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Biomedical subjects

J F Stoltz

Publications and source records attributed to J F Stoltz.

At least 55 records · Page 3Linked to original sources
PubMed2000

Atrial heart fibrillation modeling: a tool for adequate choice of signal processing functions.

Framingham Study showed that Atrial Fibrillation (AF) exposes the patient to an increased stroke risk and to low cardiac output. It is well known that the mechanism of Atrial Fibrillation is reentry. In order to facilitate AF's studies, we propose a deterministic model that can be used for cardiac signal characterization. The model is based on a linear combination of several "Atrial Flutter-like signals. We obtained AF-close aspects. To demonstrate its usefulness we performed a power spectrum transform (i.e. scalar Fast Fourier Transform) of this model. Thanks to the model we show that this transform cannot be used as is, and may induce errors in results interpretation. We also show based on the same example how to overcome the limitation with help of the model. We expect that this model will help in mathematical transforms relevance evaluation. This may lead to new findings in AF classification, and to improvement in patients' treatment, follow-up and survival.

Atrial Fibrillation↗
PubMed2000

Osmotic fragility of the erythrocyte membrane: characterization by modeling of the transmittance curve as a function of the NaCl concentration.

The theoretical extinction of blood suspensions submitted to a slow dialysis is analyzed in terms of their NaCl concentration. The model involves two adjustable parameters, chi and K, related to swelling and hemolysis. During swelling, the erythrocyte volume is supposed to vary linearly with the saline concentration. During hemolysis, an exponential decay of the hemoglobin concentration in the erythrocyte is used. The theoretical transmittance curves are consistent with the measurements carried out at a wavelength of 0.808 microm on native and incubated blood samples. Chi and K are relevant parameters to characterize quantitatively the fragility of the erythrocyte membrane. The effect of a non ideal character of the hemoglobin solutions and of normal distributions of chi and K is also discussed.

Dose-Response Relationship, Drug↗
PubMed2000

Regulation of von willebrand factor of human endothelial cells exposed to laminar flows: an in vitro study.

The effect of laminar flow on the regulation of von Willebrand Factor (vWF) of cultured human umbilical vein endothelial cells (HUVECs) was studied. Confluent endothelial monolayers were exposed to shear stresses (0.2 and 1.0 Pa) from 2 to 24 h. vWF was labelled with indirect immunofluorescence method and observed with 3D fluorescence microscopy. The distribution of vWF and the cytoskeleton organization were observed simultaneously by double fluorescence labelling. More actin stress fibers and an increased release of vWF appeared in the cells exposed to flow at the same time. The qualitative and quantitative results showed that there was not only a shear-dependent regulation but also a time-dependent modification. For a short-time shear stimulation, both 0.2 Pa and 1.0 Pa shear stresses induced a release of vWF from the endothelial cells. In contrast, after 24 h exposure to 1.0 Pa shear flow, vWFs were much more in the cells than that in the cells exposed to 0.2 Pa for 24 h (p < 0.01) or that in the control cells (p < 0.05). TNF-alpha caused a decrease of vWF and Weibel-Palade bodies in the cells.

Actin Cytoskeleton↗
PubMed2000

Validation of a test of the red cell membrane osmotic resistance.

The aim of the present work was to validate a new technique for the measurement of resistance of the red blood cell membrane using an automated apparatus called a Fragilimeter. Its principle lies in the measurement of the extinction of a laser beam projected through a red blood cell suspension subjected, by diffusion, to a variation of salinity from an isotonic equilibrium (154 mM NaCl) to, a hypotonic one, 25 mM NaCl. The variation of osmotic pressure induces on the cells a progressive lysis and a modification of the extinction of the transmitted light. The validation of the method was based on the comparison between results obtained with the Fragilimeter and those obtained using the reference DACIE technique. Analyses were based on blood samples from healthy donors. The determination of the initial, the 50% and the full haemolysis thresholds allowed observation of the fragility of the cell, through its membrane resistance. The physical phenomenon measured in these cells when subjected to various ionic strengths is discussed on the basis of observations realised by means of an optical microscope.

Electronic Data Processing↗
PubMed2000

Tetramethylpyrazine inhibits phytohemagglutinin-induced upregulation of ICAM-1 and LFA-1 mediated leukocyte adhesion.

The aim of this work was to study the effects of tetramethylpyrazine (TMP) on the interaction between lymphocyte function-associated antigen-1 (LFA-1) and intercellular adhesive molecule-1 (ICAM-1) by micropipette technique. A pair of cells, i.e., a human lymphocyte or a S KW-3 cell (human T cell leukemia), LFA-1 was expressed on which cellular surfaces, and a RBC coupled with ICAM-1, were the carriers for LFA-1 and ICAM-1. The adhesion probabilities of this pair of cells were mediated by specific interactions between ICAM-1 and LFA-1. Phytohemagglutinin (PHA) stimulation resulted in the significant increase in the adhesion probability compared to the resting lymphocyte. TMP treatment can inhibit such increase and even make the adhesion probability lower than the resting state. While the LFA-1 expression has not changed significantly with PHA stimulation or with TMP treatment, which indicated that TMP inhibiting effects was realized by a possible conformation change.

Adult↗
PubMed1999

Rheological behaviour of red blood cells suspended in hemoglobin solutions. In vitro study comparing dextran-benzene-tetra-carboxylate hemoglobin, stroma free hemoglobin and plasma expanders.

Circulating volume expansion for intentional hemodilution and/or resuscitation of hemorrhagic shock can be performed with hemoglobin-based oxygen carriers (HBOC) which, in addition to oxygen transport, have vasoactive effects through poorly documented mechanisms. Among these, the effects of HBOC on red blood cell (RBC) rheology are relatively unknown. The aim of the present in vitro study was to measure the rheological effects of human hemoglobin bound to benzene-tetracarboxylate substituted dextran (Dex-BTC-Hb) as an example of chemically modified hemoglobin. The viscosity was assessed with a capillary and a rotational viscometer for shear rates of 0.5-128 s-1. Erythrocyte aggregation was determined by analysis of the red light backscattered in a RBC suspension and with a rheoscope. The deformability was determined by the pressure-flow relationship of the RBC suspensions passed through polycarbonate filters. At hematocrit of 0.35 l/l and at low shear rates, the viscosity of RBC was higher in the presence of Dex-BTC-Hb as compared to free Hb, Dex-BTC, Dextran 40 (Plasmacair), modified fluid gelatin (MFG-Plasmion) or hydroxyethyl starch (HEA-Elohes). The effect on erythrocyte aggregation of Dex-BTC-Hb was greater than that of standard solutions, but close to that of MFG or HEA. There was no apparent change in RBC deformability. Dex-BTC-Hb, unlike free Hb, has a hyperaggregating effect on RBC, similar to that of some clinically used volume expanders. This hyperaggregating effect could influence the in vivo rheological behavior of substituted Hb by increasing shear stress.

Blood Substitutes↗
PubMed1999

[Vascular disease and cellular activation: exploration of cell adhesion phenotype by quantitative flow cytometry].

The pathogenesis of atheromatous and/or thrombotic vascular diseases involves rheological parameters, soluble mediators and cellular agents. The many studies that have tried to establish correlations between plasma factors, shear stress and the risk of ischemia have left some questions unanswered. Current exploration methods are now focusing on the determining role of cells. Activated cells express adhesion molecules on their membranes, which allow to communicate in a homo- or heterotypical manner. Quantifying adherence molecules on the surface of platelets, leukocytes and endothelial cells provides an assessment of the "adhesive phenotypical profile". Quantitative cytometry, using beads coated with a known amount of immunoglobulins as calibrators, is perfectly suited, through its multiple parameter analyses and the specificity provided by monoclonal antibodies, for the quantification of membrane antigens. Measuring the adhesive profile on the surface of cells that are implicated in vascular disease makes it possible to correlate that phenotype to the ischemic risk in such diversified pathologies or circumstances as intermittent angor, myocardial infarction, angioplasty, insulin-dependent diabetes or pre-eclampsia. In addition, that quantification permits monitoring the action of new therapeutical agents targeting adherence molecules.

Angioplasty, Balloon, Coronary↗
PubMed1999

Senescent erythrocytes: modification of rheologic properties, antigenic expression and interaction with monocytes.

Human erythrocytes have a well-defined lifespan of 120 days. Their eventual removal from circulation is a complex process affected by many cellular parameters, making them susceptible to sequestration in the spleen and other organs. The purpose of this study was to investigate putative changes in rheologic properties, antigenic expression and interaction with monocytes of senescent erythrocytes (SE). SE and young erythrocyte (YE) fractions were obtained by differential centrifugation from 20 healthy donor blood samples. Membrane rheomechanic properties (by diffractometric method), ABO and MN antigens reactivity and erythrophagocytosis by peripheral monocytes were investigated in each fractions. SE showed a little decrease in the deformability index and an increase of both membrane elastic modulus and surface viscosity. The studies performed indicate a decreased expression in the antigens of both blood group systems studied (p < 0.01) and an increased rate of erythrophagocytosis by monocytes in SE compared to YE (p < 0.01). The significant modifications in the biomechanic properties of senescent red blood cell membrane and the loss of antigenic expression could lead to physiological phagocytosis.

Antigens↗
PubMed1999

[Hemorheology and vascular endothelial cells].

The vascular endothelium is a biologically active monolayer of cells providing an interface between the blood flow and tissues. Vascular Endothelial Cells (VEC) have two functional states. The endothelium is normally anti-thrombotic and anti-adhesive to ensure blood fluidity. During aggressions, such as atherosclerosis, inflammation states, metabolic diseases (through chemical or mechanical stimuli), VEC can reverse its functions by expressing stored material or by slower involvement of previously are repressed genes. Endothelial cells have three types of anti-thrombotic properties: vaso regulating properties: VEC release vasomotor components, such as endothelin (vasoconstriction), prostacyclin and nitric oxide, (vasodilatation). Endothelial cells also have antithrombotic and hemostatic properties. They express proteoglycans on their surface, including some negative-charge, plasminogen, sulfate glycosaminoglycans (heparan-sulfate), and secrete plasminogen tissular activator (t-PA) and tissular factor inhibitor. One fundamental action of the endothelium in that area is the production and expression of thrombomodulin, a thrombin receptor. This function has a major anticoagulation effect, controlling continual thrombin generation at the sub-endothelium and blood cell interface. Moreover, endothelial cells show anti-adhesion properties. During cardio-vascular diseases, all of these properties may be reversed. Thus the VEC have a determinant role in hemodynamic control through these various metabolic activities, such as control of homeostasis, vascular tone, blood fluidity, coagulating properties, cellular adhesion. Otherwise, many studies have demonstrated that local blood flow conditions have a crucial role on the VEC properties (mechanoactivation and mechanotransduction concept). In conclusion, knowledge of all the properties of the endothelial cells and control of the phenomena which define their functions is a key element in understanding cardiovascular diseases.

Animals↗
PubMed1999

Hemorheology and vascular endothelial cells.

The vascular endothelium is a biologically active monolayer of cells provided an interface between blood and tissues. Vascular endothelial cells (ECs) have two functional states, which are allowed by their different properties: (i) vaso regulating properties: ECs releases vasomotor components, as endothelin (vaso constriction), prostacyclin and nitrite oxide (vaso dilatation); (ii) antithrombotic and hemostatic properties; and (iii) anti-adhesion properties. The endothelium is normally antithrombotic and anti-adhesive to ensure blood fluidity. During many cardio-vascular diseases, these properties may be reversed. Thus, the ECs have a determinant role in hemodynamic control through these various metabolic activities. Otherwise, many studies have demonstrated that local blood flow conditions have a crucial role on the EC properties (mechanotransduction concept). The knowledge of the properties of ECs and the control of the phenomena which define their functions is a key element in the cardiovascular diseases understanding.

Animals↗
PubMed1999

Elasticity and fracture strain of whole blood clots.

The measurement of clot elasticity and fracture strain is carried out using a rotational rheometer with a controlled stress system. The elasticity is quantified by a shear elastic modulus and fracture strain by a critical strain (deformation) when the clot begins to break up. The results indicate a decrease of elasticity and increase of fracture strain of the clot with increasing hematocrit. Moreover, the elastic modulus of the clot is not constant but increasing with deformation.

Blood Coagulation↗
PubMed1999

Development and evaluation of an automatic method for the study of platelet osmotic response.

Study of the osmotic resistance to hypotonic medium of platelets has often been suggested as a global test to assess the viability of these cells in transfusion or to study modification during haematological pathologies. A number of authors have analysed the behaviour of platelets in hypotonic media by a variety of methods (cell count, determinations of substances released, morphology, etc.), but most studies are currently based on the so-called "Hypotonic Shock Response" test (HSR). In this study, the authors describe a new automated and reproducible apparatus, called fragilimeter, using slow dialysis to assess platelet osmotic resistance. The variations in light transmission through a platelet suspension according to ionic strength are linked to the change in cellular volume and lysis and characterise the osmotic behaviour of the cells. The results revealed the good reproducibility and sensibility of the technique. This apparatus allows also the realisation of the "HSR" test.

Adult↗
PubMed1999

Influence of a calcium antagonist on blood rheology and arterial compliance in hypertension: comparison with a thiazide diuretic.

Beyond their effects on blood pressure, antihypertensive agents may produce additional effects on blood rheology and arterial compliance abnormalities which may play a role in the target organ damage. These effects may depend only on their specific pharmacological properties. We compared the effects of nitrendipine to hydrochlorothiazide in 33 mild to moderate hypertensives in a double blind parallel group trial. Blood rheology and radial artery diameter and compliance were measured at t=0 and t=2 months. Both drugs produced blood pressure lowering. Blood viscosity decreased in the nitrendipine group and increased in the hydrochlorothiazide patients. Red blood cells deformability increased only in the nitrendipine group. Radial artery diameter and compliance were not different between the two groups but there was a trend to an increase of the cross-sectional compliance in hydrochlorothiazide group and to a decrease in nitrendipine group. Our data show that a calcium antagonist (Nitrendipine) could improve rheological parameters.

Antihypertensive Agents↗
PubMed1999

Membrane fluidity and oxygen diffusion in cholesterol-enriched endothelial cells.

In this study, we measured the influence of cholesterol rigidification on oxygen permeability in human endothelial cell monolayer membranes (ECs). Cholesterol-induced membrane rigidification was assessed at different membrane depths by a fluorescence polarization method with diphenyl-hexatriene (DPH) and 1-(4-trimethylamino)-6-phenylhexatriene (TMA-DPH). Fluorescence quenching by oxygen was probed in preferentially labelled membrane with pyrene butyric acid (PyC4) and pyrene dodecanoic acid (PyC12), as shown with a 3D fluorescence microscope (CellScan System). With both probes the experiments revealed a decrease in oxygen diffusion as the cholesterol concentration increased in the medium culture (from 3.42 microM to 17.11 microM). We showed that very low concentrations of cholesterol (about 1000 times below normal value, 6.2 mM) particularly decrease oxygen levels or diffusion rate in the middle region of the membrane. In conclusion, these findings prove in a direct manner that cholesterol significantly affect the endothelial barrier function and molecular oxygen transfer to underlying tissues. Risk factors (cholesterol) directly would contribute to tissue ischemia.

Biological Transport↗
PubMed1999

Measurement of erythrocyte deformability by two laser diffraction methods.

The aim of this work is to study the deformability of red blood cells (RBC) by two laser diffraction methods: the Laser-assisted Optical Rotational Cell Analyser (LORCA, Mechatronics, Amsterdam, Netherlands) and a Shear Stress Diffractometer (RHEODYN SSD, Myrenne, Roetgen, Germany). Experiments were carried out on 46 healthy human subjects. The elongation index EI of normal and hardened RBCs (obtained by heating blood at 49 degrees C or by incubating RBCs in solutions of diamide) was measured. The results showed that the standard deviations of the experimental data for normal RBCs were relatively small, especially at high shear stresses (more than 3.0 Pa), but higher than those reported before. Some correlations between the results given by the two instruments were also found. It should be noted that for hardened RBCs, the standard deviations of the measurements were important compared with the mean values in the two instruments.

Adult↗
PubMed1999

Comparison of three optical methods to study erythrocyte aggregation.

The aim of this work was to evaluate three optical methods designed to determine erythrocyte aggregation: Erythroaggregometer (EA; Regulest, France), Laser-assisted Optical Rotational Cell Analyzer (LORCA; Mechatronics, Netherlands) and Fully Automatic Erythrocyte Aggregometer (FAEA; Myrenne, GmbH, Germany). Blood samples were taken from fifty donors (26 males and 24 females). The aggregation of normal red blood cell (RBC) and RBCs suspended in three normo- and hyperaggregating suspending media was studied. The results revealed some significant correlations between parameters measured by these instruments, in particular, between the indexes of aggregation of EA and LORCA. Further, RBC aggregation of multiple myeloma patients was also studied and a hyper erythrocyte aggregation state was found by EA and LORCA.

Adult↗