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  • 1
    Electronic Resource
    Electronic Resource
    Measurement techniques for unsteady flows in turbomachines (2000)
    Springer
    Experiments in fluids 28 (2000), S. 285-321 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  The growing interest for unsteady flows in turbomachines over the last two decades has led to an intensive development of fast response measurement techniques, capable of resolving with high frequency phenomena related to inlet distortion, rotating stall and blade row interference effects with blade passing frequencies ranging from 3 to 30 kHz. This development was favoured by major advances in sensor technology and data acquisition systems. The paper reviews the progress in fast response measurement techniques for high speed turbomachinery and application with emphasis on fast response pressure and temperature probes and blade surface sensors including pressure, heat transfer and shear stress determination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050390
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  • 2
    Electronic Resource
    Electronic Resource
    Deformation of the dog aortic valve ring during the cardiac cycle (1988)
    Springer
    Pflügers Archiv 412 (1988), S. 647-653 
    Details
    ISSN: 1432-2013
    Keywords: Aortic valve ; Commissure strain ; Base strain ; Commissure-base strain ; Inductive coils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Changes in strain in the line of aortic valve leaflet attachment (aortic ring) were measured during the cardiac cycle by means of an inductive technique. To that purpose coils were sutured to each commissure and base point of the aortic ring, when the animals were on a cardiopulmonary bypass. After bypass and stabilization of the hemodynamic variables changes in the aortic strain were measured at aortic pressures ranging from 4 to 20 kPa. Aortic pressure at the level of the commissure points and left ventricular pressure were measured to assess transvalvular pressure. Commissure strain appeared to depend on aortic and transvalvular pressure throughout the cardiac cycle. At an aortic pressure of 10 kPa (75 mm Hg), the derivative of commissure strain to aortic pressure was found to be 1.9×10−5±1.2×10−5 Pa−1 (mean ±SD). During the ventricular ejection phase commissure strain was 0.04±0.03 higher than during ventricular filling. Maximum variations in basal strain during the cardiac cycle ranged from 0.03 to 0.15. During the ejection phase the basal segments adjoining the myocardium shortened whereas the segment close to the non-contracting anterior mitral valve leaflet lengthened. Strain between a base and a commissure point of the aortic ring were synchronous with the cardiac cycle, but no specific pattern could be found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00583767
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of pyruvate on post-ischemic myocardial recovery at various workloads (1988)
    Springer
    Pflügers Archiv 413 (1988), S. 167-173 
    Details
    ISSN: 1432-2013
    Keywords: Pyruvate ; Transient ischemia ; Adenine nucleotides ; Enzyme release ; Workload ; Working rat heart
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In the present study the hemodynamic and metabolic effects of pyruvate (5 mM), added as cosubstrate to glucose (11 mM) perfused, transiently ischemic, isolated working rat hearts, were evaluated. During 2 h of normoxic perfusion pyruvate improved functional stability, prevented depletion of glycogen and triacylglycerol stores, and increased non-esterified fatty acid (NEFA) levels, even at relatively high workloads. The elevated NEFA levels are in line with the notion that pyruvate competes with endogenously produced fatty acids for oxidative energy production. After 45 min of global ischemia pyruvate was found (a) to affect markedly the relative contribution of ATP, ADP and AMP to the total adenine nucleotide content and (b) to stimulate the degradation of glycogen and to enhance the accumulation of lactate, suggesting enhanced anaerobic ATP rroduction. After restoration of flow pyruvate reduced the incidence of fibrillation and markedly improved recovery of cardiac output at both normal and high workload. Pyruvate did neither attenuate the release of lactate dehydrogenase, a marker for cell death, nor improve the conservation of the total adenine nucleotide and ATP content of hearts reperfused for 30 min. The latter findings indicate that hemodynamic recovery during reperfusion in the presence of pyruvate is neither related to the absolute tissue content of ATP nor to a reduction of irreversible cell damage, and suggest that pyruvate exerts its advantageous hemodynamic effects rather by improving the condition of reversibly damaged cells during reperfusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582527
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  • 4
    Electronic Resource
    Electronic Resource
    An improved isolated, left ventricular ejecting, murine heart model (1999)
    Springer
    Pflügers Archiv 437 (1999), S. 182-190 
    Details
    ISSN: 1432-2013
    Keywords: Key words Isolated murine heart ; Antegrade perfusion ; Functional stability ; High-energy phosphates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  An improved, isolated, left ventricular-ejecting, murine heart model is described and evaluated. Special attention was paid to the design and impedance characteristics of the artificial aortic outflow tract and perfusate composition, which contained glucose (10 mM plus insulin) and pyruvate (1.5 mM) as substrates. Temperature of the isolated perfused hearts was maintained at 38.5 °C. During antegrade perfusion (preload 10 mm Hg, afterload 50 mm Hg, 2.5 mM Ca2+) proper design of the aortic outflow tract provided baseline values for cardiac output (CO), left ventricular developed pressure (LVDP) and the maximum first derivative of left ventricular pressure (LV dP/dt max) of 11.1±1.7 ml min–1, 83±5 mm Hg and 6283±552 mm Hg s–1, respectively, resembling findings in the intact mouse. During 100 min normoxic antegrade perfusion CO declined non-significantly by less than 10%. Varying pre- and afterloads resulted in typical Frank-Starling relationships with maximal CO values of 18.6±1.8 ml min–1 at pre- and afterload pressures of 25 and 50 mm Hg, respectively. Left ventricular function curves were constructed at free [Ca2+] of 1.5 and 2.5 mM in the perfusion medium. Significantly higher values for CO, LVDP and LV dP/dt max and LV dP/dt min were obtained at 2.5 mM Ca2+ at all loading conditions investigated. Phosphocreatine and creatine levels remained stable throughout the perfusion period. Despite a small but significant decline in tissue ATP content, the sum of adenine nucleotides did not change during the normoxic perfusion period. The tissue content of glycogen increased significantly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050767
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  • 5
    Electronic Resource
    Electronic Resource
    Model of the coronary circulation based on pressure dependence of coronary resistance and compliance (1988)
    Springer
    Basic research in cardiology 83 (1988), S. 510-524 
    Details
    ISSN: 1435-1803
    Keywords: coronary circulation model ; intramyocardial compliance ; diastolicpressure-flow curves ; coronary resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of pressure-dependent changes in vascular volume, resistance and capacitance in the coronary micro-circulation, has been studied by a distributed mathematical model of the coronary micro-vasculature in the left ventricular wall. The model does not include regulation of coronary blood flow and is evaluated only for the fully dilated coronary vasculature. The left ventricular wall was thought to consist of eight parallel layers, each of them with an arteriolar, capillary and venular compartment. The resistance of each vessel was thought to depend on the inverse of squared volume, according to Poiseuille's Law for tubes with constant length. Tissue pressure has been assumed to be equal to left ventricular cavity pressure at the endocardium and to decrease linearly to atmospheric level at the epicardium. The pressure-volume relation of the vessel compartments were assumed to be sigmoidal. There is a rest volume at transmural pressure zero and ΔV/ΔP decreases with increasing transmural pressure. Simulation of experimental protocols described by other authors yielded results which were similar to the experimental outcomes, illustrated by: (1) a parallel shift to the flow axis of the pressure-flow curves due to cardiac arrest (2) steady-state endo/epi ratio of flow as a function of heart rate. It is concluded that interpretation of transients in coronary flow and/or pressure by models containing fixed resistance and capacitance may seriously underestimate intramyocardial capacitative effects and characteristic time constants for pressure-induced resistance changes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01906680
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  • 6
    Electronic Resource
    Electronic Resource
    Optimization of Cardiac Fiber Orientation for Homogeneous Fiber Strain During Ejection (1999)
    Springer
    Annals of biomedical engineering 27 (1999), S. 289-297 
    Details
    ISSN: 1573-9686
    Keywords: Left ventricle ; Finite-element analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The strain of muscle fibers in the heart is likely to be distributed uniformly over the cardiac walls during the ejection period of the cardiac cycle. Mathematical models of left ventricular (LV) wall mechanics have shown that the distribution of fiber strain during ejection is sensitive to the orientation of muscle fibers in the wall. In the present study, we tested the hypothesis that fiber orientation in the LV wall is such that fiber strain during ejection is as homogeneous as possible. A finite-element model of LV wall mechanics was set up to compute the distribution of fiber strain at the beginning (BE) and end (EE) of the ejection period of the cardiac cycle, with respect to a middiastolic reference state. The distribution of fiber orientation over the LV wall, quantified by three parameters, was systematically varied to minimize regional differences in fiber shortening during ejection and in the average of fiber strain at BE and EE. A well-defined optimum in the distribution of fiber orientation was found which was not significantly different from anatomical measurements. After optimization, the average of fiber strain at BE and EE was 0.025 ± 0.011 (mean ± standard deviation) and the difference in fiber strain during ejection was 0.214 ± 0.018. The results indicate that the LV structure is designed for maximum homogeneity of fiber strain during ejection. © 1999 Biomedical Engineering Society. PAC99: 8719Hh, 8710+e, 8719Ff, 8719Rr, 0270Dh
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.147
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  • 7
    Electronic Resource
    Electronic Resource
    On the consistency of four different control surfaces used for finite area blade-to-blade flow calculations (1984)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 4 (1984), S. 1083-1095 
    Details
    ISSN: 0271-2091
    Keywords: Turbomachines ; Finite Volume ; Consistency ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The aim of this contribution is to investigate the consistency and order of accuracy of different control surfaces used for finite area blade-to-blade flow calculations. The following cases will be treated: a hexagonal element, a trapezoidal element, a bitrapezoidal element and a quadrilateral element. Finally, the consistency conditions will be discussed and compared with respect to a cascade flow application.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650041107
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  • 8
    Electronic Resource
    Electronic Resource
    Analysis of the bidirectional optical three-stage prism grating system for red blood cell velocity measurements in microvessels (1984)
    Springer
    Medical & biological engineering & computing 22 (1984), S. 521-528 
    Details
    ISSN: 1741-0444
    Keywords: Microcirculation ; Red blood cell velocity ; Spatial filtering ; Three-stage prism grating
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract A bidirectional optical (BDO) three-stage prism grating system has been developed to measure online direction and magnitude of red blood cell (RBC) velocities in the microcirculation. The paper describes a mathematical evaluation of the BDO system. The optical grating configuration was simulated in terms of a spatial filter. The input signal was the simulated spatial light distribution of a group of moving RBCs Three methods for estimating the mean frequency (fmean) of the signal corresponding to RBC velocity were evaluated on the criteria of accuracy and noise sensitivity. All underestimated the RBC velocity. The reference method calculates fmean from the power density spectrum. A zero-crossing counting technique and a method based on time differentiation underestimated the mean frequency by 14·1±11·3 per cent (mean ±SD) and 0·9±0·1 per cent, respectively. The zero-crossing counting technique was more sensitive to noise than both other methods. The reference method, operating in the frequency domain, is preferred, because the power density spectrum obtained can be corrected for filtering errors induced by higher-order passbands of the optical filter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02443865
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