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  • Articles  (12)
  • Springer  (12)
  • 1975-1979  (12)
  • Technology  (12)
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  • Articles  (12)
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  • 1
    Electronic Resource
    Electronic Resource
    An intravascular test device for thromboresistant materials: Analysis and preliminary experimental evaluation (1975)
    Springer
    Annals of biomedical engineering 3 (1975), S. 322-341 
    Details
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The interaction of artificial materials with the process of thrombus formation in blood depends on geometric and fluid-mechanical factors as well as the proximity of even slightly injured tissue. A test device that takes account of these factors and is suitable for intravascular implantation is described. The device effects a division of total flow between a tube oriented on the vessel axis, whose diameter is less than that of the vessel, and the annular space between the tube and vessel. Dimensions are chosen to effect thrombogenesis preferentially within the tube. The division of flow is calculated as a function of dimensional ratios and Reynolds number. Other aspects of the fluid dynamical performance of the device are discussed. Results of experimental evaluations in an extracorporeal shunt are reported; they show preferential deposition where expected, small variations among similar experiments, and good ability to distinguish among different materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02390977
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  • 2
    Electronic Resource
    Electronic Resource
    A permutation test for periodicities in short, noisy time series (1975)
    Springer
    Annals of biomedical engineering 3 (1975), S. 160-180 
    Details
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract We developed a distribution-free, nonparametric statistical test (the permutation-rank test) for verifying the exiscence of significant peaks in power spectral ordinates calculated on noisy, short, time series. In this paper, we demonstrate the application of the test in the case of periodic series generated by the in numero perturbation of the amplitude of a cosine wave of known, single, constant frequency. The test was able to detect the underlying oscillation when it was amplitude-corrupted by noise generated by a standard uniform distribution, with a noise-to-signal ratio of 1 or less. It was shown that the permutation test generated a white process from the time series being tested. We concluded that any time series, if sampled for the periodicities of interest in a manner appropriate for the constraints imposed by the Nyquist theorem in the presence of unwanted random signal (noise), is suitable for standard time series analysis and application of this new permutation test for the significance of a spectral ordinate. The advantages of the new test over the standard methods are that it requires no assumptions about the data; does not require replicate analysis of a reference sample; takes into account both observation and system noise; and, at least in some instances, is more sensitive.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02363068
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  • 3
    Electronic Resource
    Electronic Resource
    A four phase model of capillary tracer exchange (1979)
    Springer
    Annals of biomedical engineering 7 (1979), S. 203-238 
    Details
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract In previously proposed models of capillary tracer exchange, red cell membranes have usually been assumed tobe either infinitely permeable or completely impermeable to tracer molecules. Permeability of the extravascular cellular compartment has been treated previously, but never in conjunction with finite capillary and red cell permeability effects. Our objective was to examine the situation encountered with multiple indicator experiments in which tracer exchange may be limited by red cell, tissue and capillary membranes. A four phase model is presented which accounts for plasma, red cell, interstitial, and extravascular cellular regions. Results from this model indicate that transcapillary tracer exchange is affected by a minimum of seven dimensionless parameters. The influence of relatively low red cell permeability is most pronounced when the dimensionless capillary permeability is high (i.e., αcap ⩾ 1). Deviations in transcapillary extraction values from those corresponding to infinitely permeable erythrocytes can be kept below 5% when capillary permeability is low (i.e., αcap ⩽ .15) by pre-equilibrating the injectate with tracer prior to injection. The additional barrier in the extravascular region necessarily decreases overall transvascular tracer exchange but does not affect extraction values in the vicinity of the appearance time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02364115
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  • 4
    Electronic Resource
    Electronic Resource
    A model of the mechanics of the left ventricle (1979)
    Springer
    Annals of biomedical engineering 7 (1979), S. 299-318 
    Details
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The relation between cardiac muscle mechanics and left ventricular (LV) pump function is simulated by a mathematical model. In the following article special attention is paid to the relation between LV pressure and LV volume on the one hand and the transmural distribution of sarcomere length and fiber stress on the other. The LV is simulated by a thick-walled cylinder composed of 8 concentric shells. The myocardial material is assumed to be anisotropic. The orientation and sequential activation of the muscle fibers across the LV wall are considered per shell. Twisting of the base with respect to the apex around the axis of the LV is simulated by rotation of the upper cross-sectional surface of the cylinder with respect to the lower one aroud the axis of the cylinder. The model reveals that twisting of the LV is an important means to equalize transmural differences in sarcomere shortening and end-systolic fiber stress. When torsion is allowed, transmural differences in sarcomere shortening and end-systolic fiber stress are less than 18% and 16%, respectively. When torsion is prevented as in most of the models of LV-mechanics described in literature, these transmural differences increase up to 32% and 42%, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02364118
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical analysis of the effects of diffusivity on pulmonary gas transport and mixing (1979)
    Springer
    Annals of biomedical engineering 7 (1979), S. 375-386 
    Details
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The effects of different tracer gas diffusivities upon pulmonary gas transport and mixing have been examined by means of a physico-mathematical lung model. Specifically, it is demonstrated how the expired alveolar plateau slope of a tracer gas gives an indication of the magnitude of the end expiratory concentration differences existing in the acinus. Further, by modifying the initial analysis slightly (to allow for a finite flux of gas across the alveolar wall) it has been indicated how more marked stratified inhomogeneities are associated with the transport of soluble rather than isoluble tracer gases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02364216
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  • 6
    Electronic Resource
    Electronic Resource
    Two models of glomerular filtration rate and renal blood flow in the rat (1975)
    Springer
    Annals of biomedical engineering 3 (1975), S. 72-99 
    Details
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Two mathematical models of glomerular filtration and blood flow are derived. The first is based on principles of fluid and mass conservation in individual capillaries. The model explains why the filtration rate (GFR) is strongly dependent on local hydrostatic and protein oncotic pressures, and on plasma flow rate (GCPF), but only weakly dependent on exact numbers, lengths, radii, or filtration coefficient of glomerular capillaries. The model shows that much of the increased GFR in both isooncotic plasma loading and isotonic Ringer's loading is due to increased GCPF caused by diluting erythrocytes. The second model uses several approximations and reduces to a quadratic in afferent arteriolar blood flow. When arterial pressure, hematocrit, plasma protein concentration, and afferent and efferent arteriolar resistances are specified, the model predicts GFR, afferent arteriolar blood flow, and filtration fraction. Alternatively, if any two of these three variables are known, the model predicts segmental arteriolar resistances. The model indicates that GFR and blood flow regulation must be located in the afferent arteriole, despite the strong dependence of GFR on GCPF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00000006
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  • 7
    Electronic Resource
    Electronic Resource
    Detection by a permutation test of periodicities in biological time series: Dependence of sensitivity on measurement precision (1976)
    Springer
    Annals of biomedical engineering 4 (1976), S. 68-77 
    Details
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A statistic is defined from the analysis of variance of replicate measurements in biological time series data. This statistic, the square root of the mean square of the variation within groups of two replications, is termed the index of replication,S Δ, and is a measure of the precision of an assay.S Δ was found to be a better indicator of assay replicability than the conventional index of assay precision, λ, calculated from duplicate standard curves. When a power spectrum permutation test, as defined elsewhere, is used to detect a significant periodicity in discrete, amplitude-noisy, time series data, the relationship betweenS Δ and the 95% confidence limit on peak-to-peak signal variation shows that the variation must be greater than 1.4S Δ for detection. Since the value of 1.4S Δ assumes duplicate determinations per point and a uniform distribution of measurement error, it is a conservative estimate of the strength of the power spectrum permutation test to detect one frequency. When a conventional analysis of variance is used, the level of 1.4S Δ is not reached until quadruplicate determinations have been processed; thus, the present approach is more efficient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02363559
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  • 8
    Electronic Resource
    Electronic Resource
    Alternative futures for biomedical research (1979)
    Springer
    Annals of biomedical engineering 7 (1979), S. 1-44 
    Details
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02364437
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  • 9
    Electronic Resource
    Electronic Resource
    The effects of red cell and tissue exchange on the evaluation of capillary permeability from multiple indicator data (1979)
    Springer
    Annals of biomedical engineering 7 (1979), S. 239-282 
    Details
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The two phase (vascular-extravascular) Sangren-Sheppard (SS) model is often used to estimate capillary permeability-surface area product (PS) from multiple indicator data. Our objective was to identify conditions where erroneous estimates of capillary PS or extravascular volume (VE) result from the application of this model to data obtained from non-homogeneous capillary units. We used a 4-phase capillary-tissue model (plasma, erythrocytes, interstitial fluid and extravascular cellular fluid) to simulate data collected from a heterogeneous capillary unit. A moment-matching technique was used to compute the parameters of the simpler SS model which would adequately describe the 4 phase tracer concentration-time (c(t)) curve. Deviations of computed values of VE and PS from the PS and extravascular volume specified in the 4-phase model were determined as functions of dimensionless red cell permeability αRC, hematocrit value, plasma-to-red cell velocity ratio, dimensionless extravascular cellular volume and permeability, capillary permeability αcap, and the fraction of indicator orginally deposited in the plasma at the capillary inlet. Our results indicate that application of the SS model to simulated low capillary permeability data produces underestimates in both VE and PS. Equations are presented which correct for this effect so long as the SS and 4-phase model c(t) curves are similar. Application of the whole blood-tissue SS model in situations where red cells are only slightly permeable or use of the plasma-tissue SS model when red cells admit tracer can lead to significant errors in VE and PS estimates. When αcap is relatively large neither SS model yields an accurate estimate of PS in the intermediate αRC range (i.e., near unity). Less than 10% error will result, regardless of αRC, if the blood-tissue SS model is used (αcap ≤ .30, Hct≤.50) and the tracer is equilibrated with a blood sample before injection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02364116
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  • 10
    Electronic Resource
    Electronic Resource
    Stimulator for the isolated phrenic nerve diaphragm preparation (1978)
    Springer
    Annals of biomedical engineering 6 (1978), S. 78-81 
    Details
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A simple and inexpensive stimulator is described to deliver regular impulses of alternating characteristics suitable for direct and indirect stimulation of an isolated phrenic nerve diaphragm preparation. Output impedances of 5 and 10 ω provide independence of pulse size and shape from load characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00000007
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