Hemodynamic Study on Non-Newtonian Properties of Fontan Procedure / 医用生物力学

Objective To investigate the effects of non-Newtonian properties on hemodynamic characteristics of Fontan procedure in computational simulation. Methods A Fontan vascular model was reconstructed based on patient-specific medical images. The boundary conditions were set according to velocity profiles measured by real-time echocardiography. The Newtonian model and two non-Newtonian (Casson and Carreau) models were applied to analyze the hemodynamic parameters, including flow ratio (FR), energy loss (EL), wall shear stress (WSS) as well as non-Newtonian importance factor, so as to compare flow differences between the Newtonian model and non-Newtonian models. Results The rheological models had small effects on the FR. The EL of non-Newtonian models was higher than that of the Newtonian model, and the EL of Casson model was the highest. Flow recirculation and flow disturbance accompanied with low WSS were observed in inferior vena cava (IVC). At low inflow velocity, flow disturbance in IVC of Newtonian model was more obvious. The calculations of non-Newtonian importance factor suggested significant non-Newtonian viscosity in IVC. Conclusions Non-Newtonian viscosity is significant in IVC where low velocity and flow recirculation are observed. Non-Newtonian properties of the blood should be considered in patient-specific hemodynamic simulation of Fontan procedure.

Analysis on Hemodynamic Characteristics of Individualized Carotid Aneurysms / 医用生物力学

Objective To construct an individualized fluid-solid coupling model, calculate and analyze the influence of different blood characteristics on hemodynamics in the aneurysm cavity, and further explore the influence on rupture of the cerebral aneurysm. Methods First, three-dimensional (3D) digital silhouette images were collected to construct an aneurysm model, and the influence of different blood flow characteristics on dynamic parameters of the carotid aneurysm was analyzed by computational fluid dynamic (CFD) method under the same boundary conditions. Finally, particle image velocimetry (PIV) experiment was performed on the simplified carotid aneurysm experimental model to verify reliability of the blood flow calculation method. Results For the fluid-structure coupling model with different blood flow characteristics, within a cardiac cycle, at the same time, obvious differences were found in the low velocity area of tumor cavity, the streamline distributions of tumor cavity, the wall shear stress (WSS) and deformation of the aneurysm wall. Through PIV experiments, it was found that the vortex position in tumor cavity changed with the velocity, which was consistent with flow trend of the simulation analysis results. Conclusions The two kinds of blood characteristics have small differences, but the non-Newtonian fluid is closer to true state of the blood, and the numerical results will be closer to true flow state.

Polymeric emulgel carrying Cinnamomum tamala extract: promising delivery system for potential topical applications

Currently, the use of natural compounds obtained from plants tremendously increased due to their promising therapeutic properties. The aim of this study was to formulate a stable emulgel formulation loaded with Cinnamomum tamala (CT) extract. The antioxidant activity of plant extract was determined by DPPH inhibition assay. The extract was successfully loaded into an emulgels using different concentrations of carbopol-940, liquid paraffin, emulsifying agents and preservatives. Preliminary stability study was performed of 17 CT emulgel formulations at accelerated temperature of 50 °C for 2-months. Organoleptic evaluation, centrifugation, globule size, pH, electrical conductivity and rheological studies were performed for a period of 90-days at different temperature including 8, 25, 40 and 40 °C ±75% RH. The CT extract showed promising antioxidant activity of about 81%. On the other hand, the CT loaded emulgel formulation displayed high physical stability at all tested conditions of temperature and time. However, slight decrease in pH and minimum increase in conductivity was observed at 40 and 40 °C±75% RH. The rheological examination of CT emulgel indicated the flow index values of all the samples kept at different temperatures were less than 1, demonstrated non-newtonian and pseudo-plastic nature of CT emulgel. Taken together, the CT emulgel formulation has been evinced to be an excellent addition in the field of topical formulations.

Patient-Specific Computational Fluid Dynamics in Ruptured Posterior Communicating Aneurysms Using Measured Non-Newtonian Viscosity : A Preliminary Study

OBJECTIVE: The objective of this study was to analyze patient-specific blood flow in ruptured aneurysms using obtained non-Newtonian viscosity and to observe associated hemodynamic features and morphological effects.METHODS: Five patients with acute subarachnoid hemorrhage caused by ruptured posterior communicating artery aneurysms were included in the study. Patients’ blood samples were measured immediately after enrollment. Computational fluid dynamics (CFD) was conducted to evaluate viscosity distributions and wall shear stress (WSS) distributions using a patient-specific geometric model and shear-thinning viscosity properties.RESULTS: Substantial viscosity change was found at the dome of the aneurysms studied when applying non-Newtonian blood viscosity measured at peak-systole and end-diastole. The maximal WSS of the non-Newtonian model on an aneurysm at peaksystole was approximately 16% lower compared to Newtonian fluid, and most of the hemodynamic features of Newtonian flow at the aneurysms were higher, except for minimal WSS value. However, the differences between the Newtonian and non-Newtonian flow were not statistically significant. Rupture point of an aneurysm showed low WSS regardless of Newtonian or non-Newtonian CFD analyses.CONCLUSION: By using measured non-Newtonian viscosity and geometry on patient-specific CFD analysis, morphologic differences in hemodynamic features, such as changes in whole blood viscosity and WSS, were observed. Therefore, measured non-Newtonian viscosity might be possibly useful to obtain patient-specific hemodynamic and morphologic result.

Patient-Specific Computational Fluid Dynamics in Ruptured Posterior Communicating Aneurysms Using Measured Non-Newtonian Viscosity : A Preliminary Study

OBJECTIVE: The objective of this study was to analyze patient-specific blood flow in ruptured aneurysms using obtained non-Newtonian viscosity and to observe associated hemodynamic features and morphological effects. METHODS: Five patients with acute subarachnoid hemorrhage caused by ruptured posterior communicating artery aneurysms were included in the study. Patients’ blood samples were measured immediately after enrollment. Computational fluid dynamics (CFD) was conducted to evaluate viscosity distributions and wall shear stress (WSS) distributions using a patient-specific geometric model and shear-thinning viscosity properties. RESULTS: Substantial viscosity change was found at the dome of the aneurysms studied when applying non-Newtonian blood viscosity measured at peak-systole and end-diastole. The maximal WSS of the non-Newtonian model on an aneurysm at peaksystole was approximately 16% lower compared to Newtonian fluid, and most of the hemodynamic features of Newtonian flow at the aneurysms were higher, except for minimal WSS value. However, the differences between the Newtonian and non-Newtonian flow were not statistically significant. Rupture point of an aneurysm showed low WSS regardless of Newtonian or non-Newtonian CFD analyses. CONCLUSION: By using measured non-Newtonian viscosity and geometry on patient-specific CFD analysis, morphologic differences in hemodynamic features, such as changes in whole blood viscosity and WSS, were observed. Therefore, measured non-Newtonian viscosity might be possibly useful to obtain patient-specific hemodynamic and morphologic result.

Modelo matemático simplificado para determinar a capacidade erosiva de um escoamento lamoso em regime laminar pulsante / A simplified mathematical model to estimate the erosive capacity of a pulsating laminar muddy flow

RESUMO Neste artigo foi proposto um modelo matemático simplificado para inferir sobre a capacidade erosiva de um escoamento lamoso em regime laminar com presença de roll waves (efeito pulsante) na superfície livre. Na perspectiva de aplicação de resultados no contexto de desastres naturais (corridas de lama), foi determinada a evolução da velocidade média e da tensão de cisalhamento no fundo do canal. O modelo proposto é baseado nas equações de águas rasas e na reologia de Herschel-Bulkley, como representativa das lamas. A validação e a aplicação do modelo foram feitas a partir de dados experimentais de roll waves geradas em canal no laboratório confrontados com resultados de simulações numéricas. Os resultados obtidos mostram um incremento na capacidade erosiva, na presença de roll waves, da ordem de 12% em relação ao escoamento base, valor este em concordância com os 10% apontados por Ng e Mei (1994) para uma reologia mais simplificada.

ABSTRACT In this paper, we proposed and validated a simplified mathematical model to estimate the erosive capacity of a muddy laminar flow with roll waves (pulsating effect) on the free surface. From the perspective of applying results in the context of natural disasters (mudflows), the evolution of mean velocity and bottom shear stress in the channel were determined. The proposed model is based on shallow water equations and Herschel-Bulkley rheology as representative of the muds. The model was validated by comparison with results of numerical simulations and experimental data of roll waves generated in a channel. In-depth comparative analyses were made for inferring the erosive capacity of this sort of flow. The obtained results show an increase of erosive capacity (12%) due to the presence of roll waves in relation to the uniform flow's. Similar values (10%) were found by Ng and Mei (1994) for a more simplified rheology model.