J. Dufaux

Bio: J. Dufaux is an academic researcher from University of Paris. The author has contributed to research in topics: Rouleaux & Biorheology. The author has an hindex of 2, co-authored 7 publications receiving 62 citations.

Etude de la cinétique d'agrégation érythrocytaire dans un écoulement de Couette

Abstract: 2014 Study of blood suspension aggregation in a Couette flow. Transmitted and backscattered light by blood suspension was theoretically studied, taking in account aggregation and orientation in a Couette flow. Theory can bring quantitative explanations of experimental data about laser light backscattered by blood suspension in a Couette flow. Relation between rouleaux size and the mean shear rate is proposed. Revue Phys. Appl. 15 (1980) ’l 357-1366 AOÛT 1980, Classification Physics Abstracts 46. 30R

[Characteristic transient times measured by backscattered laser light in blood suspension flow (author's transl)].

Abstract: An optical method is proposed for studying rouleaux formation and red blood cells (RBC) orientation. Both relations, first between m, the mean number of RBCs per rouleau and reflectivity, and second between the oriented RBCs fraction and the variation of the isotropic reflectivity are proposed. Our experimental data about aggregation relaxation time and orientation relaxation time are discussed and compared to viscometric results.

An Optical Method for Studying Red Blood Cells Orientation and Aggregation in a Couette Flow of Blood Suspension

Abstract: Red blood cell aggregation is certainly the most important factor in the non newtonian behaviour of normal human blood. Aggregated red blood cells build up rouleaux; this aggregation is reversible: at rest, the rouleaux form a three dimensional network structure; when a finite stress is applied to the suspension the structure breaks. Increasing the stress, the rouleaux are gradually disrupted and are finally reduced up to individual cells. With decrease in stress individual cells build up again rouleaux. In a steady state a dynamical equilibrium exists between the size of rouleaux and the stress applied. When the applied stress is high enough to break the rouleaux, cells can be oriented and deformed in the flow. There was studied an experimental method which allows us to rely the luminous flux backscattered by rouleaux and individual cells to their mean size and to their orientation.

Velocity Profile Measurements by Laser-Doppler Velocimetry (LDV) in Plane Capillaries. Comparison with Theoretical Profiles from a Two-Fluid Model

Abstract: Since the yeh and CUMMINS’ work 1 the velocity measurement of suspension flow with Laser Doppler Velocimeter has been widely developped. There are no important problems when the suspension concentration is low and when the tube dimensions are greater than those of the volume where the light beams interfere.

Optic nerve head blood flow using a laser Doppler velocimeter and haemorheology in primary open angle glaucoma and normal pressure glaucoma.

Abstract: Optic disc blood flow velocity was measured in healthy patients, those with primary open angle glaucoma (POAG), and patients with normal pressure glaucoma (NPG). The velocity of the red blood cells (RBCs) in the capillaries of the optic nerve head (ONH) has been measured with a laser Doppler velocimeter (LDV), and blood viscosity has been evaluated notably by determining the aggregability of the RBCs with an erythroaggregameter. Our results in POAG patients and NPG patients showed that their optic nerve blood flow velocity was reduced and that the aggregability of the RBCs was increased. The hyperaggregability of the erythrocytes is responsible for the increase of the local viscosity in the papillary capillary network. These haemodynamic modifications observed in patients with glaucoma support the hypothesis of a vasogenic mechanism that could impair the optic nerve in glaucoma patients.

Light-scattering technique for the study of orientation and deformation of red blood cells in a concentrated suspension

Abstract: The backscattered and transmitted diagrams of He–Ne laser light illuminating a concentrated suspension of red blood cells (RBC's) are investigated. The shapes of these diagrams are closely related to the state of the suspension (at rest or submitted to a simple shear flow) and to the parameters that govern the non-Newtonian behavior of the blood suspension (such as the viscosity of the suspending medium and the volume concentration of the cells). An asymmetry in the backscattering diagram, which is absent on transmitted diagrams, is observed when the suspension is in a simple shear flow. This asymmetry is related to the deformation and orientation of the RBC's. The propagation of light through the suspension is modeled and a set of Monte Carlo simulations is performed to substantiate the inference that the relative variation of the backscattered flux is proportional to the gradients of deformation of the RBC's, and that such gradients must be known in order to apply a rheological model describing the non-Newtonian behavior of RBC membranes.

The paradox of hematocrit in exercise physiology: which is the "normal" range from an hemorheologist's viewpoint?

Abstract: The paradox of hematocrit in exercise physiology is that artificially increasing it by autotransfusion or erythropoietin doping improves VO2 max and performance, while in normal conditions there is a strong negative correlation between hematocrit and fitness, due to a training-induced "autohemodilution". We aimed at investigating: (a) which is the physiological range of hematocrit in highly trained professional footballers; (b) what are the characteristics of athletes with high vs low hematocrit? We determined in 77 healthy male footballers the physiological range (mean +/- sd) of hematocrit: 42.3+/-2.74, (range -2sigma/+2sigma = 36.8-47.8%) thus defining boundaries of quintiles of distribution for this parameter: 40, 41.6, 42.9, 44.6. In another sample of 42 male footballers we compared three groups: lowest quintile (n = 8), highest quintile (n = 5) and the three middle quintiles considered together (n = 29). Athletes in the lowest quintile compared to those in the four other quintiles had a lower value of blood viscosity (-8%, p 44.6%) were frequently overtrained and/or iron-deficient, and their blood viscosity (and red cell disaggregability) tended to be increased.

Association between hemorheological alterations and metabolic syndrome.

Abstract: The contribution of hemorheological alterations in the prothrombotic condition in patients with metabolic syndrome (MS) remains a question of debate. We aimed to determine the association between MS and hemorheological parameters by means of a case-control study in 61 MS patients and 89 controls without MS. We determined blood viscosity at 230 s(-1) (Brookfield DVIII viscosimeter); plasma viscosity (Fresenius capillary plasma viscosimeter); erythrocyte aggregation at stasis and 3 s(-1) (MA-1 erythrocyte aggregometer); erythrocyte deformability (Rheodyn SSD at shear stresses of 12, 30 and 60 Pascals) and fibrinogen, along with anthropometric, lipidic and inflammatory parameters. MS patients showed increased blood viscosity (p = 0.018), plasma viscosity (p 8.23) and hyperfibrinogenemia (fibrinogen > 358 mg/dL) were independent predictors of MS: OR 3.34, 95% CI 1.40-7.93, p = 0.006 and OR 2.42 95% CI 1.04-5.66, p = 0.041, respectively. We conclude that MS is associated with an altered hemorheological profile related to inflammatory, lipidic and glucose intolerance parameters which could favor the development of thrombo-embolic and athero-thrombotic events in MS patients.

Increased red blood cell aggregation in retinal vein occlusion.

Abstract: Summary Reversible aggregation of red blood cells (RBC) plays an important role in determining the flow properties of blood, and is the cause of the increase in blood viscosity at low shear rates. Retinal venous circulation is characterized by the combination of a low flow state and a high vascular resistance which might severely limit its capacity to adjust to high blood viscosity. These characteristics make the venous circulation in the retina particularly dependent on haemorheological factors. To test the possibility that high RBC aggregation could predispose to the onset and development of retinal vein occlusion (RVO), RBC aggregation and disaggregation (SEFAM erythroaggregameter, France) were measured in 64 patients with RVO. Results were compared to those of a group of 64 controls, similar in age, sex, smoking habit and associated pathologies. Increased RBC aggregation was observed in 52% of the patients, and the mean values showed a highly significant elevation of RBC aggregation parameters in RVO patients (+ 14%) when compared with controls (P<0.001). Subgroups were compared to study the influence of site (central versus branch), form (ischaemic versus non-ischaemic), duration and severity of the occlusion on the aggregation parameters. No significant differences were found between these various subgroups. An increase in RBC aggregability and in the shear resistance of RBC aggregates, by predisposing to circulatory stasis, is likely to contribute to the onset of RVO.