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D Lerche

Publications and source records attributed to D Lerche.

At least 37 records · Page 2Linked to original sources
PubMed1991

Time-dependent elastic extensional RBC deformation by micropipette aspiration: redistribution of the spectrin network?

The time dependence of small elastic extensional RBC deformation by micropipette aspiration has been analyzed. This process shows two-phases which are characterized by time constants of the order of some tenths of seconds and about ten seconds, respectively. The equilibrium tongue length is reached after about 30 s. For the first, fast step we assume that the membrane model of immobilized boundaries holds, i.e., the skeleton is tightly associated with the lipid bilayer and no redistribution of the skeleton with respect to the lipid bilayer is allowed. This lipid-spectrin interaction or anchorage is characterized by some association force density. It has been shown that at a given tongue length the force generated owing to the membrane deformation and acting to redistribute the spectrin, overcomes (in some membrane area) the association force density and results in an additional increase of the sucked membrane length. Equations have been derived to describe this process. From the experimental conditions of an RBC aspiration and the determined tongue length corresponding to the second slow aspiration step, the association force density between the lipid bilayer and the spectrin network may be determined. From literature data and our own results a force density of between 40 and 50 Pa has been estimated.

Cytological Techniques↗
PubMed1991

Leakage of mechanical heart valve prostheses of Björk-Shiley type: in vitro investigations using Newtonian fluids.

The leakage of mechanical heart valve prostheses with tilting disc occluders was investigated. A U tube apparatus and a quasi-stationary method were used for measuring the backflow pressure characteristics. The method has several advantages over pulsatile or oscillatory techniques described in the literature. We have attempted to interpret the results of our measurements in terms of laminar and turbulent losses of energy. This leads to dimensionless loss numbers for valve leakage which are independent of arbitrary experimental conditions.

Biomechanical Phenomena↗
PubMed1991

Action of rHuEpo on mechanical membrane properties of red blood cells in children with end-stage renal disease.

By means of a micropipette aspiration technique mechanical membrane properties of RBC in ten uraemic children undergoing haemodialysis were compared to those of nine healthy children. In contrast to the healthy reference group (mu = 4.01 +/- 0.71 microN/m), the mean apparent elastic shear modulus of RBC membrane mu as a parameter of static deformability was significantly increased to 9.05 +/- 1.61 microN/m in children with chronic renal failure measured in the pre-study period. At the 7th week of the correction period of rHuEpo therapy, the haematocrit of treated patients is enhanced to a mean of 0.30 +/- 0.03, whereas mean mu is decreased to 5.41 +/- 0.63 microN/m. Within the maintenance period of rHuEpo treatment (30th week), the parameter mu did not show significant differences to the reference value 3.78 +/- 0.31 microN/m. Additionally, a significant increase in red cell mean corpuscular volume was obtained during rHuEpo therapy. Improved deformability of uraemic RBC induced by the rHuEpo therapy can only be explained by the assumption that in the course of this therapy an increasing number of cells with normalised viscoelastic properties have been formed by stimulated erythropoiesis.

Adolescent↗
PubMed1991

[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.

Blood Flow Velocity↗
PubMed1991

Influence of white blood cells on the filterability of human erythrocytes: modelling of the filtration process and experimental results.

In medical research and clinical practice, the increasing application of filtration measurements, to characterize the erythrocyte deformability has aroused an intensive discussion about possible erroneous interpretations of measured values (filterability indices). In the present paper the influence of white blood cells (WBC) on these indices is described and discussed in relation to a mathematical model of the filtration process. We found for two gravity filtration systems, using cellulose filters and concentrated erythrocytes suspensions sensitivities of their filterability indices of (1 +/- 0.1)% per 100 WBC/microliter (initial filtration rate measurement) and (3 +/- 0.3)% per 100 WBC/microliter (hemofiltrometer). In comparison to Nuclepore filtration systems with sensitivities of 5-12% per 100 WBC/microliters, cellulose filters were much less sensitive to WBC. The necessity, advantages and disadvantages of additional procedures for WBC removal are discussed. A standardization of residual WBC-count in limits of 500 +/- 300 WBC/microliters at a hematocrit of 60% is proposed. Fitting of the filtration curves of the hemofiltrometer to a model function may either improve the accuracy of estimation of filterability indices or divide them into two model parameters with different WBC-sensitivities: the initial filtration rate parameter having a low WBC-sensitivity ((0.9 +/- 0.2)% per 100 WBC/microliter) and the occlusion related parameter having a 12 times higher sensitivity ((11 +/- 1)% per 100 WBC/microliter). Interpretation, advantages and disadvantages of the model parameters are discussed also in comparison to the filterability index.

Cellulose↗
PubMed1991

Changes in rheology and red blood cell function under recombinant human erythropoietin therapy.

The rh-EPO is a potent drug to treat renal anaemia. RBC aggregation is not influenced by the rh-EPO therapy. Membrane elasticity and RBC deformability improve remarkably after rh-EPO which might benefit microcirculation. Rh-EPO therapy can not prolong RBC life span. Obviously uremic milieu alone determines RBC life time. Rh-EPO treatment corrects renal anemia by increasing the number of RBC and the RBC volume.

Adult↗
PubMed1991

Elastic properties of passive leukemic white blood cells.

The key role of leukocytes (WBC) in pathologic alterations of microcirculation was repeatedly described in the literature. The aim of this study was to compare the mechanical characteristics of WBC of 4 healthy donors and 6 patients suffering from chronic myeloid leukemia (CML). The elastic properties of individual leukocytes in the passive state were studied by the micropipette technique (aspirating pressure delta P = 100 divided by 250 Pa; internal pipette radius Rp = 1.4 divided by 2.6 microns). The passive elastic rigidity of WBC (PER) from 30 cells/donor was characterized by the amplitude of their steady-state deformation (Dp) normalized for the pipette radius (Rp) against the stress parameter delta P * Rp. The effect of a CML-therapy with cytostatics was monitored by way of differential blood counts. A significantly higher rigidity of healthy lymphocytes (PER = 349.7 +/- 125.9 microN/m; n = 45) than that of polymorphonuclear granulocytes (PER = 226.5 +/- 86.7 microN/m; n = 62) was seen which appears to result from their large, solid nucleus. Control leukocytes have a significantly higher rigidity than leukemic WBC. Leukemic granulocytes (PER = 155.1 +/- 67.7 microN/m; n = 61) and lymphocytes (PER = 134.3 +/- 51.9 microN/m; n = 62) do not differ significantly in their values of rigidity.

Adult↗
PubMed1991

[Characterization of erythrocyte deformability by filtration technics. 5. The effect of leukocytes on the filterability of erythrocytes].

Filterability measurements have been used widely in medical research and clinical practice to characterize erythrocyte deformability. In the present paper the influence of white blood cells (WBC) on the of filterability indices is investigated and discussed. We found for two gravity filtration systems using cellulose filters and concentrated erythrocyte suspensions sensitivities of their filterability indices of 1% per 100 WBC/microliters (initial) filtration rate measurement) and 3% per 100 WBC/microliters (hemofiltrometer). The necessity, advantages and disadvantages of additional methods for WBC removal are discussed in comparison to nuclepore filtration systems with sensitivities of 5-12% per 100 WBC/microliters. The standardization of residual WBC-count in limits of 500 +/- 300 WBC/microliters at a hematocrit of 60% is proposed.

Erythrocyte Deformability↗
PubMed1990

Freshwater fish diet affects lipid composition, deformability and aggregation properties of erythrocytes.

The effect of a 12-week diet of freshwater fish on fatty acid composition of the erythrocyte membrane, RBC deformability and artificial aggregation behavior of erythrocytes was studied in 20 healthy subjects. A different quantity of meals containing fish per week (control group, 1.5 and 3.8 fish meals per week) resulted in an increased content of n - 3 polyunsaturated fatty acids. The whole cell deformability of single erythrocytes characterized by a modified micropipette technique (capillary-rigidometer) was significantly increased dependent on fish intake. The parameter of entry time for cell deformability had a negative correlation with the n - 3/n - 6 ratio of fatty acids. No change was observed in MCV and MCHC of erythrocytes after the diet. The artificial aggregation behavior of washed erythrocytes in a suspension medium of low ionic strength and reduced pH was decreased depending on the number of fish meals eaten. The present results suggest that a relatively small shift in the profile of the polyunsaturated fatty acids causes changes in the viscoelastic properties of the erythrocyte membrane and in the artificially-induced aggregation of erythrocytes.

Adolescent↗
PubMed1990

Theoretical model of blood flow through hollow fibres considering hematocrit-dependent, non-Newtonian blood properties.

Accounting for the non-Newtonian blood viscosity by the Quemada descriptive viscosity equation, we deduced velocity profiles and volumetric capillary flows from the Navier-Stokes-equation. An arbitrary axial and/or radial hematocrit profile can be chosen. The hematocrit dependence of the intrinsic viscosities k0 (H) (characterizing, at least in part, the RBC aggregation) and k infinity (H) (describing orientation/deformation of RBC) was taken into account. Velocity profiles for pressure gradients of 4-4000 Pa/cm show a distinct flattening, if a pronounced axial migration of RBC is assumed. The higher the axial concentration, the higher the flow at the same pressure gradient. Small deviations (less than or equal to 10%) of the capillary number per dialyzer or of the radius of capillaries lead to a strong change of the pressure gradient with the same dialyzer flow. Whereas small hydraulic conductivities do not significantly change this gradient, high conductivities decrease the pressure gradient by about 10%. Impaired blood flow properties (hemoconcentration) result in a slight deviation from the linear axial pressure drop.

Blood Flow Velocity↗
PubMed1989

[The flow properties of blood and their characterization by hemorheologic methods].

In a number of supply disturbances the flow behaviour of blood plays an increasing role in modern therapy concepts. The present paper deals with representing factors, such as haematocrit, aggregation, deformation, which exercise an influence on the complex flow properties of blood under variable conditions. By referring to the example of deformability it is shown how and to what extent different mechanical parameters of individual erythrocytes participate in static or dynamic whole cell deformation. Starting from fundamental quality demands (sensitivity, specificity, value of prediction) to diagnostic measuring technique, haemorheological methods for determining complex flow properties, aggregation and deformation as single phenomena and mechanical properties of individual erythrocytes are presented. Selected examples of application for normal blood, cells altered in vitro or pathological changes measured ex vivo are referred to.

Blood Flow Velocity↗
PubMed1989

The effect of rimantadine on the structure of model and biological membranes.

The action of the antiviral drug rimantadine on the structure of bilayer lipid membranes (BLM) and RBC membranes was investigated. Structural changes in BLM were recorded by ionophore conductivity changes and by changes in the third harmonic of capacity current signal due to lateral compression of BLM in an electric field. It was shown that the adsorption of rimantadine on BLM results in an increase in ionophore mobility in bilayer membranes of dioleolyllecithin (DOL) and common lipids of bovine brain (CL) and in a decrease in those of azolectin (A). Relative changes in the third harmonic signal also depend on the membrane composition and have different signs. The results may be explained by the rimantadine action on the lipid bilayer structure: "rigidification" of A-membranes and "fluidization" of BLM from DOL and CL. Structural reorganization of RBC membranes as investigated by the ability of the cells to enter a micropipette (inner diameter greater than or equal to 3 microns) thereby undergoing deformation. It was shown that rimantadine influences RBC deformability due to drug induced inhomogenous mechanical membrane properties. Also, rimantadine accelerated the process of artificially induced aggregation of erythrocytes. The relation of the effects on artificial and biological membranes, and the structural changes in the lipid phase of membrane are discussed.

Adamantane↗
PubMed1988

Separation of red blood cells at high volume concentration under low centrifugal accelerations.

The separation process of blood and RBC suspensions in a hematocrit range between 0.3-0.7 was investigated with a centrifuge allowed to run at low accelerations (100 xg-1000 xg). The position of the interface between the supernatant of plasma and the RBC column was continuously recorded by a new optoelectronic measuring system. The separation process could be mathematically described by an exponential decrease of the cell column approaching a final packing. At a given centrifugal acceleration the time constant is influenced by hematocrit, aggregation, deformation and plasma viscosity. The final packing depends linearly on the starting hematocrit (0.3-0.7) and can be used as a measure of deformability.

Blood Sedimentation↗
PubMed1988

RBC membrane instability for large pipette deformation. A theoretical approach.

Under conditions of high pressure difference micropipette aspiration experiments show a "pinch-off" phenomenon as observed by RAND /31/. In a very recent paper, MEIER et. al /9/ have reported about new data obtained with a modern electronic technique under moderate mechanical load. We have theoretically analysed the conditions necessary to form such a instability. In our approximations we have investigated the effective transmembrane pressure difference which is given both by the true pressure drop, determined by the hydrodynamic flow through a small gap between the cell tongue and the pipette wall and the interaction between the tongue and the wall, as well as by the nonisotropic part of the membrane tension. When the membrane tongue is long enough (greater than 3Rp) we have found a condition for the loss of membrane stability in a point where a minimum of the effective transmembrane pressure drop occurs. An expression for it and the vesicle size are given.

Animals↗