entgegengesetzte, thermische treibende Kraft in der kondensierenden Dampfphase ermöglicht wird. Das gesamte Verhalten wird bestimmt durch die akkumulierenden Effekte der verschiedenen Widerstände auf den Wärmeund den Stofftransport. Die vorliegende Studie hat zum Ziel, diese steuernden Mechanismen, die mit Absorptions- und Kondensationsprozessen verbunden sind, zu klären und es wird ein mittlerer Wärmeübergangskoeffizient für laminare und turbulente Strömungsbereiche vorgeschlagen.
    Notes: Abstract A theoretical analysis of direct contact hygroscopic-condensation of cold vapor on hot films is presented. The condensation of the relatively low temperature, low pressure, vapors on a hot film of an hygroscopic brine solution may occur due to the reduced vapor pressure of a sufficiently concentrated solution. The driving force for condensation is the difference between the partial pressure of water in the brine and the partial pressure of the condensing water vapor. The condensation is also governed by simultaneous mass transfer mechanisms, due to a non-isothermal absorption, with a possible opposing thermal driving force in the condensing vapor phase. The overall performance is determined by the accumulating effects of the various resistances to heat and mass transfer. The present study is aimed to elucidate the controlling mechanisms associated with this absorption-condensation process, and suggest overall transfer rates at the laminar and turbulent flow regimes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01004026
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  • 4
    Electronic Resource
    Electronic Resource
    A conical model to describe the nonuniformity of the left ventricular twisting motion (1992)
    Springer
    Annals of biomedical engineering 20 (1992), S. 149-165 
    Details
    ISSN: 1573-9686
    Keywords: Left ventricle ; Model ; Cone ; Twist ; Nonuniformity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The systolic contraction and fiber shortening in the left ventricle (LV) produces torsional moments in the myocardium, resulting in a gradient of angular displacements about the long axis. This is manifested as a counterclockwise rotation of the apex relative to the base, when viewed from the apex. Recent studies with magnetic resonance imaging (MRI), using noninvasive magnetic tags, have revealed three important properties of the LV twist: (a) The angle of twist (i.e., the angular rotation of a slice relative to the basal slice) is consistently higher at the endocardium as compared to the epicardium; (b) The twist increases towards the apex; and (c) Straight MRI-tagged radial lines at end-diastole (ED) are slightly curved at end-systole (ES), implying a nonlinear transmural variation of the twist. The present study suggests that the geometry of the LV at ES can be represented by a thick-walled hollow cone, and that the transmural twist patterns from ED to ES can be described using the continuum mechanics approach and a small strain analysis of an isotropic cone subjected to external torque. The predicted results are compared with the noninvasive MRI measurements of transmural twist in eight human volunteers. Given the epicardial angles of twist of each slice, the predicted endocardial angles of twist are in good correlation with the experimental findings (r=0.86, slope=1.09, SEE=4.1°). In addition, the model reliably describes the changes in the twist magnitude from apex to base (no significant difference from experimental values,P=0.2), and predicts the curvilinear pattern at ES of the originally straight ED radial lines. Thus, the conical model with uniform properties of the LV, reliably predicts the nonuniformity of the twist patterns, implying that the LV twist is strongly affected by LV geometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368517
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  • 5
    Electronic Resource
    Electronic Resource
    Characterization of regional left ventricular contraction by curvature difference analysis (1988)
    Springer
    Basic research in cardiology 83 (1988), S. 486-500 
    Details
    ISSN: 1435-1803
    Keywords: normalized curvature difference function ; curvature difference analysis ; left ventricle abnormality diagnosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A method which characterizes the contraction of the left ventricle (LV) by changes in the LV endocardial contour curvatures is presented. A normalized curvature difference function (NCDF) is defined by the difference between the (normalized) curvature functions of end diastolic (ED) and end systolic (ES) contours. Unlike wall-motion based procedures, NCDF is independent of any reference system and of the method used for ED-ES shape alignment. Normal and pathological diagnosis criteria were first established based on right anterior oblique (RAO) projection ventriculograms of a study group which included 58 normal and 28 abnormal patients. Patients with an infarcted myocardial region differed from the characteristic NCDF pattern of normals and exhibited regionally defined irregularities. The diagnosis criteria were then applied to a total of 159 patients in two groups in two independent laboratories. One group (in Israel) included 49 cases (20 normals, 29 abnormals); the second (in France) included 108 cases (48 normals, 60 abnormals). These two groups yielded similar sensitivity (97% and 97%) and specificity (90% and 100%) in detection of abnormality of the ventricle. When tested against other quantitative wall motion techniques, the NCDF shows a regional sensitivity of 95%, indicating that curvature difference analysis is a potential tool for the automatic and objective diagnosis of regional LV function abnormalities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01906678
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  • 6
    Electronic Resource
    Electronic Resource
    Flow field around collapsing bubble trains: Theoretical analysis (1971)
    Springer
    Flow, turbulence and combustion 24 (1971), S. 53-64 
    Details
    ISSN: 1573-1987
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A method of successive approximations is utilized to analyze the potential flow field around freely rising collapsing bubble trains. For simplicity, the analysis is confined to a two bubble column. An infinite series solution is obtained and the truncation errors are quantitatively analyzed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00411704
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  • 7
    Electronic Resource
    Electronic Resource
    Heat transfer in laminar flow in circular and flat conduits with (constant) surface resistance (1965)
    Springer
    Flow, turbulence and combustion 14 (1965), S. 157-171 
    Details
    ISSN: 1573-1987
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Graetz's solution is extended to include surface resistance to heat transfer in laminar flow in circular tubes and flat conduits. The computed eigenvalues, eigenfunctions, coefficients and average mean temperatures for various surface resistances are presented. The solution presented is general and contains Graetz's solution as a particular case of zero boundary resistance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00382240
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  • 8
    Electronic Resource
    Electronic Resource
    Cardiac assist by intrathoracic and abdominal pressure variations: A mathematical study (1984)
    Springer
    Medical & biological engineering & computing 22 (1984), S. 507-515 
    Details
    ISSN: 1741-0444
    Keywords: Cardiac assist ; Intrathoracic pressure variations ; Mathematical model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract A lumped parameter mathematical model of the complete cardiovascular system simulating cardiac assist by external pressure variations is presented. The various vascular compartments are assumed to have appropriate resistance, capacitance and inductance values. The right and left ventricles are represented by time varying capacitances reciprocal to the time varying elastances. The effects of external pressure variations on the circulation are evaluated for different modes of operation. Systolic thoracic pressure waves, diastolic abdominal pressure waves and a combination of both waves are shown to have a favourable effect on the circulation in cardiogenic shock. The different mechanism of cardiocirculatory assist involved are presented and discussed below
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02443863
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  • 9
    Electronic Resource
    Electronic Resource
    Mechanical pathophysiology of some heart diseases: a theoretical model study (1990)
    Springer
    Medical & biological engineering & computing 28 (1990), S. 237-248 
    Details
    ISSN: 1741-0444
    Keywords: Cardiac ; Left ventricle ; Model ; Pathophysiology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Sarcomere dynamics are related to the global left ventricular (LV) function in some representative pathological states, by using a theoretical model which combines sarcomere function, LV fibrous structure and geometry with the haemodynamic loading conditions. The analysis shows that pressure (concentric) hypertrophy due to hypertension or aortic stenosis is associated with an increase of the normal endocardial-to-epicardial gradient(s) of oxygen demand, which may be one of the causes for the development of endocardial fibrosis. The analysis also indicates that sarcomere shortening is relatively normal in compensated volume (eccentric) hypertrophy. Mitral stenosis demonstrates a case of decreased LV function, secondary to a chronic decrease in LV end diastolic volume, with sarcomeres that operate at their lowest length range. Conversely, the sarcomere function is depressed in cardiomyopathy; the heart's pumping function is maintained by appropriate adjustment mechanisms. However, the sarcomeres show minimal shortening and function at their highest length range with low (or zero) functional reserve. The study thus provides a quantitative tool that relates global LV function to local sarcomere dynamics in various pathological states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02442680
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  • 10
    Electronic Resource
    Electronic Resource
    Force interval relationship (FIR) related to the global function of the left ventricle: a computer study (1990)
    Springer
    Medical & biological engineering & computing 28 (1990), S. 446-456 
    Details
    ISSN: 1741-0444
    Keywords: Calcium kinetics ; Force interval relationship ; Left ventricle ; Model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract A model which relates the left ventricular (LV) geometry, structure and sarcomere properties to its global function, recently proposed by the authors, is extended to account for contractility changes which are a function of the heart rate, prematurity of the beat and calcium transients within the cell. To characterise LV function and relate it to fibre function under varying rhythm conditions, a model of muscle force restitution, based on calcium kinetics, was used to calculate the maximum fibre stress at the optimum sarcomere length σ0 as the parameter which depends on the heart rate, the test pulse interval TPI, the action potential duration APD and the restitution time constant. The global LV force interval relationship FIR was then calculated, and by comparing the calculated FIR to the experimental measurement (in dogs) at the ventricular level, the constants of the restitution of force at the fibre level were derived. Based on these constants, the LV function under ejecting conditions at various rhythm disturbances was calculated and related to the local, distributed parameters. This approach provides a tool to describe ventricular function as well as transmural distribution of stress and sarcomere length at a wide variety of loading and rhythm conditions based on given ‘muscle level’ parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441968
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