D. Lerche

The effect of parallel combined steady and oscillatory shear flows on blood and polymer solutions

Human blood at physiological volume concentration exhibits non-Newtonian and thixotropic properties. The blood flow in the microcirculation is pulsatile, initiated from the heart pulse and can be considered as superposition of two partial flows: a) a steady shear, and b) an oscillatory shear. Until now steady and viscoelastic behavior were separately investigated. Here we present the response to the combination of steady and oscillatory shear for human blood, a high molecular weight aqueous polymer solution (polyacrylamide AP 273E) and an aqueous xanthan gum solution. The polyacrylamide and xanthan solutions are fluids that model the rheological properties of human blood. In general, parameters describing blood viscoelasticity became less pronounced as superimposed steady shear increased, especially at low shear region and by elasticity, associated with reduction in RBC aggregation. The response of polymer solutions to superposition shows qualitative similarities with blood by elasticity, but their quantitative response differed from that of blood. By viscosity another behavior was observed. The superposition effect on viscous component was described by a modified Carreau equation and for the elastic component by an exponential equation.

Moderate heat treatment of only red blood cells (RBC) slows down the rate of RBC-RBC aggregation in plasma.

Rouleau formation by back scattered light and flow behaviour by viscometry of heat-treated (48.4, 48.8 and 49.5 degrees C) and normal (37 degrees C) human red blood cells (RBC) were investigated. Washed RBC were treated in PBS and afterwards resuspended in their own plasma. It was found that the time behaviour of the fibrinogen mediated weak RBC-RBC interaction is influenced (decreased) already at an incubating temperature of 48.4 degrees C. Kinetic measurements are more sensitive than a static aggregation characterization. Beside the decreased deformability of the RBC also a heat-altered structure of the RBC-glycocalyx and the aggregating energy of the macromolecules have to be considered.

Modelling Hemodynamics in Small Tubes (Hollow Fibers) Considering Non-Newtonian Blood Properties and Radial Hematocrit Distribution

Velocity profiles and capillary volumetric flow were deduced from Navier-Stokes-equation accounting the non-Newtonian blood viscosity and its hematocrit dependence. Special attention was paled to the influence of the radial hematocrit distribution on radial flow pattern and the axial pressure drop.

Erythrocyte deformability of patients with chronic ischemic heart disease (cIHD) investigated by a modified capillary-rigidometer

The aim of this paper is to demonstrate by in-vitro experiments the sensitivity of parameters obtained, and to examine the RBC deformability ex-vivo of patients with cIHD as a consequence of coronary artery disease

Topo-optical investigations of human erythrocyte glycocalyx conformational changes induced by dextran

Cell surface properties are involved in the aggregation process of red blood cells. Using the topo-optical toluidine blue reaction, conformational changes of the glycocalyx (main component glycophorin A) were found when red blood cells were incubated and fixed in the presence of dextran. Relative differences in optical path as a measure of red blood cell membrane anisotropy decreased in relation to dextran concentration during fixation. These conformational changes could not be detected by electrophoretic measurements. When incubating, fixing and staining red blood cells in the presence of dextran, anisotropy decreased only at low dextran concentrations and increased at rising dextran concentrations. This biphasic course of differences in optical path seems to be due to different effects of dextran superimposing upon each other: a disturbing influence on the spatial order of sialic acid carrying oligosaccharide side chains due to H-bond interaction, and an increase in the size of dye aggregates and suppression of the thermal motion of macromolecules at higher dextran concentrations.

Mechanische Hämolyse durch künstliche Organe – Vergleichbarkeit von In-vitro-Hämolyseuntersuchungen und ihre Übertragbarkeit auf die Verhältnisse in vivo - Mechanical Hemolysis by Artificial Organs – Comparison of In Vitro Hemolysis Measurements and Transfer to In Vivo Behaviour.

Zur Charakterisierung der mechanischen Hämolyse durch Implantate oder Apparate (künstliche Herzklappen, Blutpumpen u. a.) unter In-vitro-Bedingungen wird i. a. der Anstieg der Hämoglobinkonzentration in der Blutprobe gemessen. Da das Ergebnis des Experiments durch die herrschenden Versuchsbedingungen mitbestimmt wird, kann es nicht als hämolytisches Potential des Implantats oder der Apparatur verwendet werden. Ein Vergleich mit Ergebnissen anderer Untersuchungen oder ihrer Übertragung auf die Verhältnisse in vivo sind daher i. a. nicht möglich. Im folgenden wird auf der Grundlage einer dem Ähnlichkeitsprinzip genügenden, von willkürlichen Einflüssen unabhängigen Kennzahl (Lysezahl) ein Konzept zur Behandlung komplexer hämolytischer Prozesse vorgestellt. Es beruht auf folgenden Schritten: 1. Definition der Lysezahl als Wahrscheinlichkeit der Zerstörung einer roten Blutzelle bei deren einmaliger Teilnahme an einem einfachen, hämolytisch wirksamen Prozeß. 2. Bereitstellung von Regeln, mit denen das komplexe hämolytische Geschehen einer realen Strömungssituation durch Serien-, Parallelund regurgitative Verkettung von einfachen hämolytischen Prozessen modelliert werden kann. 3. Experimentelle Bestimmung der Lysezahlen der beteiligten einfachen Prozesse. 4. Berechnung der effektiven Lysezahl des komplexen Systems unter Verwendung der Verkettungsregeln. 5. Übertragung des Ergebnisses auf die Verhältnisse in vivo durch eine Bilanzierung des Gleichgewichts von Erythropoese, mechanischer Hämolyse und natürlichem Zellabbau.

Hydrodynamischer In-vitro-Vergleich einer neuen künstlichen Herzklappe mit der Björk-Shiley-Klappe (Standard) - Hydrodynamic In-vitro Comparison of a New Artificial Heart Valve with the Björk-Shiley Valve (Standard)

Measurements performed to compare a newly developed tilting disc valve with the Björk-Shiley valve included velocity profiles downstream of the heart valves, valve-induced flow turbulence and pressure drop across the opened valves. The velocity profiles measured with pulsed Doppler ultrasound are similar, although they do not permit a quantitative comparison of the valves. The interpretation of the 90 degrees-component of Doppler signals as a measure of the turbulence permits a quantitative comparison without the need for extensive measurements. However, only large vortices are recorded, so that our turbulent shear stresses are lower than these reported in the literature. The pressure drop across the opened valve is a measure of the energy loss, and important parameters for the valve can be derived from it. The pressure drop is dependent on the test conditions, and is therefore not a characteristic constant of the valve. The transformation of the power law Q = C delta P beta into a relation between Re- and Eu-number gives a nondimensional similarity number that is characteristic for tilting disc valves. Its verification requires more investigations, involving variation of valve size and the viscosity of the test fluid.

The Influence of Rheological Properties of Test Fluids on the Flow Pattern Inside the Artificial Ventricle (Type Rostock) and in the Aortic Outflow Tract

The investigation of the flow pattern inside artificial ventricles and downstream of heart valve prostheses gives indications to the hydrodynamic optimization of such systems. The turbulent and laminar shear stresses within show strong local variations. The degree of damage of the blood components and the wall epithel depend on the value and duration of stresses.

Fission and refusion of red blood cells using a micropipette technique.

In micropipette experiments with small capillaries and moderate high pressure difference (approximately 1000 Pa) cell fragmentation (fission) of human red blood cells without hemolysis was observed by TV-system for a large number of fresh red blood cells of different donors. After separation, the fragment moves away from the residual cell. In seven cases this process was evaluated quantitatively and was shown that the rate of the fragment was constant in time. Two mechanisms for this phenomenon are discussed. In particular cases a spontaneous re-fusion with the residual cell body in the capillary can be observed. In our opinion probably protein-depleted membrane surfaces arise and membrane fusion is possible simply by mechanical contact without additional electric fields and/or fusion agents.

Die Überwachung der therapeutischen Plasmapherese mit physikalischen Meßverfahren - eine Grundlage zu ihrer mathematischen Modellierung

Humbold t -Unive r s i t ä t Berlin (Char i te ) , Schumannstr ; 20/21, Ber l in , 1040, ( . ) Inst i tut für medizinische Physik und Biophysik ( e i ) Kl in ik f ü r Innere Medizin Z u s a m m e n f a s s u n g Die Ü b e r w a c h u n g des V e r l a u f s der Membranplasrnaseparat ion ( M P S ) , insbesondere bei P a t i e n t e n mi t Hyperviskosi tätssyndrom ( H V S ) , e r fo lg te sowohl mit physikalischen M e ß v e r f a h r e n (Dichte 9 t dynamische Viskosität o? ) sowie durch Proteinbestimmungen. Die Ergebnisse von zwei HVS-Patienten werden exemplarisch dargestellt; und ^ sind geeignete Meßgrößen zur Verlaufsbeurteilung und -planung der MPSi Die zeitlichen Dich teänderungen sind durch ein kinetisches Modell beschreibbar.