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D Lerche

Publications and source records attributed to D Lerche.

76 records · Page 5Linked to original sources
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The superposition of steady on oscillatory shear and its effect on the viscoelasticity of human blood and a blood-like model fluid.

To understand the pulsatility of human blood flow in vivo, it is necessary to separately investigate (1) steady shear and oscillatory flow, and (2) the superposition of steady shear flow on oscillatory flow performed under in vitro conditions. In this study a variable steady shear rate was superimposed in parallel on oscillatory shear at a constant frequency (0.5 Hz) for human blood (45% hematocrit), and an aqueous polyacrylamide polymer solution (AP 30E, concentration 300 ppm). The effect of superposition of the above two shear flows on the viscoelasticity of blood was more pronounced for the elastic (eta") than for the viscous (eta') component of viscoelasticity. With increasing superimposed shear rate, both eta' and eta" decreased, especially at the low shear region. This behavior can be explained by the viscoelastic properties of blood and the phenomenon of blood aggregation and disaggregation. Quantitatively, the dependence of the viscous component of complex viscosity on superimposed shear for both blood and polymer solution is described by a modified Carreau equation. The elastic component of complex viscosity decreased exponentially with increasing superimposed shear, and it is described by an exponential model.

Blood Viscosity↗
PubMedDate not supplied

[Sedimentation analyser--calibration and testing of a newly developed device for recording separation behavior of blood and other dispersed systems].

A computer-aided sedimentation analyser is described, which can be used for the continuous monitoring of the separation of blood and other dispersed systems by recording the separation-dependent infrared transmission in the range between 100 xg to 700 xg. Up to eight samples can be measured simultaneously within a short period of time, and only a small amount of suspension is required (15 minutes, 350 microliters). For centrifugal acceleration more than 100 xg and a haematocrit range of between 0.2 and 0.7, the evolution of the height of the plasma column (HPC) over time is expressed in non-linear regression form by HPC(t) = HPC infinity*(1-e-kt) + c. The separation constant k is influenced by plasma viscosity, haematocrit, aggregability and erythrocyte deformability, is directly proportional to centrifugal acceleration, and declines in hyperbolic fashion with increasing haematocrit between 300 xg and 650 xg. The separation constant is closely related to the maximum velocity which, in fact, represents the sensitive parameter of separation. Thus, the sedimentation analyser can be applied as an alternative to the traditional measurement of erythrocyte sedimentation rate according to Westergren.

Blood Sedimentation↗