marianne fenech | University of Ottawa | Université d'Ottawa (original) (raw)
Papers by marianne fenech
Frontiers in Physiology
Predicting blood microflow in both simple and complex geometries is challenging because of the co... more Predicting blood microflow in both simple and complex geometries is challenging because of the composition and behavior of the blood at microscale. However, characterization of the velocity in microchannels is the key for gaining insights into cellular interactions at the microscale, mechanisms of diseases, and efficacy of therapeutic solutions. Image-based measurement techniques are a subset of methods for measuring the local flow velocity that typically utilize tracer particles for flow visualization. In the most basic form, a high-speed camera and microscope setup are the only requirements for data acquisition; however, the development of image processing algorithms and equipment has made current image-based techniques more sophisticated. This mini review aims to provide a succinct and accessible overview of image-based experimental measurement techniques to characterize the velocity field of blood microflow. The following techniques are introduced: cell tracking velocimetry, kym...
Lab on a Chip, 2019
A one-mask microfabrication process to build artificial vascular networks for the analysis of blo... more A one-mask microfabrication process to build artificial vascular networks for the analysis of blood flows and hemophysics.
The Journal of the Acoustical Society of America, 2021
Chinchilla et al. Although quantitative ultrasound techniques based on the parameterization of th... more Chinchilla et al. Although quantitative ultrasound techniques based on the parameterization of the backscatter coefficient (BSC) have been successfully applied to blood characterization, theoretical scattering models assume blood as an isotropic scattering medium. However, the red blood cell (RBC) aggregates form anisotropic structures such as rouleaux. The present study proposes an anisotropic formulation of the Effective Medium Theory combined with the Local Monodisperse Approximation (EMTLMA) that considers perfectly aligned prolate-shaped aggregates. Theoretical BSC predictions were first compared with computer simulations of BSCs in a forward problem framework. Computer simulations were conducted for perfectly aligned prolate-shaped aggregates and more complex configurations with partially aligned prolate-shaped aggregates for which the size and orientation of RBC aggregates were obtained from blood optical observations. The isotropic and anisotropic EMTLMA models were then compared in an inverse problem framework to estimate blindly the structural parameters of RBC aggregates from the simulated BSCs. When considering the isotropic EMTLMA, the use of averaged BSCs over different insonification directions significantly improves the estimation of aggregate structural parameters. Overall, the anisotropic EMTLMA was found to be superior to the isotropic EMTLMA in estimating the scatterer volume distribution. These results contribute to a better interpretation of scatterer size estimates for blood characterization.
2017 IEEE International Symposium on Medical Measurements and Applications (MeMeA), 2017
We have designed and fabricated a biomicroviscometer platform for measurement of microflows of bi... more We have designed and fabricated a biomicroviscometer platform for measurement of microflows of biological fluids. The biomicroviscometer combines an optically clear biocompatible polydimethylsiloxane (PDMS) channel with on-chip integrated microfluidic differential pressure sensors and capabilities of modular channel geometries. This setup allows for a direct measurement of the change in pressure and flow rate, increasing the overall accuracy of the measurement of viscosity and optical observation. We present an introduction of this combined method of measurement with different channel dimensions, using Newtonian and non-Newtonian fluids, and the corresponding calculations. This measurement technique has potential applications in measuring rheological properties at the micro level to further blood disease analysis, and lab-on-a-chip fabrication and analysis.
Stenosis or incompetence at severe levels reduce the performance of the heart and place additiona... more Stenosis or incompetence at severe levels reduce the performance of the heart and place additional stress and strain upon it. Therefore, in many cases, surgical replacement of the diseased valve with a Bioprosthetic or Mechanical Heart Valves (MHV) is necessary to restore valve function. Although the lifelong anticoagulant medication and the possible clinical complications (e.g. blood elements damage and/or thrombus formation), Bileaflet MHV are the most implanted valves with over 170,000 implants worldwide each year as a result of high durability and appropriate characteristics for blood hemodynamics (in terms of low pressure gradient and low shear stress level)[1]. Unfortunately, in some cases, Thromboembolic complications and/or pannus formation are possible after Bileaflet valve implantation. The mortality percentage for the reoperation might be as high as 69%. By the way, even though the low percentage of the deficiency in one or both leaflets(0.2%-6% per patient-year), the dan...
This work aims to develop a method to quantitatively analyze red blood cell (RBC) aggregates unde... more This work aims to develop a method to quantitatively analyze red blood cell (RBC) aggregates under controlled flow conditions, based on image processing. The set up consists of RBC suspensions entrained by a second fluid in a 150x33 μm microchannel. The experiments are performed by varying the hematocrit (10, 15 & 20%) and the flow rate (Q=5 & 10 μl/hr). The flow is visualized using a high speed camera coupled to a micro Particle Image Velocimetry (μPIV) system. Videos obtained with the high speed camera are processed using a MATLAB program to detect RBC aggregates based on the images intensities. An average aggregate size has been determined for each of the shear rates and hematocrits. The aggregates are shown to be larger at low flow rates and high hematocrits.
Medical Engineering & Physics, 2019
The wall adhesion of 1 µm microparticles in human blood was studied in circular microchannels. Th... more The wall adhesion of 1 µm microparticles in human blood was studied in circular microchannels. The level of particle wall adhesion was measured for varying levels of shear rate and varying degrees of red blood cell aggregation, which was modulated by the addition of macromolecule dextran 500. The blood preparations were injected into PDMS microfluidic devices that were modified to have circular channels, better matching the geometry of physiological microcirculation compared to square channels or Couette flow systems. The circular walls of the microchannels were embedded with biotinylated phospholipids to which marginating microspheres coated with streptavidin bound. The particle wall adhesion was evaluated by counting the particles that adhered to the channel's wall after flushing the channel. Blood preparations of five dextran concentrations (including baseline case of 0%) were tested for four flow velocities, to quantify the effects of aggregation for varying shear rate. It was found that the level of particle wall adhesion was positively correlated with the level of RBC aggregation, particularly at low shear rates, when aggregation was enhanced. The particle adhesion was especially enhanced at aggregation levels in the range of physiological aggregation levels of whole blood, suggesting that RBC aggregation plays an important role in the dynamics of platelets and leukocytes in vivo.
International Journal of Molecular Sciences
Patients with sickle cell disease (SCD) have poorly deformable red blood cells (RBC) that may imp... more Patients with sickle cell disease (SCD) have poorly deformable red blood cells (RBC) that may impede blood flow into microcirculation. Very few studies have been able to directly visualize microcirculation in humans with SCD. Sublingual video microscopy was performed in eight healthy (HbAA genotype) and four sickle cell individuals (HbSS genotype). Their hematocrit, blood viscosity, red blood cell deformability, and aggregation were individually determined through blood sample collections. Their microcirculation morphology (vessel density and diameter) and microcirculation hemodynamics (local velocity, local viscosity, and local red blood cell deformability) were investigated. The De Backer score was higher (15.9 mm−1) in HbSS individuals compared to HbAA individuals (11.1 mm−1). RBC deformability, derived from their local hemodynamic condition, was lower in HbSS individuals compared to HbAA individuals for vessels < 20 μm. Despite the presence of more rigid RBCs in HbSS individu...
PLOS ONE
Red blood cells (RBCs) are the most abundant cells in human blood. Remarkably RBCs deform and bri... more Red blood cells (RBCs) are the most abundant cells in human blood. Remarkably RBCs deform and bridge together to form aggregates under very low shear rates. The theory and mechanics behind aggregation are, however, not yet completely understood. The main objective of this work is to quantify and characterize RBC aggregates in order to enhance the current understanding of the non-Newtonian behaviour of blood in microcirculation. Suspensions of human blood were flowed and observed in vitro in poly-di-methyl-siloxane (PDMS) microchannels to characterize RBC aggregates. These microchannels were fabricated using standard photolithography methods. Experiments were performed using a micro particle image velocimetry (μPIV) system for shear rate measurements, coupled with a high-speed camera for flow visualization. RBC aggregate sizes were quantified in controlled and measurable shear rate environments for 5, 10 and 15% hematocrit. Aggregate sizes were determined using image processing techniques, while apparent viscosity was measured using optical viscometry. For the samples suspended at 5% H, aggregate size was not strongly correlated with shear rate. For the 10% H suspensions, in contrast, lowering the shear rate below 10 s-1 resulted in a significant increase of RBC aggregate sizes. The viscosity was found to increase with decreasing shear rate and increasing hematocrit, exemplifying the established non-Newtonian shear-thinning behaviour of blood. Increase in aggregation size did not translate into a linear increase of the blood viscosity. Temperature was shown to affect blood viscosity as expected, however, no correlation for aggregate size with temperature was observed. Non-Newtonian parameters associated with power law and Carreau models were determined by fitting the experimental data and can be used towards the simple modeling of blood's non-Newtonian behaviour in microcirculation. This work establishes a relationship between RBC aggregate sizes and corresponding shear rates and one between RBC aggregate sizes and apparent blood viscosity at body and room temperatures, in a microfluidic environment for low hematocrit. Effects of hematocrit, shear rate, viscosity and temperature on RBC aggregate sizes have been quantified.
International Journal of Heat and Mass Transfer, 2016
Itbm Rbm, Oct 1, 2004
We have measured extracellular (VE) and total water (VT) volumes in 17 dialysed patients for a to... more We have measured extracellular (VE) and total water (VT) volumes in 17 dialysed patients for a total of 46 runs by impedance using a Xitron Hydra 4200 device and the bio-impedance spectroscopy method (BIS). These volumes were used to test two methods of patient dry weight determination by impedance, that of Chamney et al., based on Ve/W ratio and that of Lopot et al. Based on VE/VT ratio where W denotes body weight. We recommend the 2nd method, but using a new equation that we have proposed for calculating VT, which is ...
International Journal of Heat and Mass Transfer, 2016
HAL - hal.archives-ouvertes.fr, CCSd - Centre pour la Communication Scientifique Direct. Accueil;... more HAL - hal.archives-ouvertes.fr, CCSd - Centre pour la Communication Scientifique Direct. Accueil; Dépôt: S&#x27;authentifier; S&#x27;inscrire. Consultation: Par domaine; Les 30 derniers dépôts; Par année de publication, rédaction, dépôt; Par type de publication; Par collection; Les portails de l&#x27;archive ouverte HAL; Par établissement (extraction automatique); ArXiv; Les Thèses (TEL). Recherche: Recherche simple; Recherche avancée; Accès par identifiant; Les Thèses ...
The purpose of the work presented this paper is to design a model to study experimentally and num... more The purpose of the work presented this paper is to design a model to study experimentally and numerically a micro-Couette blood flow to obtain a constant and controlled shear rate that is a suitable environment for analysis of Red Blood Cell (RBC) aggregation. Due to the simplicity of the flow conditions, aggregate size can be related to the constant shear rate applied. This Couette flow is created by the motion of a second fluid that entrains the blood. The experimental work is coupled with 3D numerical simulations performed using a research computational fluid dynamics solver, Nek5000, based on the spectral element method, while the experiments are conducted using a micro-particle image velocimetry system. Two models of microchannels, with different dimensions, 150 × 33μm and 170 × 64μm, are fabricated in the laboratory using standard photolithography methods. The design of the channel is based on several parameters determined by the simulations. A Newtonian model is tested numeri...
Journal of Visualized Experiments, 2015
2008 5th IEEE International Symposium on Biomedical Imaging: From Nano to Macro, 2008
Optical cross-correlation methods have been used to study the motion of red blood cells (RBC) in ... more Optical cross-correlation methods have been used to study the motion of red blood cells (RBC) in the microcirculation. To evaluate the precision of such a method to determine RBC velocity profiles, we developped a computational model of the microscopy image formation. The following steps were undertaken: 1) a mechanical model was used to mimic three dimensional RBC movements in a tubular parabolic flow; 2) at each time step, a synthetic image was built using microscopic image formation equations based on the depth of correlation of RBCs; and 3) the velocity profile was extracted by a cross-correlation algorithm applied to these synthetic images. The estimated maximum velocities extracted from the simulated images were always smaller than velocities found by simulation. Relative errors (4% to 25%) depended on the vessel radius and on the shape of the velocity profile, but not on the hematocrit or on the maximum velocity.
The International journal of artificial organs, 2002
The effect of temporary position changes, sitting up from supine, on extracellular (ECW) and intr... more The effect of temporary position changes, sitting up from supine, on extracellular (ECW) and intracellular (ICW) resistances and fluid volumes calculated from whole body bioimpedance using a Xitron 4200 impedancemeter was investigated on 8 patients during dialysis for a total of 11 tests. It was found that ECW resistance decreased instantaneously by an average of 2.3% when the patient sits up, due to plasma and interstitial fluid shift into the legs which decreases leg resistance, the major contributor to total resistance. This drop in resistance is incorrectly interpreted by the device as an increase in ECW volume which averages 235 ml. But this effect is completely reversible and both ECW resistance and fluid volume rapidly resume their normal course when the patient returns to his initial position. No significant variation in ICW resistance was observed in any of the patients at the position change. We conclude that segmental impedance, which has been proposed to minimize this ar...
Ultrasound in Medicine and Biology, 2007
Power Doppler imaging (PDI) has been shown to be influenced by the wall filter when assessing art... more Power Doppler imaging (PDI) has been shown to be influenced by the wall filter when assessing arterial stenoses. Real-time 3-D Doppler imaging may likely become a widespread practice in the near future, but how the wall filter could affect PDI during the cardiac cycle has not been investigated. The objective of the study was to demonstrate that the wall filter may produce unexpected major signal losses in real-time 3-D PDI. To test our hypothesis, we first validated binary images obtained from analytical simulations with in vitro PDI acquisitions performed in a tube under pulsatile flow conditions. We then simulated PDI images in the presence of a severe stenosis, considering physiological conditions by finite element modeling. Power Doppler imaging simulations revealed important signal losses within the lumen area at different instants of the flow cycle, and there was a very good concordance between measured and predicted PDI binary images in the tube. Our results show that the wall filter may induce severe PDI signal losses that could negatively influence the assessment of vascular stenosis. Clinicians should therefore be aware of this cause of signal loss to properly interpret power Doppler angiographic images.
ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels, 2012
Experimental studies of blood microflows in rectangular biocompatible polymer microchannels measu... more Experimental studies of blood microflows in rectangular biocompatible polymer microchannels measured using micro-particle image velocimetry are reported. The data processing methods, data collection methods, and choice of channel material are demonstrated to impact the velocity profile measurements obtained. Results show that the use of red blood cells as tracer particles creates a large depth of correlation which can approach the size of the vessel itself and decrease the accuracy of the method. It is shown that changing the amount of overlap in the post-processing parameters affects the results by nearly 10%. The velocity profile is studied as a function of the flow rate of the blood, the hematocrit, or percentage of red blood cells, the shape of the channel, and the channel material. The results highlighted here show that the best processing options include pre-processing, the use of fluorescent tracer particles instead of the red blood cells themselves as tracers give a more accurate prediction of the profile, and the use of silicone as the channel material more closely mimics the behavior of physiology. Acrylic biocompatible polymer channels are shown to give a more parabolic profile at lower levels of hematocrit, while silicone biocompatible polymer channels give a velocity profile that looks more like in vivo flow studies.
Journal of Visualized Experiments, 2013
Micro-particle image velocimetry (μPIV) is used to visualize paired images of micro particles see... more Micro-particle image velocimetry (μPIV) is used to visualize paired images of micro particles seeded in blood flows. The images are crosscorrelated to give an accurate velocity profile. A protocol is presented for μPIV measurements of blood flows in microchannels. At the scale of the microcirculation, blood cannot be considered a homogeneous fluid, as it is a suspension of flexible particles suspended in plasma, a Newtonian fluid. Shear rate, maximum velocity, velocity profile shape, and flow rate can be derived from these measurements. Several key parameters such as focal depth, particle concentration, and system compliance, are presented in order to ensure accurate, useful data along with examples and representative results for various hematocrits and flow conditions.
Frontiers in Physiology
Predicting blood microflow in both simple and complex geometries is challenging because of the co... more Predicting blood microflow in both simple and complex geometries is challenging because of the composition and behavior of the blood at microscale. However, characterization of the velocity in microchannels is the key for gaining insights into cellular interactions at the microscale, mechanisms of diseases, and efficacy of therapeutic solutions. Image-based measurement techniques are a subset of methods for measuring the local flow velocity that typically utilize tracer particles for flow visualization. In the most basic form, a high-speed camera and microscope setup are the only requirements for data acquisition; however, the development of image processing algorithms and equipment has made current image-based techniques more sophisticated. This mini review aims to provide a succinct and accessible overview of image-based experimental measurement techniques to characterize the velocity field of blood microflow. The following techniques are introduced: cell tracking velocimetry, kym...
Lab on a Chip, 2019
A one-mask microfabrication process to build artificial vascular networks for the analysis of blo... more A one-mask microfabrication process to build artificial vascular networks for the analysis of blood flows and hemophysics.
The Journal of the Acoustical Society of America, 2021
Chinchilla et al. Although quantitative ultrasound techniques based on the parameterization of th... more Chinchilla et al. Although quantitative ultrasound techniques based on the parameterization of the backscatter coefficient (BSC) have been successfully applied to blood characterization, theoretical scattering models assume blood as an isotropic scattering medium. However, the red blood cell (RBC) aggregates form anisotropic structures such as rouleaux. The present study proposes an anisotropic formulation of the Effective Medium Theory combined with the Local Monodisperse Approximation (EMTLMA) that considers perfectly aligned prolate-shaped aggregates. Theoretical BSC predictions were first compared with computer simulations of BSCs in a forward problem framework. Computer simulations were conducted for perfectly aligned prolate-shaped aggregates and more complex configurations with partially aligned prolate-shaped aggregates for which the size and orientation of RBC aggregates were obtained from blood optical observations. The isotropic and anisotropic EMTLMA models were then compared in an inverse problem framework to estimate blindly the structural parameters of RBC aggregates from the simulated BSCs. When considering the isotropic EMTLMA, the use of averaged BSCs over different insonification directions significantly improves the estimation of aggregate structural parameters. Overall, the anisotropic EMTLMA was found to be superior to the isotropic EMTLMA in estimating the scatterer volume distribution. These results contribute to a better interpretation of scatterer size estimates for blood characterization.
2017 IEEE International Symposium on Medical Measurements and Applications (MeMeA), 2017
We have designed and fabricated a biomicroviscometer platform for measurement of microflows of bi... more We have designed and fabricated a biomicroviscometer platform for measurement of microflows of biological fluids. The biomicroviscometer combines an optically clear biocompatible polydimethylsiloxane (PDMS) channel with on-chip integrated microfluidic differential pressure sensors and capabilities of modular channel geometries. This setup allows for a direct measurement of the change in pressure and flow rate, increasing the overall accuracy of the measurement of viscosity and optical observation. We present an introduction of this combined method of measurement with different channel dimensions, using Newtonian and non-Newtonian fluids, and the corresponding calculations. This measurement technique has potential applications in measuring rheological properties at the micro level to further blood disease analysis, and lab-on-a-chip fabrication and analysis.
Stenosis or incompetence at severe levels reduce the performance of the heart and place additiona... more Stenosis or incompetence at severe levels reduce the performance of the heart and place additional stress and strain upon it. Therefore, in many cases, surgical replacement of the diseased valve with a Bioprosthetic or Mechanical Heart Valves (MHV) is necessary to restore valve function. Although the lifelong anticoagulant medication and the possible clinical complications (e.g. blood elements damage and/or thrombus formation), Bileaflet MHV are the most implanted valves with over 170,000 implants worldwide each year as a result of high durability and appropriate characteristics for blood hemodynamics (in terms of low pressure gradient and low shear stress level)[1]. Unfortunately, in some cases, Thromboembolic complications and/or pannus formation are possible after Bileaflet valve implantation. The mortality percentage for the reoperation might be as high as 69%. By the way, even though the low percentage of the deficiency in one or both leaflets(0.2%-6% per patient-year), the dan...
This work aims to develop a method to quantitatively analyze red blood cell (RBC) aggregates unde... more This work aims to develop a method to quantitatively analyze red blood cell (RBC) aggregates under controlled flow conditions, based on image processing. The set up consists of RBC suspensions entrained by a second fluid in a 150x33 μm microchannel. The experiments are performed by varying the hematocrit (10, 15 & 20%) and the flow rate (Q=5 & 10 μl/hr). The flow is visualized using a high speed camera coupled to a micro Particle Image Velocimetry (μPIV) system. Videos obtained with the high speed camera are processed using a MATLAB program to detect RBC aggregates based on the images intensities. An average aggregate size has been determined for each of the shear rates and hematocrits. The aggregates are shown to be larger at low flow rates and high hematocrits.
Medical Engineering & Physics, 2019
The wall adhesion of 1 µm microparticles in human blood was studied in circular microchannels. Th... more The wall adhesion of 1 µm microparticles in human blood was studied in circular microchannels. The level of particle wall adhesion was measured for varying levels of shear rate and varying degrees of red blood cell aggregation, which was modulated by the addition of macromolecule dextran 500. The blood preparations were injected into PDMS microfluidic devices that were modified to have circular channels, better matching the geometry of physiological microcirculation compared to square channels or Couette flow systems. The circular walls of the microchannels were embedded with biotinylated phospholipids to which marginating microspheres coated with streptavidin bound. The particle wall adhesion was evaluated by counting the particles that adhered to the channel's wall after flushing the channel. Blood preparations of five dextran concentrations (including baseline case of 0%) were tested for four flow velocities, to quantify the effects of aggregation for varying shear rate. It was found that the level of particle wall adhesion was positively correlated with the level of RBC aggregation, particularly at low shear rates, when aggregation was enhanced. The particle adhesion was especially enhanced at aggregation levels in the range of physiological aggregation levels of whole blood, suggesting that RBC aggregation plays an important role in the dynamics of platelets and leukocytes in vivo.
International Journal of Molecular Sciences
Patients with sickle cell disease (SCD) have poorly deformable red blood cells (RBC) that may imp... more Patients with sickle cell disease (SCD) have poorly deformable red blood cells (RBC) that may impede blood flow into microcirculation. Very few studies have been able to directly visualize microcirculation in humans with SCD. Sublingual video microscopy was performed in eight healthy (HbAA genotype) and four sickle cell individuals (HbSS genotype). Their hematocrit, blood viscosity, red blood cell deformability, and aggregation were individually determined through blood sample collections. Their microcirculation morphology (vessel density and diameter) and microcirculation hemodynamics (local velocity, local viscosity, and local red blood cell deformability) were investigated. The De Backer score was higher (15.9 mm−1) in HbSS individuals compared to HbAA individuals (11.1 mm−1). RBC deformability, derived from their local hemodynamic condition, was lower in HbSS individuals compared to HbAA individuals for vessels < 20 μm. Despite the presence of more rigid RBCs in HbSS individu...
PLOS ONE
Red blood cells (RBCs) are the most abundant cells in human blood. Remarkably RBCs deform and bri... more Red blood cells (RBCs) are the most abundant cells in human blood. Remarkably RBCs deform and bridge together to form aggregates under very low shear rates. The theory and mechanics behind aggregation are, however, not yet completely understood. The main objective of this work is to quantify and characterize RBC aggregates in order to enhance the current understanding of the non-Newtonian behaviour of blood in microcirculation. Suspensions of human blood were flowed and observed in vitro in poly-di-methyl-siloxane (PDMS) microchannels to characterize RBC aggregates. These microchannels were fabricated using standard photolithography methods. Experiments were performed using a micro particle image velocimetry (μPIV) system for shear rate measurements, coupled with a high-speed camera for flow visualization. RBC aggregate sizes were quantified in controlled and measurable shear rate environments for 5, 10 and 15% hematocrit. Aggregate sizes were determined using image processing techniques, while apparent viscosity was measured using optical viscometry. For the samples suspended at 5% H, aggregate size was not strongly correlated with shear rate. For the 10% H suspensions, in contrast, lowering the shear rate below 10 s-1 resulted in a significant increase of RBC aggregate sizes. The viscosity was found to increase with decreasing shear rate and increasing hematocrit, exemplifying the established non-Newtonian shear-thinning behaviour of blood. Increase in aggregation size did not translate into a linear increase of the blood viscosity. Temperature was shown to affect blood viscosity as expected, however, no correlation for aggregate size with temperature was observed. Non-Newtonian parameters associated with power law and Carreau models were determined by fitting the experimental data and can be used towards the simple modeling of blood's non-Newtonian behaviour in microcirculation. This work establishes a relationship between RBC aggregate sizes and corresponding shear rates and one between RBC aggregate sizes and apparent blood viscosity at body and room temperatures, in a microfluidic environment for low hematocrit. Effects of hematocrit, shear rate, viscosity and temperature on RBC aggregate sizes have been quantified.
International Journal of Heat and Mass Transfer, 2016
Itbm Rbm, Oct 1, 2004
We have measured extracellular (VE) and total water (VT) volumes in 17 dialysed patients for a to... more We have measured extracellular (VE) and total water (VT) volumes in 17 dialysed patients for a total of 46 runs by impedance using a Xitron Hydra 4200 device and the bio-impedance spectroscopy method (BIS). These volumes were used to test two methods of patient dry weight determination by impedance, that of Chamney et al., based on Ve/W ratio and that of Lopot et al. Based on VE/VT ratio where W denotes body weight. We recommend the 2nd method, but using a new equation that we have proposed for calculating VT, which is ...
International Journal of Heat and Mass Transfer, 2016
HAL - hal.archives-ouvertes.fr, CCSd - Centre pour la Communication Scientifique Direct. Accueil;... more HAL - hal.archives-ouvertes.fr, CCSd - Centre pour la Communication Scientifique Direct. Accueil; Dépôt: S&#x27;authentifier; S&#x27;inscrire. Consultation: Par domaine; Les 30 derniers dépôts; Par année de publication, rédaction, dépôt; Par type de publication; Par collection; Les portails de l&#x27;archive ouverte HAL; Par établissement (extraction automatique); ArXiv; Les Thèses (TEL). Recherche: Recherche simple; Recherche avancée; Accès par identifiant; Les Thèses ...
The purpose of the work presented this paper is to design a model to study experimentally and num... more The purpose of the work presented this paper is to design a model to study experimentally and numerically a micro-Couette blood flow to obtain a constant and controlled shear rate that is a suitable environment for analysis of Red Blood Cell (RBC) aggregation. Due to the simplicity of the flow conditions, aggregate size can be related to the constant shear rate applied. This Couette flow is created by the motion of a second fluid that entrains the blood. The experimental work is coupled with 3D numerical simulations performed using a research computational fluid dynamics solver, Nek5000, based on the spectral element method, while the experiments are conducted using a micro-particle image velocimetry system. Two models of microchannels, with different dimensions, 150 × 33μm and 170 × 64μm, are fabricated in the laboratory using standard photolithography methods. The design of the channel is based on several parameters determined by the simulations. A Newtonian model is tested numeri...
Journal of Visualized Experiments, 2015
2008 5th IEEE International Symposium on Biomedical Imaging: From Nano to Macro, 2008
Optical cross-correlation methods have been used to study the motion of red blood cells (RBC) in ... more Optical cross-correlation methods have been used to study the motion of red blood cells (RBC) in the microcirculation. To evaluate the precision of such a method to determine RBC velocity profiles, we developped a computational model of the microscopy image formation. The following steps were undertaken: 1) a mechanical model was used to mimic three dimensional RBC movements in a tubular parabolic flow; 2) at each time step, a synthetic image was built using microscopic image formation equations based on the depth of correlation of RBCs; and 3) the velocity profile was extracted by a cross-correlation algorithm applied to these synthetic images. The estimated maximum velocities extracted from the simulated images were always smaller than velocities found by simulation. Relative errors (4% to 25%) depended on the vessel radius and on the shape of the velocity profile, but not on the hematocrit or on the maximum velocity.
The International journal of artificial organs, 2002
The effect of temporary position changes, sitting up from supine, on extracellular (ECW) and intr... more The effect of temporary position changes, sitting up from supine, on extracellular (ECW) and intracellular (ICW) resistances and fluid volumes calculated from whole body bioimpedance using a Xitron 4200 impedancemeter was investigated on 8 patients during dialysis for a total of 11 tests. It was found that ECW resistance decreased instantaneously by an average of 2.3% when the patient sits up, due to plasma and interstitial fluid shift into the legs which decreases leg resistance, the major contributor to total resistance. This drop in resistance is incorrectly interpreted by the device as an increase in ECW volume which averages 235 ml. But this effect is completely reversible and both ECW resistance and fluid volume rapidly resume their normal course when the patient returns to his initial position. No significant variation in ICW resistance was observed in any of the patients at the position change. We conclude that segmental impedance, which has been proposed to minimize this ar...
Ultrasound in Medicine and Biology, 2007
Power Doppler imaging (PDI) has been shown to be influenced by the wall filter when assessing art... more Power Doppler imaging (PDI) has been shown to be influenced by the wall filter when assessing arterial stenoses. Real-time 3-D Doppler imaging may likely become a widespread practice in the near future, but how the wall filter could affect PDI during the cardiac cycle has not been investigated. The objective of the study was to demonstrate that the wall filter may produce unexpected major signal losses in real-time 3-D PDI. To test our hypothesis, we first validated binary images obtained from analytical simulations with in vitro PDI acquisitions performed in a tube under pulsatile flow conditions. We then simulated PDI images in the presence of a severe stenosis, considering physiological conditions by finite element modeling. Power Doppler imaging simulations revealed important signal losses within the lumen area at different instants of the flow cycle, and there was a very good concordance between measured and predicted PDI binary images in the tube. Our results show that the wall filter may induce severe PDI signal losses that could negatively influence the assessment of vascular stenosis. Clinicians should therefore be aware of this cause of signal loss to properly interpret power Doppler angiographic images.
ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels, 2012
Experimental studies of blood microflows in rectangular biocompatible polymer microchannels measu... more Experimental studies of blood microflows in rectangular biocompatible polymer microchannels measured using micro-particle image velocimetry are reported. The data processing methods, data collection methods, and choice of channel material are demonstrated to impact the velocity profile measurements obtained. Results show that the use of red blood cells as tracer particles creates a large depth of correlation which can approach the size of the vessel itself and decrease the accuracy of the method. It is shown that changing the amount of overlap in the post-processing parameters affects the results by nearly 10%. The velocity profile is studied as a function of the flow rate of the blood, the hematocrit, or percentage of red blood cells, the shape of the channel, and the channel material. The results highlighted here show that the best processing options include pre-processing, the use of fluorescent tracer particles instead of the red blood cells themselves as tracers give a more accurate prediction of the profile, and the use of silicone as the channel material more closely mimics the behavior of physiology. Acrylic biocompatible polymer channels are shown to give a more parabolic profile at lower levels of hematocrit, while silicone biocompatible polymer channels give a velocity profile that looks more like in vivo flow studies.
Journal of Visualized Experiments, 2013
Micro-particle image velocimetry (μPIV) is used to visualize paired images of micro particles see... more Micro-particle image velocimetry (μPIV) is used to visualize paired images of micro particles seeded in blood flows. The images are crosscorrelated to give an accurate velocity profile. A protocol is presented for μPIV measurements of blood flows in microchannels. At the scale of the microcirculation, blood cannot be considered a homogeneous fluid, as it is a suspension of flexible particles suspended in plasma, a Newtonian fluid. Shear rate, maximum velocity, velocity profile shape, and flow rate can be derived from these measurements. Several key parameters such as focal depth, particle concentration, and system compliance, are presented in order to ensure accurate, useful data along with examples and representative results for various hematocrits and flow conditions.