Biomedical subjects

J C Lelievre

Publications and source records attributed to J C Lelievre.

14 recordsLinked to original sources

PubMed1994

Effects of two low-osmolar contrast media, ioxaglate and iopamidol, on erythrocyte membrane elasticity.

RATIONALE AND OBJECTIVES: The effect of ioxaglate and iopamidol, two recently developed low-osmolality contrast media, on the shear elasticity of erythrocyte membranes was studied at an iodine concentration of 300 mg/mL and at a 20% volume concentration and compared with that obtained for control solutions matched in osmolality. METHODS: The authors used a micromanipulation technique, which consists of visualizing deformations of individual erythrocytes when gently aspirated into the tip of a glass micropipette by an accurately controlled pressure. An erythrocyte membrane shear elasticity modulus mu was then deduced. An increase in mu corresponded to an increase in erythrocyte membrane rigidity. RESULTS: In all cases, the erythrocytes remained discocytic. The shear elasticity modulus of the erythrocyte membrane is found to be (1) in the presence of ioxaglate (4.3 +/- 0.9 microN/m) lower (P < .001) than in the presence of hyperosmolar saline (6.2 +/- 1.3 microN/m) and lower (P < .02) than in the presence of iso-osmolar control (4.7 +/- 0.7 microN/m); (2) in the presence of iopamidol (5.4 +/- 0.7 microN/m) lower (P < .001) than in the presence of hyperosmolar sucrose (6.4 +/- 1.2 microN/m) and higher (P < .001) than in the presence of iso-osmolar control (4.7 +/- 0.7 microN/m); and (3) lower (P < .001) in the presence of ioxaglate (4.3 +/- 0.9 microN/m) than in the presence of iopamidol (5.4 +/- 0.7 microN/m). CONCLUSIONS: Under the experimental conditions used, both contrast media (ioxaglate and iopamidol) modify the erythrocyte membrane shear elasticity modulus less than do the matched hyperosmolar controls. Moreover, ioxaglate makes the erythrocyte membrane less rigid, and iopamidol makes the erythrocyte membrane more rigid than does the iso-osmolar control.

Elasticity↗

PubMed1992

[Raynaud's phenomenon and blood viscosity].

Raynaud's phenomenon is mainly linked with cold provoked vasomotor perturbations, but also with rheological alterations since blood viscosity is enhanced by lowering temperature. Several methods are available for studying distal vascularization: peri-ungual capillaroscopy, digital plethysmography and laser-Doppler. Digital arteriography must be reserved to serious ischemia regarding the general anesthesia needed to avoid spasm. All these methods explore especially the vessel wall. Conservely, blood viscosity which has been developed for 25 years investigates the content of the vessel. Since 1965, numerous hemorheological studies pointed out the rheological disorders, especially those concerning plasma and blood viscosity. The most usual viscometry abnormalities revealed erythrocyte hyperaggregation, red cell hypodeformability, blood and plasmatic hyperviscosity. In a comparative study, 46 patients with Raynaud's phenomenon were studied: we performed peri-ungual capillaroscopy, plethysmography and viscosity measurements. The results demonstrated a link between capillaroscopy and thixotropy. Both investigations are never normal at the same time in connectivites and never abnormal at the same time in Raynaud's disease (primary Raynaud's phenomenon). In conclusion hemorheological studies showed nearly normal rheological parameters in Raynaud's disease, but abnormal rheological parameters in secondary Raynaud's phenomenon.

Adult↗

PubMed1991

[Hemorheologic effects following ergometric-controlled physical exercise].

In collaboration with the Laboratory of Physiology, the Unity of Biorheology realized hemorheological studies on healthy volunteers who performed four kinds of well-controlled exercises on a cycle ergometer. Blood was always collected just before exercise and just after exercise. Rheological measurements were performed (blood and plasma viscosities, blood thixotropy and blood viscoelasticity) as well as biological (plasma proteins) and biophysical (osmolarity, pH) measurements. In all the cases, results show the importance of a hemoconcentration and its hemorheology consequences.

Blood Viscosity↗

PubMed1990

Determination of the red blood cell apparent membrane elastic modulus from viscometric measurements.

Rhelogical measurements on a dilute suspension of red blood cells (RBCs) are interpreted by means of a microheological model that relates the shear evolution of the apparent viscosity to the intrinsic properties of the suspended particles. It is then possible to quantify the average deformability of a RBC population in terms of a mean value of the membrane shear elastic modulus, Es. Dilute suspensions of erthrocytes exhibit shear-thinning behavior with a constant high shear viscosity. This behavior is identical to the one predicted for a suspension of spherical capsules where the same phenomena of deformation and orientation prevail. A comparison between theoretical and experimental curves yields a mean value of Es, assuming all other cell properties--internal viscosity, geometry--to be otherwise equal. In Dextran, the values of Es for normal RBCs are found to be of order 3.10(-6) N/m. For erythrocytes hardened by heat exposure for 15 minutes at 48 degrees C, the increase in Es reaches 45 percent. This procedure of shear elastic modulus determination is easy to perform and seems to give a good discrimination between normal and altered erythrocytes.

Biomechanical Phenomena↗

PubMed1990

Size determination of red blood cell aggregates induced by dextran using ultrasound backscattering phenomenon.

Different methods are commonly used to study the red blood cell aggregation phenomenon. The major interest of the ultrasonic method presently discussed is to assess the mean size of red blood cell (RBC) aggregates by measuring ultrasonic intensity backscattered by blood. Applying Rayleigh theory of sound to blood medium, one can show that the scattered ultrasonic intensity is proportional to the 6th power of the size of the RBC aggregates. The ultrasonic method is used to evaluate the mean size of RBC aggregates induced by dextrans. RBCs are suspended at various hematocrits H, in solution of dextrans of different molecular weights M and at different weight concentrations Cw. Results are presented by using the ultrasonic backscattering coefficient chi which is a relevant quantity in a scattering experiment. For suspensions of RBCs aggregated with dextran of molecular weight 70,000 dalton (dextran 70) at concentration Cw = 40 g/l, variations of chi as a function of H are similar to those obtained for normal blood. At a fixed hematocrit, variation of chi versus Cw for dextran 70 exhibits a maximum at 40 g/l. In the case of RBCs suspended at hematocrit 20% and aggregated with dextrans of molecular weight M, 70,000 less than or equal to M less than or equal to 2,000,000, the variations of chi versus molar concentration Cm are similar to those of the microscopic aggregation index defined by Chien (1). Finally, a statistical model of the blood structure previously described (2) is applied to evaluate the mean size of the aggregates. According to this model, the mean size of aggregates is independent of hematocrit for H less than or equal to 40% and independent of the molecular weight of dextran for M greater than or equal to 150,000 dalton.

Dextrans↗

PubMed1988

Competitive role between fibrinogen and albumin on thixotropy of red cell suspensions.

Plasmatic proteins, namely fibrinogen and globulins, play a major role in red blood cell (RBC) aggregation which is accountable for the three-dimensional structure of blood. Consequently, blood rheological properties linked to this structure must be modified when the protein plasma content changes. This paper gives results and related comments on thixotropic properties of RBC suspensions (0.45 hematocrit) in isotonic solutions containing various amount of fibrinogen to which albumin is added. Thixotropic behavior of these RBC suspensions is studied with a low inertia coaxial cylinders viscometer at a shear rate step of Y = 1 s-1. Rheograms are interpreted in term of thixotropy coefficient. The main conclusion is that albumin improves RBC disaggregability of whole blood, resulting probably from a competitive effect between fibrinogen and albumin in the RBC aggregation process.

Blood Viscosity↗

PubMed1988

Determination of erythrocyte transit times through micropores. I--Basic operational principles.

To study the transit times of each red blood cell passing through cylindrical micropores and in order to evaluate sub-population of cells with regard to their deformability, we have developed a new system called the cell transit time analyser (CTTA). By using an AC voltage (100 KHz) across a special filter, we measure the electrical conductance change produced by the cells passing through the pores under a known driving pressure. This computer based device provides the distribution of transit times tau for 2000 cells in 1 minute and as a result the mean transit time [tau]. Experiments with red cells were designed to evaluate the flow behavior of both normal cells and cells whose mechanical properties were artificially altered. Cell volume was changed by use of non-isotonic media. Cell shape and cell volume were modified by varying the pH of the suspending buffer. Results of these experiments are: 1) a skew distribution of transit times towards high tau values for both control cells and artificially altered cells is observed: 2) [tau] is minimum for isotonic conditions and increases sharply for either hypotonic or hypertonic media: 3) [tau] is minimum at physiological pH and increases for either acid or alcaline changes of pH.

Blood Flow Velocity↗

PubMed1987

Tangent simple systems method applied to a precise study of viscoelastic behaviour of human blood.

The tangent simple systems (TSS) method, proposed in (1), is applied in order to study the viscoelastic behaviour of human blood in transient flow for a rectangular low shear rate step. The tangent simple systems which were used are Maxwell liquids. These systems allow one to obtain plots of variations of instantaneous values of viscosity coefficient mu, elasticity modulus G and retardation time tau = mu/G of the studied blood samples, as a function of flow duration. Variations of both parameters mu and G versus time are represented by two exponential functions which involve three couples of parameters (mu o, mu infinity), (Go, G infinity) and (tau mu, tau G). These parameters can be considered as the characteristics of each blood sample. Another representation of the results, called the dual rheogram, is also indicated. The dual rheogram enables one to follow the evolution of the blood structure. Several examples of application of the TSS method to normal blood sample and to suspensions of artificially modified red blood cells (RBC) are given.

Blood Viscosity↗

PubMed1987

Aggregation of red blood cells studied by ultrasound backscattering.

The erythrocyte aggregation phenomenon is an important factor in capillary circulation. This phenomenon can be evaluated by a number of methods (microscopic observations, viscometry, light measurements) which cannot be applied simply to in vivo measurements. In contrast, ultrasound which propagates through soft tissues allows measurement of the mechanical properties of red blood cell (RBC) suspensions which depend on the aggregation phenomenon. We devised an apparatus in order to measure in vitro the ultrasonic backscattering intensity of RBC suspensions. First, with latex particles of different sizes, the ultrasonic backscattering coefficient has been measured in order to evaluate the apparatus response. Then, the ultrasonic backscattering coefficient of different aggregated erythrocyte suspensions has been measured and correlated with the erythrocyte sedimentation rate. Finally, the size of RBC aggregates of different suspensions has been evaluated.

Blood Sedimentation↗

PubMed1985

Quantitative characterization of blood rheological behavior in transient flow with a model including a structure parameter.

Transient rheological behavior of blood which involves non newtonian viscosity, elasticity and thixotropy can be modelized with a Maxwell rheological state equation which depends on a structure parameter having dimension of a shear rate. Identification of the model parameters leads to use an exponential apparent shear rate step and to use recursive filters for taking into account the impulse response of the viscometer servo-control device. Typical results for a normal blood sample are given.

Blood Physiological Phenomena↗

PubMed1983

Tentative application of the tangent simple system method to the study of the viscoelastic behaviour of blood.

The method of the tangent simple systems is applied to the study of the viscoelastic behaviour of human blood in unstationary flow for rectangular steps and triangular ramps of shear rate. The tangent systems we utilize, Maxwell liquids, enable us to determine, at every point of the rheograms, apparent instantaneous values of retardation or relaxation time, viscosity coefficient and elasticity modulus of the studied blood samples, and to plot the curves of variation of these parameters as a function of flow duration. A qualitative interpretation of the results is proposed from data on the aggregation-disaggregation kinetics of red blood cells. Examples are given for samples of normal and pathological bloods.

Biomechanical Phenomena↗

PubMedDate not supplied

Activity of Daflon 500 mg on the hemorheological disorders in diabetes.

A rheological study was performed on blood samples from 10 insulin-treated diabetics with retinopathy. As part of their treatment, they all received 4 tablets of Daflon 500 mg per day for 30 days. Three complementary rheological criteria were used to characterize blood samples: 1) viscometry, using a Couette viscometer, which produces data on viscosity, shear-thinning, viscoelasticity and tixotropy of blood, 2) aggregametry, using an apparatus based on light reflectometry, using a filtrometer based on the deformations red cells undergo as they pass through narrow pores which produces information on red cell deformability. The main results were: a better red blood cell disaggregability, a decrease in red blood cell aggregation and no change in red blood cell deformability.

Adult↗

PubMedDate not supplied

Hemorheological improvement after Daflon 500 mg treatment in diabetes.

Rheological disorders, such as blood hyperviscosity, red blood cell (RBC) hyperaggregation or hypodeformability, may be responsible for vascular complications in diabetes. As pointed out by many reports, flavonoids are known to act on RBC rheology in relation with venous thrombosis. These disorders were evaluated by viscometry in order to follow the hemorheological impact of a flavonoid (Daflon 500 mg). Hemorheological effects of Daflon 500 mg, 6 tablets per day for 28 days, were tested in 18 diabetic patients by viscometric measurements carried out on 2 ml blood sample withdrawn on EDTA. Measurements, before and after treatment, were compared with usual statistical tests. The following results were obtained: (1) a decrease of blood viscosity, more pronounced at low shear rate; (2) a better RBC disaggregability process under shear. Therefore, the main conclusion was that the hemorheological improvement, observed after Daflon 500 mg treatment, due to a decrease of RBC aggregation, can induce a decrease of blood flow resistance and a reduction in stasis and resulting ischemia.

Adult↗

PubMedDate not supplied

Viscous filtration of red blood cell suspensions.

Filtration experiments on red blood cell suspensions are usually conducted in a saline buffer solution. As a result, the flow of a particle in a pore is largely dominated by viscous effects, and it is not possible to distinguish between normal and membrane altered cells. A new approach to red cell filtration is proposed here, whereby the cells are suspended in a Dextran solution that has roughly the same viscosity as the internal hemoglobin solution. It is thus aimed to detect alterations of the membrane properties. In order to prove this point, filtration measurements are conducted with a hemorheometer on dilute (hematocrit 8%) suspensions of normal and membrane hardened (diamide treatment) cells, suspended either in a 8 mPa.s Dextran solution or in a 1 mPa.s buffer solution. As expected when the cells are suspended in buffer, there is no detectable difference in the filtration index for normal and treated cells. However, when they are suspended in the 8 mPa.s solution, the filtration index is significantly larger for treated than for normal cells. This shows that filtration in a viscous liquid can be used to measure changes in cell deformability due to membrane modifications.

Blood Viscosity↗