Patrice Flaud - Academia.edu (original) (raw)
Papers by Patrice Flaud
ISRN Vascular Medicine, 2012
One particular characteristic of peripherally central catheter (PCC), peripherally inserted centr... more One particular characteristic of peripherally central catheter (PCC), peripherally inserted central catheter (PICC) or totally implantable venous access device (TIVAD), is to be submitted to a rotational movement around the shoulder in the daily routine. The aim of this paper is to show that these movements induce a variation of the inner volume of the catheter which may be responsible for an internal distal pollution of the lumen. The results are presented in the framework of an open discussion on the catheter protocols of use as well as a possible improvement of the materials.
La Houille Blanche, 2005
ABSTRACT Venous flow generates a large pressure gradient between lower limbs and the heart. In or... more ABSTRACT Venous flow generates a large pressure gradient between lower limbs and the heart. In order to correctly ensure blood circulation, several mechanisms coexist such as the plantar arch pump, the calf pump, breathing, walk accelerations and naturally, the heart action. These added mechanisms provide rapid variations of the wall vessels position and the fluctuations on the venous flow that have global effects on the circulatory flow. We developed a research program including an experimental set-up that could be numerically validated. Nevertheless, mechanical tube laws evaluation are image reconstruction dependent when tube collapses and it is thus necessary to compute areas precisely for a right validation of the tube dynamics. This communication introduces a new experimental set-up allowing strong vertical accelerations and also presents a new image reconstruction method to compute cross-section areas in collapsible tubes. Le débit veineux engendre un fort gradient de pression entre les membres inférieurs et le cœur. Afin d’assurer convenablement la circulation sanguine, différents mécanismes coexistent tels l’appui plantaire, la pompe du mollet, la respiration, les accélérations dues à la marche ainsi que l’action du cœur. Ces phénomènes conjoints induisent un déplacement rapide de la paroi des vaisseaux ainsi que des fluctuations de l’écoulement veineux ayant des effets globaux sur la circulation. Nous avons développé un programme de recherche incluant une partie expérimentale pouvant être validée numériquement. Les lois qui décrivent le comportement mécanique des tuyaux sont obtenues à l’aide de la reconstruction d’images lors du collabage du tube et impliquent un calcul précis sur les sections droites. Cette communication présente un nouveau dispositif expérimental acceptant de fortes accélérations verticales ainsi qu’une nouvelle méthode de reconstruction d’images permettant une mesure précise de l’aire de la section droite de tubes collabables.
La Houille Blanche, 2005
ABSTRACT During the pregnancy, the development and the fœtal growth depend on the placental vascu... more ABSTRACT During the pregnancy, the development and the fœtal growth depend on the placental vascularization by the maternal blood. The aim of this study is to achieve a better understanding of uteroplacental circulation physiopathology, the CFD enables us to reach information, usually inaccessible for ethical reasons or species specificity. We show a first simplified approach which proves the necessity of taking into consideration the blood rheological properties for the study of blood flows in the intervillous chamber. Tout au long de la grossesse, le développement et la croissance du fœtus dépendent de la vascularisation du placenta par le sang de la mère. L’objectif de ce travail est de permettre une meilleure compréhension de la physiopathologie de la circulation utéroplacentaire, l’outil numérique permettant d’atteindre des grandeurs habituellement non accessibles pour des raisons éthiques ou de spécificité d’espèce. On présente une première approche simplifiée qui démontre la nécessité de prendre en compte les propriétés rhéologiques du sang pour l'étude des écoulements sanguins dans la chambre intervilleuse.
AJR. American journal of roentgenology, 2014
![Research paper thumbnail of [Digital simulation of venous and lymphatic edema and the effects of compression]](https://attachments.academia-assets.com/45191839/thumbnails/1.jpg)
](Journal des maladies vasculaires, 2011
Compression therapy for venous and lymphatic edema of the lower limbs raises a major challenge co... more Compression therapy for venous and lymphatic edema of the lower limbs raises a major challenge concerning the optimal pressure ensuring both efficacy and patient compliance. We present a mathematical model of tissue fluid transfers which is aimed at determining the lowest pressure required to prevent edema. The model is based on a set of equations, derived from published experimental data, which describe the fluid and solute transfers between blood, interstitium and lymphatics, and the mechanical properties of interstitial compartment. It enables us to compute the changes in tissue volume, at the ankle level, resulting from increases of capillary pressure in case of venous insufficiency, and from an impairment of lymph drainage; as well as the effect of various external pressures upon this volume. An increase of capillary pressure to 40 and 50 mmHg results in an ankle edema which is completely prevented by an external pressure of 10 mmHg. This result is in keeping with the observati...
Journal of Hypertension, 1990
Since resistance to flow is theoretically determined by arteriolar geometry and blood viscosity, ... more Since resistance to flow is theoretically determined by arteriolar geometry and blood viscosity, we studied these two factors in 44 normal and 106 hypertensive subjects. Brachial bed vascular resistance was calculated as the ratio between mean pressure and brachial artery flow. Systemic blood viscosity in vitro was determined at 96 per s, while microvessel blood viscosity in vivo was estimated from the haematocrit-viscosity relationship at 240 per s. A resistive radius index was calculated which was only related to the microvessel viscosity: resistance ratio. Compared to normal subjects, hypertensive subjects had higher systemic in vitro blood viscosity (4.75 +/- 0.47 versus 4.50 +/- 0.43 mPa.s; P less than 0.005) and microvessel blood viscosity (2.60 +/- 0.21 versus 2.43 +/- 0.16 mPa.s; P less than 0.001). Hypertensive subjects also had a higher brachial vascular resistance (161 +/- 89 versus 124 +/- 58 mmHg/ml per s; P less than 0.01), but showed a similar resistive radius index (2.47 +/- 0.36 versus 2.57 +/- 0.35) compared to normal subjects. There was a positive correlation between systemic viscosity and brachial artery diameter and a negative correlation between microvessel viscosity and vascular resistance in the normotensive (P less than 0.05 and P less than 0.001, respectively) and hypertensive groups (P less than 0.001 and P less than 0.005, respectively). The resistive radius index was positively related to viscosity in normal and in hypertensive groups (P less than 0.001) but these relationships were significantly different (P less than 0.001), showing that, at the highest viscosities, arterial radius increased less in hypertensive than in normal subjects. Thus, the level of blood viscosity might influence arterial diameter.(ABSTRACT TRUNCATED AT 250 WORDS)
Radiology, 2002
To compare the effects on the myometrium of polyvinyl alcohol (PVA) particles and calibrated micr... more To compare the effects on the myometrium of polyvinyl alcohol (PVA) particles and calibrated microspheres (MS) in embolization of the uterine arteries in sheep. Superselective and bilateral embolization of the uterine arteries was performed with PVA particles and calibrated MS within 24 hours after artificial ovulation in 26 adult nonpregnant sheep. PVA particles of four diameters, 150-250, 250-400, 400-600, and 600-1,000 microm, were compared with calibrated MS of similar diameters, 100-300, 300-500, 500-700, and 700-900 microm, in eight groups of sheep. Evaluation was based on histopathologic study of uterus, ovaries, and vascular pedicles after sacrifice 5 days after embolization. The scores of necrosis, the diameter of occluded arteries, and the number of particles were determined. The scores of uterine necrosis were compared by using nonparametric tests (Mann-Whitney U and Kruskal-Wallis). Spearman rank test was used for correlations. PVA particles clumped more readily than did MS. Small particles had a higher score (P =.02) of uterine necrosis than did large particles. PVA particles produced more necrosis than did MS. Size of MS and diameter of occluded arteries showed significant correlation (rho = 0.762, P <.001). Size of PVA particles and diameter of occluded arteries showed no correlation. PVA particles occluded vessels of a wider range of size than did calibrated MS. PVA particles are associated with intense uterine necrosis and extensive arterial occlusion regardless of size. Calibrated MS, which are associated with less uterine necrosis, permit a segmental arterial occlusion correlated with size.
Medical Devices: Evidence and Research, 2014
Central venous device infections are associated with increased physical and psychological morbidi... more Central venous device infections are associated with increased physical and psychological morbidity, mortality, length of stay, and costs. The aim of this study was to prove the efficacy of pulsatile flushing to prevent the bacterial colonization of vascular access devices. One hundred and forty four tests using 576 polyurethane short venous access catheters were performed. Four catheters per test were polluted with a fibronectin-serum albumin solution. Three were filled with a Staphylococcus aureus broth; one served as negative control. One contaminated catheter was not flushed (positive control), and two were flushed (10 mL.sec(-1)) with normal saline solution, either by ten successive boluses of 1 mL each or by one bolus of 10 mL. Each catheter was cultivated. The S. aureus quantity observed after continuous flushing was significantly higher than that observed after pulsative flushing (P<0.001). Unflushed catheters were 20.71 and 6.42 times more polluted than catheters flushed with the pulsative method or the continuous method, respectively. Pulsative flushing was at least twice as effective as continuous flushing in reducing the S. aureus count. Pulsative flushing is more effective than continuous flushing in reducing the endoluminal contamination. Pulsative flushing is a simple, effective, and inexpensive technique to reduce catheter bacterial colonization.
Medical Devices: Evidence and Research, 2014
Now widely used, totally implantable venous access devices allow mid- and long-term, frequent, re... more Now widely used, totally implantable venous access devices allow mid- and long-term, frequent, repeated, or continuous injection of therapeutic products by vascular, cavitary, or perineural access. The effective flushing of these devices is a key factor that ensures their long-lasting use. We present experimental results and a numerical simulation to demonstrate that the implementation of rounded edge wall cavities improves flushing efficiency. We use the same approaches to suggest that the deposit amount may be reduced by the use of rounded edge wall cavities.
The Journal of Vascular Access, 2011
To compare, under controlled conditions similar to practical situations, the efficacy of pulsed a... more To compare, under controlled conditions similar to practical situations, the efficacy of pulsed and continuous infusion for flushing IVADs. For both of them different flow rates, flushing volumes, and times were tested. The PU catheter lumens were filled with a mixture of fibronectin and bovine albumin to simulate physiologic protein depot. Flushing was performed with normal saline. An adapted pump controlled the flow rates. Efficacy was measured by the amount of albumin recovered from the lumen of the tested devices. Flow rate, volumes, and times tested were based upon values reported and/or measured in nursing practices. We compared: (A) single 10 mL bolus and 6 flushing times, (B) continuous infusion of 500 mL in 24 hours, (C) 10 successive boluses 1 mL flushed in 0.5 s each and 6 different time intervals between each bolus. Statistics were performed using the Mann and Whitney U test. In group A, the maximum percentage of recovered protein (79.1% was achieved with the 10 mL bolus flushed in 2.5. In group B, 77% of protein was recovered at 24h. In group C: maximum efficacy (90 +/- 3%) was obtained when the time interval between 2 boluses was 0.4 s. We conclude that hydrodynamics has a determinant effect on the efficacy and that the adjunction of an intermittent component in the flow increases it. Flow type and the time interval between 2 boluses are the 2 critical variables.
Supersonic ShearWave Imaging (SSI) is based on two major concepts: ultrasound radiation force and... more Supersonic ShearWave Imaging (SSI) is based on two major concepts: ultrasound radiation force and ultrafast imaging. SSI provides a quantitative mapping of the stiffness of soft tissues in real-time. For cardiac applications, the complex structure of the myocardium (anisotropic and viscoelastic medium) induces the propagation of multiple shear waves mainly due to the fiber orientation. The aim of this study is to provide complete numerical tools to simulate a shear wave front in anisotropic media from the description of an ultrasonic transducer. Such numerical results provide a full description of shear wave propagation in anisotropic and viscoelastic biological soft tissues. The first step consists in a numerical design of the ultrasound probe in order to create a virtual but realistic source by means of ultrasound radiation force simulation. The second step uses this source in a Green's functions formalism [Vavryčuk 2007] to simulate shear wave propagation in a transverse isot...
Journal des Maladies Vasculaires
Clinical hemorheology and microcirculation
Although cardiac and vascular complications have been recognized among patients infected with the... more Although cardiac and vascular complications have been recognized among patients infected with the Human Immunodeficiency Virus-1 (HIV-1), their vascular biology and rheology have not been studied. Rheology of red blood cells (RBC) was assessed with an erythroaggregometer in 22 HIV-1 infected asymptomatic patients (pts) and 17 healthy HIV negative controls (C). All participants were normotensive, nondiabetics, had normal lipid levels and had an hematocrit ranging from 37 to 44% and hemoglobin levels > or = 12 g/100 ml. Patients had a shorter RBC aggregation characteristic time than controls (1.49 +/- 0.17 vs. 2.04 +/- 0.41 s, p = 0.001) and an increased disaggregation shear rate (166 +/- 34.9 vs. 122 +/- 25.4 s(-1), p = 0.001). This hyperaggregation tendancy was associated with increased gamma-globulin (18.3 +/- 3.3 vs. 13.7 +/- 1.9 g/l, p = 0.01) and fibrinogen (3.52 +/- 0.57 vs 3.03 +/- 0.48 g/l, p = 0.003) levels and with an increased erythrocyte sedimentation rate (ESR) (25 +/...
Applied Rheology
The grouts are suspensions containing cement used in the technique of prestressing by post-tensio... more The grouts are suspensions containing cement used in the technique of prestressing by post-tension. Cement, from its chemical nature, protects the wire ropes (strands) from corrosion. To be able to play correctly this protective role, the grout must remain homogeneous and must entirely cover the strands. The lack of stability of the grouts, which results in packing or sedimentation, is a major problem. In this article, we try to correlate the rheological properties of the grout with its capacity to remain homogeneous. We show that an increase in the concentration of superplasticizer, a polymer solution, decreases the thixotropic behavior of the grout, but on the other hand, increases the effects of sedimentation. We explain this phenomenon by the modification of the structure of a three-dimensional network in relation to the interparticle interactions.
Comptes Rendus Mecanique
We present an experimental setup representing muscular draining in the lower leg. A collapsible t... more We present an experimental setup representing muscular draining in the lower leg. A collapsible tube is placed vertically in a hermetic chamber connected to a variable pressure tank. With the help of electrovalves we study a draining corresponding to walking. When the external pressure is raised a phenomenon of flow limitation appears and the draining time is very long. We also present numerical simulations showing that a critical passage subcritical supercritical originates the flow limitation.
2013 IEEE International Ultrasonics Symposium (IUS), 2013
ABSTRACT Deep venous thrombosis (DVT) affects millions of people worldwide. Its diagnosis and tre... more ABSTRACT Deep venous thrombosis (DVT) affects millions of people worldwide. Its diagnosis and treatment depends on clot's age which is closely related to its viscoelastic properties. In this study we use Supersonic Shear Wave Imaging (SSI) and classical rheometry to measure the evolution of the viscoelastic properties of blood clots. Using SSI and shear wave spectroscopy (SWS), dispersion curves were obtained between 50 and 300 Hz every minute for 2 hours during coagulation. Using the values for G' and G" from the rheological studies, the theoretical shear wave speeds were calculated for frequencies between 0.25 and 30 Hz at the same time points. Maxwell, Voigt and Zener models were fitted to the dispersion data obtained by combining both techniques. Shear wave speed showed a marked increase with time of coagulation for all the frequencies, from around 0.5 m/s at the beginning of coagulation to 0.9 after 2 hours. The Zener model (μ1, μ2, η) showed the best fit on the data out of the 3 models. Even though the Maxwell (μM, μη) and Voigt (μV, ηV) models did a good job at higher frequencies (70 Hz and up), both models failed to characterize the lower frequencies. Combination of SSI and classical rheometry allowed the characterization of the viscoelastic properties of blood clots in a very large frequency range between 0.25 Hz and 300 Hz. The two techniques showed very good agreement suggesting that SSI could be used to study the rheological properties of soft solids.
Ultrasound in Medicine & Biology, 2012
Deep venous thrombosis (DVT) affects millions of people worldwide. A fatal complication occurs wh... more Deep venous thrombosis (DVT) affects millions of people worldwide. A fatal complication occurs when the thrombi detach and create a pulmonary embolism. The diagnosis and treatment of DVT depends on clot's age. The elasticity of thrombi is closely related to its age. Blood was collected from pigs and anticoagulated using ethylenediaminetetraacetic acid (EDTA). Coagulation was initiated using calcium ions. Supersonic shear wave imaging was used to generate shear waves using 100 ms tone bursts of 8 MHz. Tracking of the shear waves was done by ultrafast imaging. Postprocessing of the data was done using Matlab Ò . Two-dimensional (2-D) maps of elasticity were obtained by calculating the speed of shear wave propagation. Elasticity varied with time from around 50 Pa at coagulation to 1600 Pa at 120 min after which the elasticity showed a natural decreased (17%) because of thrombolytic action of plasmin. Ejection of the serum from the clot showed a significant decrease in the elasticity of the clot next to the liquid pool (65% decrease), corresponding to the detachment of the clot from the beaker wall. The use of a thrombolytic agent (Urokinase) on the coagulated blood decreased the shear elasticity close to the point of injection, which varied with time and distance. Supersonic imaging proved to be useful mapping the 2-D clot's elasticity. It allowed the visualization of the heterogeneity of mechanical properties of thrombi and has potential use in predicting thrombi breakage as well as in monitoring thrombolytic therapy.
Ultrasound in Medicine & Biology, 2013
The assessment of coagulating blood elasticity has gained importance as a result of several studi... more The assessment of coagulating blood elasticity has gained importance as a result of several studies that have correlated it to cardiovascular pathologic conditions. In this study we use supersonic shear wave imaging (SSI) to measure viscoelastic properties of blood clots. At the same time, classical rheometry experiments were carried out on the same blood samples taken within the first few seconds of coagulation. Using SSI, phase velocities of the shear wave indicated increasing dispersion with time. In all cases, the frequency bandwidth of propagating shear waves changed from 20-50 Hz at the first few min of coagulation to around 300 Hz toward the end of experiments. Using the values of G' and G″ from the rheometry studies, the theoretical shear wave velocities were calculated and correlated with SSI measurements. Results of the two techniques were in very good agreement, confirming that SSI provides accurate measurements of viscoelastic properties as corroborated by conventional rheometric measurements.
Respiratory Physiology & Neurobiology, 2014
Our objective was to evaluate whether a decrease in the homothety ratio (h: diameter of child/par... more Our objective was to evaluate whether a decrease in the homothety ratio (h: diameter of child/parent bronchus, constant over generations) explains the shift in airway resistance toward periphery in chronic obstructive pulmonary disease (COPD). Using a validated computational model of fluid motion, we determined that reduced values of h (<0.76) were associated with a shift in resistance toward periphery. The calculated luminal diameters of terminal bronchioles using normal h (0.80-0.85) or reduced h (0.70-0.75) fitted well with measured micro-CT values obtained by McDonough et al. (N. Engl. J. Med., 2011; 365:1567-75) in control and COPD patients, respectively. A semi-analytic formula of resistance using tracheal dimensions and h was developed, and using experimental data (tracheal area and h from patients [Bokov et al., Respir. Physiol. Neurobiol., 2010; 173:1-10]), we verified the agreement between measured and calculated resistance (r = 0.42). In conclusion, the remodeling process of COPD may reduce h and explain the shift in resistance toward lung periphery.
Radiology, 2002
To compare the effects on the myometrium of polyvinyl alcohol (PVA) particles and calibrated micr... more To compare the effects on the myometrium of polyvinyl alcohol (PVA) particles and calibrated microspheres (MS) in embolization of the uterine arteries in sheep. Superselective and bilateral embolization of the uterine arteries was performed with PVA particles and calibrated MS within 24 hours after artificial ovulation in 26 adult nonpregnant sheep. PVA particles of four diameters, 150-250, 250-400, 400-600, and 600-1,000 microm, were compared with calibrated MS of similar diameters, 100-300, 300-500, 500-700, and 700-900 microm, in eight groups of sheep. Evaluation was based on histopathologic study of uterus, ovaries, and vascular pedicles after sacrifice 5 days after embolization. The scores of necrosis, the diameter of occluded arteries, and the number of particles were determined. The scores of uterine necrosis were compared by using nonparametric tests (Mann-Whitney U and Kruskal-Wallis). Spearman rank test was used for correlations. PVA particles clumped more readily than did MS. Small particles had a higher score (P =.02) of uterine necrosis than did large particles. PVA particles produced more necrosis than did MS. Size of MS and diameter of occluded arteries showed significant correlation (rho = 0.762, P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;.001). Size of PVA particles and diameter of occluded arteries showed no correlation. PVA particles occluded vessels of a wider range of size than did calibrated MS. PVA particles are associated with intense uterine necrosis and extensive arterial occlusion regardless of size. Calibrated MS, which are associated with less uterine necrosis, permit a segmental arterial occlusion correlated with size.
ISRN Vascular Medicine, 2012
One particular characteristic of peripherally central catheter (PCC), peripherally inserted centr... more One particular characteristic of peripherally central catheter (PCC), peripherally inserted central catheter (PICC) or totally implantable venous access device (TIVAD), is to be submitted to a rotational movement around the shoulder in the daily routine. The aim of this paper is to show that these movements induce a variation of the inner volume of the catheter which may be responsible for an internal distal pollution of the lumen. The results are presented in the framework of an open discussion on the catheter protocols of use as well as a possible improvement of the materials.
La Houille Blanche, 2005
ABSTRACT Venous flow generates a large pressure gradient between lower limbs and the heart. In or... more ABSTRACT Venous flow generates a large pressure gradient between lower limbs and the heart. In order to correctly ensure blood circulation, several mechanisms coexist such as the plantar arch pump, the calf pump, breathing, walk accelerations and naturally, the heart action. These added mechanisms provide rapid variations of the wall vessels position and the fluctuations on the venous flow that have global effects on the circulatory flow. We developed a research program including an experimental set-up that could be numerically validated. Nevertheless, mechanical tube laws evaluation are image reconstruction dependent when tube collapses and it is thus necessary to compute areas precisely for a right validation of the tube dynamics. This communication introduces a new experimental set-up allowing strong vertical accelerations and also presents a new image reconstruction method to compute cross-section areas in collapsible tubes. Le débit veineux engendre un fort gradient de pression entre les membres inférieurs et le cœur. Afin d’assurer convenablement la circulation sanguine, différents mécanismes coexistent tels l’appui plantaire, la pompe du mollet, la respiration, les accélérations dues à la marche ainsi que l’action du cœur. Ces phénomènes conjoints induisent un déplacement rapide de la paroi des vaisseaux ainsi que des fluctuations de l’écoulement veineux ayant des effets globaux sur la circulation. Nous avons développé un programme de recherche incluant une partie expérimentale pouvant être validée numériquement. Les lois qui décrivent le comportement mécanique des tuyaux sont obtenues à l’aide de la reconstruction d’images lors du collabage du tube et impliquent un calcul précis sur les sections droites. Cette communication présente un nouveau dispositif expérimental acceptant de fortes accélérations verticales ainsi qu’une nouvelle méthode de reconstruction d’images permettant une mesure précise de l’aire de la section droite de tubes collabables.
La Houille Blanche, 2005
ABSTRACT During the pregnancy, the development and the fœtal growth depend on the placental vascu... more ABSTRACT During the pregnancy, the development and the fœtal growth depend on the placental vascularization by the maternal blood. The aim of this study is to achieve a better understanding of uteroplacental circulation physiopathology, the CFD enables us to reach information, usually inaccessible for ethical reasons or species specificity. We show a first simplified approach which proves the necessity of taking into consideration the blood rheological properties for the study of blood flows in the intervillous chamber. Tout au long de la grossesse, le développement et la croissance du fœtus dépendent de la vascularisation du placenta par le sang de la mère. L’objectif de ce travail est de permettre une meilleure compréhension de la physiopathologie de la circulation utéroplacentaire, l’outil numérique permettant d’atteindre des grandeurs habituellement non accessibles pour des raisons éthiques ou de spécificité d’espèce. On présente une première approche simplifiée qui démontre la nécessité de prendre en compte les propriétés rhéologiques du sang pour l'étude des écoulements sanguins dans la chambre intervilleuse.
AJR. American journal of roentgenology, 2014
Journal des maladies vasculaires, 2011
Compression therapy for venous and lymphatic edema of the lower limbs raises a major challenge co... more Compression therapy for venous and lymphatic edema of the lower limbs raises a major challenge concerning the optimal pressure ensuring both efficacy and patient compliance. We present a mathematical model of tissue fluid transfers which is aimed at determining the lowest pressure required to prevent edema. The model is based on a set of equations, derived from published experimental data, which describe the fluid and solute transfers between blood, interstitium and lymphatics, and the mechanical properties of interstitial compartment. It enables us to compute the changes in tissue volume, at the ankle level, resulting from increases of capillary pressure in case of venous insufficiency, and from an impairment of lymph drainage; as well as the effect of various external pressures upon this volume. An increase of capillary pressure to 40 and 50 mmHg results in an ankle edema which is completely prevented by an external pressure of 10 mmHg. This result is in keeping with the observati...
Journal of Hypertension, 1990
Since resistance to flow is theoretically determined by arteriolar geometry and blood viscosity, ... more Since resistance to flow is theoretically determined by arteriolar geometry and blood viscosity, we studied these two factors in 44 normal and 106 hypertensive subjects. Brachial bed vascular resistance was calculated as the ratio between mean pressure and brachial artery flow. Systemic blood viscosity in vitro was determined at 96 per s, while microvessel blood viscosity in vivo was estimated from the haematocrit-viscosity relationship at 240 per s. A resistive radius index was calculated which was only related to the microvessel viscosity: resistance ratio. Compared to normal subjects, hypertensive subjects had higher systemic in vitro blood viscosity (4.75 +/- 0.47 versus 4.50 +/- 0.43 mPa.s; P less than 0.005) and microvessel blood viscosity (2.60 +/- 0.21 versus 2.43 +/- 0.16 mPa.s; P less than 0.001). Hypertensive subjects also had a higher brachial vascular resistance (161 +/- 89 versus 124 +/- 58 mmHg/ml per s; P less than 0.01), but showed a similar resistive radius index (2.47 +/- 0.36 versus 2.57 +/- 0.35) compared to normal subjects. There was a positive correlation between systemic viscosity and brachial artery diameter and a negative correlation between microvessel viscosity and vascular resistance in the normotensive (P less than 0.05 and P less than 0.001, respectively) and hypertensive groups (P less than 0.001 and P less than 0.005, respectively). The resistive radius index was positively related to viscosity in normal and in hypertensive groups (P less than 0.001) but these relationships were significantly different (P less than 0.001), showing that, at the highest viscosities, arterial radius increased less in hypertensive than in normal subjects. Thus, the level of blood viscosity might influence arterial diameter.(ABSTRACT TRUNCATED AT 250 WORDS)
Radiology, 2002
To compare the effects on the myometrium of polyvinyl alcohol (PVA) particles and calibrated micr... more To compare the effects on the myometrium of polyvinyl alcohol (PVA) particles and calibrated microspheres (MS) in embolization of the uterine arteries in sheep. Superselective and bilateral embolization of the uterine arteries was performed with PVA particles and calibrated MS within 24 hours after artificial ovulation in 26 adult nonpregnant sheep. PVA particles of four diameters, 150-250, 250-400, 400-600, and 600-1,000 microm, were compared with calibrated MS of similar diameters, 100-300, 300-500, 500-700, and 700-900 microm, in eight groups of sheep. Evaluation was based on histopathologic study of uterus, ovaries, and vascular pedicles after sacrifice 5 days after embolization. The scores of necrosis, the diameter of occluded arteries, and the number of particles were determined. The scores of uterine necrosis were compared by using nonparametric tests (Mann-Whitney U and Kruskal-Wallis). Spearman rank test was used for correlations. PVA particles clumped more readily than did MS. Small particles had a higher score (P =.02) of uterine necrosis than did large particles. PVA particles produced more necrosis than did MS. Size of MS and diameter of occluded arteries showed significant correlation (rho = 0.762, P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;.001). Size of PVA particles and diameter of occluded arteries showed no correlation. PVA particles occluded vessels of a wider range of size than did calibrated MS. PVA particles are associated with intense uterine necrosis and extensive arterial occlusion regardless of size. Calibrated MS, which are associated with less uterine necrosis, permit a segmental arterial occlusion correlated with size.
Medical Devices: Evidence and Research, 2014
Central venous device infections are associated with increased physical and psychological morbidi... more Central venous device infections are associated with increased physical and psychological morbidity, mortality, length of stay, and costs. The aim of this study was to prove the efficacy of pulsatile flushing to prevent the bacterial colonization of vascular access devices. One hundred and forty four tests using 576 polyurethane short venous access catheters were performed. Four catheters per test were polluted with a fibronectin-serum albumin solution. Three were filled with a Staphylococcus aureus broth; one served as negative control. One contaminated catheter was not flushed (positive control), and two were flushed (10 mL.sec(-1)) with normal saline solution, either by ten successive boluses of 1 mL each or by one bolus of 10 mL. Each catheter was cultivated. The S. aureus quantity observed after continuous flushing was significantly higher than that observed after pulsative flushing (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.001). Unflushed catheters were 20.71 and 6.42 times more polluted than catheters flushed with the pulsative method or the continuous method, respectively. Pulsative flushing was at least twice as effective as continuous flushing in reducing the S. aureus count. Pulsative flushing is more effective than continuous flushing in reducing the endoluminal contamination. Pulsative flushing is a simple, effective, and inexpensive technique to reduce catheter bacterial colonization.
Medical Devices: Evidence and Research, 2014
Now widely used, totally implantable venous access devices allow mid- and long-term, frequent, re... more Now widely used, totally implantable venous access devices allow mid- and long-term, frequent, repeated, or continuous injection of therapeutic products by vascular, cavitary, or perineural access. The effective flushing of these devices is a key factor that ensures their long-lasting use. We present experimental results and a numerical simulation to demonstrate that the implementation of rounded edge wall cavities improves flushing efficiency. We use the same approaches to suggest that the deposit amount may be reduced by the use of rounded edge wall cavities.
The Journal of Vascular Access, 2011
To compare, under controlled conditions similar to practical situations, the efficacy of pulsed a... more To compare, under controlled conditions similar to practical situations, the efficacy of pulsed and continuous infusion for flushing IVADs. For both of them different flow rates, flushing volumes, and times were tested. The PU catheter lumens were filled with a mixture of fibronectin and bovine albumin to simulate physiologic protein depot. Flushing was performed with normal saline. An adapted pump controlled the flow rates. Efficacy was measured by the amount of albumin recovered from the lumen of the tested devices. Flow rate, volumes, and times tested were based upon values reported and/or measured in nursing practices. We compared: (A) single 10 mL bolus and 6 flushing times, (B) continuous infusion of 500 mL in 24 hours, (C) 10 successive boluses 1 mL flushed in 0.5 s each and 6 different time intervals between each bolus. Statistics were performed using the Mann and Whitney U test. In group A, the maximum percentage of recovered protein (79.1% was achieved with the 10 mL bolus flushed in 2.5. In group B, 77% of protein was recovered at 24h. In group C: maximum efficacy (90 +/- 3%) was obtained when the time interval between 2 boluses was 0.4 s. We conclude that hydrodynamics has a determinant effect on the efficacy and that the adjunction of an intermittent component in the flow increases it. Flow type and the time interval between 2 boluses are the 2 critical variables.
Supersonic ShearWave Imaging (SSI) is based on two major concepts: ultrasound radiation force and... more Supersonic ShearWave Imaging (SSI) is based on two major concepts: ultrasound radiation force and ultrafast imaging. SSI provides a quantitative mapping of the stiffness of soft tissues in real-time. For cardiac applications, the complex structure of the myocardium (anisotropic and viscoelastic medium) induces the propagation of multiple shear waves mainly due to the fiber orientation. The aim of this study is to provide complete numerical tools to simulate a shear wave front in anisotropic media from the description of an ultrasonic transducer. Such numerical results provide a full description of shear wave propagation in anisotropic and viscoelastic biological soft tissues. The first step consists in a numerical design of the ultrasound probe in order to create a virtual but realistic source by means of ultrasound radiation force simulation. The second step uses this source in a Green's functions formalism [Vavryčuk 2007] to simulate shear wave propagation in a transverse isot...
Journal des Maladies Vasculaires
Clinical hemorheology and microcirculation
Although cardiac and vascular complications have been recognized among patients infected with the... more Although cardiac and vascular complications have been recognized among patients infected with the Human Immunodeficiency Virus-1 (HIV-1), their vascular biology and rheology have not been studied. Rheology of red blood cells (RBC) was assessed with an erythroaggregometer in 22 HIV-1 infected asymptomatic patients (pts) and 17 healthy HIV negative controls (C). All participants were normotensive, nondiabetics, had normal lipid levels and had an hematocrit ranging from 37 to 44% and hemoglobin levels > or = 12 g/100 ml. Patients had a shorter RBC aggregation characteristic time than controls (1.49 +/- 0.17 vs. 2.04 +/- 0.41 s, p = 0.001) and an increased disaggregation shear rate (166 +/- 34.9 vs. 122 +/- 25.4 s(-1), p = 0.001). This hyperaggregation tendancy was associated with increased gamma-globulin (18.3 +/- 3.3 vs. 13.7 +/- 1.9 g/l, p = 0.01) and fibrinogen (3.52 +/- 0.57 vs 3.03 +/- 0.48 g/l, p = 0.003) levels and with an increased erythrocyte sedimentation rate (ESR) (25 +/...
Applied Rheology
The grouts are suspensions containing cement used in the technique of prestressing by post-tensio... more The grouts are suspensions containing cement used in the technique of prestressing by post-tension. Cement, from its chemical nature, protects the wire ropes (strands) from corrosion. To be able to play correctly this protective role, the grout must remain homogeneous and must entirely cover the strands. The lack of stability of the grouts, which results in packing or sedimentation, is a major problem. In this article, we try to correlate the rheological properties of the grout with its capacity to remain homogeneous. We show that an increase in the concentration of superplasticizer, a polymer solution, decreases the thixotropic behavior of the grout, but on the other hand, increases the effects of sedimentation. We explain this phenomenon by the modification of the structure of a three-dimensional network in relation to the interparticle interactions.
Comptes Rendus Mecanique
We present an experimental setup representing muscular draining in the lower leg. A collapsible t... more We present an experimental setup representing muscular draining in the lower leg. A collapsible tube is placed vertically in a hermetic chamber connected to a variable pressure tank. With the help of electrovalves we study a draining corresponding to walking. When the external pressure is raised a phenomenon of flow limitation appears and the draining time is very long. We also present numerical simulations showing that a critical passage subcritical supercritical originates the flow limitation.
2013 IEEE International Ultrasonics Symposium (IUS), 2013
ABSTRACT Deep venous thrombosis (DVT) affects millions of people worldwide. Its diagnosis and tre... more ABSTRACT Deep venous thrombosis (DVT) affects millions of people worldwide. Its diagnosis and treatment depends on clot's age which is closely related to its viscoelastic properties. In this study we use Supersonic Shear Wave Imaging (SSI) and classical rheometry to measure the evolution of the viscoelastic properties of blood clots. Using SSI and shear wave spectroscopy (SWS), dispersion curves were obtained between 50 and 300 Hz every minute for 2 hours during coagulation. Using the values for G' and G" from the rheological studies, the theoretical shear wave speeds were calculated for frequencies between 0.25 and 30 Hz at the same time points. Maxwell, Voigt and Zener models were fitted to the dispersion data obtained by combining both techniques. Shear wave speed showed a marked increase with time of coagulation for all the frequencies, from around 0.5 m/s at the beginning of coagulation to 0.9 after 2 hours. The Zener model (μ1, μ2, η) showed the best fit on the data out of the 3 models. Even though the Maxwell (μM, μη) and Voigt (μV, ηV) models did a good job at higher frequencies (70 Hz and up), both models failed to characterize the lower frequencies. Combination of SSI and classical rheometry allowed the characterization of the viscoelastic properties of blood clots in a very large frequency range between 0.25 Hz and 300 Hz. The two techniques showed very good agreement suggesting that SSI could be used to study the rheological properties of soft solids.
Ultrasound in Medicine & Biology, 2012
Deep venous thrombosis (DVT) affects millions of people worldwide. A fatal complication occurs wh... more Deep venous thrombosis (DVT) affects millions of people worldwide. A fatal complication occurs when the thrombi detach and create a pulmonary embolism. The diagnosis and treatment of DVT depends on clot's age. The elasticity of thrombi is closely related to its age. Blood was collected from pigs and anticoagulated using ethylenediaminetetraacetic acid (EDTA). Coagulation was initiated using calcium ions. Supersonic shear wave imaging was used to generate shear waves using 100 ms tone bursts of 8 MHz. Tracking of the shear waves was done by ultrafast imaging. Postprocessing of the data was done using Matlab Ò . Two-dimensional (2-D) maps of elasticity were obtained by calculating the speed of shear wave propagation. Elasticity varied with time from around 50 Pa at coagulation to 1600 Pa at 120 min after which the elasticity showed a natural decreased (17%) because of thrombolytic action of plasmin. Ejection of the serum from the clot showed a significant decrease in the elasticity of the clot next to the liquid pool (65% decrease), corresponding to the detachment of the clot from the beaker wall. The use of a thrombolytic agent (Urokinase) on the coagulated blood decreased the shear elasticity close to the point of injection, which varied with time and distance. Supersonic imaging proved to be useful mapping the 2-D clot's elasticity. It allowed the visualization of the heterogeneity of mechanical properties of thrombi and has potential use in predicting thrombi breakage as well as in monitoring thrombolytic therapy.
Ultrasound in Medicine & Biology, 2013
The assessment of coagulating blood elasticity has gained importance as a result of several studi... more The assessment of coagulating blood elasticity has gained importance as a result of several studies that have correlated it to cardiovascular pathologic conditions. In this study we use supersonic shear wave imaging (SSI) to measure viscoelastic properties of blood clots. At the same time, classical rheometry experiments were carried out on the same blood samples taken within the first few seconds of coagulation. Using SSI, phase velocities of the shear wave indicated increasing dispersion with time. In all cases, the frequency bandwidth of propagating shear waves changed from 20-50 Hz at the first few min of coagulation to around 300 Hz toward the end of experiments. Using the values of G&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; and G″ from the rheometry studies, the theoretical shear wave velocities were calculated and correlated with SSI measurements. Results of the two techniques were in very good agreement, confirming that SSI provides accurate measurements of viscoelastic properties as corroborated by conventional rheometric measurements.
Respiratory Physiology & Neurobiology, 2014
Our objective was to evaluate whether a decrease in the homothety ratio (h: diameter of child/par... more Our objective was to evaluate whether a decrease in the homothety ratio (h: diameter of child/parent bronchus, constant over generations) explains the shift in airway resistance toward periphery in chronic obstructive pulmonary disease (COPD). Using a validated computational model of fluid motion, we determined that reduced values of h (<0.76) were associated with a shift in resistance toward periphery. The calculated luminal diameters of terminal bronchioles using normal h (0.80-0.85) or reduced h (0.70-0.75) fitted well with measured micro-CT values obtained by McDonough et al. (N. Engl. J. Med., 2011; 365:1567-75) in control and COPD patients, respectively. A semi-analytic formula of resistance using tracheal dimensions and h was developed, and using experimental data (tracheal area and h from patients [Bokov et al., Respir. Physiol. Neurobiol., 2010; 173:1-10]), we verified the agreement between measured and calculated resistance (r = 0.42). In conclusion, the remodeling process of COPD may reduce h and explain the shift in resistance toward lung periphery.
Radiology, 2002
To compare the effects on the myometrium of polyvinyl alcohol (PVA) particles and calibrated micr... more To compare the effects on the myometrium of polyvinyl alcohol (PVA) particles and calibrated microspheres (MS) in embolization of the uterine arteries in sheep. Superselective and bilateral embolization of the uterine arteries was performed with PVA particles and calibrated MS within 24 hours after artificial ovulation in 26 adult nonpregnant sheep. PVA particles of four diameters, 150-250, 250-400, 400-600, and 600-1,000 microm, were compared with calibrated MS of similar diameters, 100-300, 300-500, 500-700, and 700-900 microm, in eight groups of sheep. Evaluation was based on histopathologic study of uterus, ovaries, and vascular pedicles after sacrifice 5 days after embolization. The scores of necrosis, the diameter of occluded arteries, and the number of particles were determined. The scores of uterine necrosis were compared by using nonparametric tests (Mann-Whitney U and Kruskal-Wallis). Spearman rank test was used for correlations. PVA particles clumped more readily than did MS. Small particles had a higher score (P =.02) of uterine necrosis than did large particles. PVA particles produced more necrosis than did MS. Size of MS and diameter of occluded arteries showed significant correlation (rho = 0.762, P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;.001). Size of PVA particles and diameter of occluded arteries showed no correlation. PVA particles occluded vessels of a wider range of size than did calibrated MS. PVA particles are associated with intense uterine necrosis and extensive arterial occlusion regardless of size. Calibrated MS, which are associated with less uterine necrosis, permit a segmental arterial occlusion correlated with size.