RESUMEN
When simulating blood flow in intracranial aneurysms (IAs), the Newtonian model seems to be ubiquitous. However, analyzing the results from the few studies on this subject, the doubt remains on whether it is necessary to use non-Newtonian models in computational fluid dynamics (CFD) simulations of cerebral vascular flows. The objective of this study is to investigate whether different rheology models would influence the hemodynamic parameters related to the wall shear stress (WSS) for ruptured and unruptured IA cases, especially because ruptured aneurysms normally have morphological features, such as lobular regions and blebs, that could trigger non-Newtonian phenomena in the blood flow due to low shear rates. Using CFD in an open-source framework, we simulated four ruptured and four unruptured patient-specific aneurysms to assess the influence of the blood modeling on the main hemodynamic variables associated with aneurysm formation, growth, and rupture. Results for WSS and oscillatory shear index (OSI) and their metrics were obtained using Casson and Carreau-Yasuda non-Newtonian models and were compared with those obtained using the Newtonian model. We found that all differences between non-Newtonian and the Newtonian models were consistent among all cases irrespective of their rupture status. We further found that the WSS at peak systole is overestimated by more than 50% by using the non-Newtonian models, but its metrics based on time and surface averaged values are less affected-the maximum relative difference among the cases is 7% for the Casson model. On the other hand, the surface-averaged OSI is underestimated by more than 30% by the non-Newtonian models. These results suggest that it is recommended to investigate different blood rheology models in IAs simulations when specific parameters to characterize the flow are needed, such as peak-systole WSS and OSI.
Asunto(s)
Aneurisma IntracranealRESUMEN
The aim of the present study was to test the effects of Pfaffia paniculata (PP) extract on the red blood cell (RBC) rheological properties of patients with sickle cell disease (SCD) and healthy (AA) individuals. Blood from 7 SCD and 4 AA individuals were collected in EDTA tubes. Washed RBCs were incubated with various concentration of PP extract: 0.0, 0.2 or 0.5âmg/ml of PP solution for 5âhrs at 37°C. RBC deformability was measured by ektacytometry at 9 shear stresses ranging from 0.3 to 30âPa, and RBC aggregation properties were determined by laser-backscattered techniques. Because RBCs from SCD patients are fragile, a stability test was also performed to test for the fragility of RBC exposed to a constant shear stress (70âPa) for 10âmin. While RBC deformability was not improved by the use of PP extract in AA, we noted an improvement of this parameter in patients with SCD between the 0.0 and 0.5âmg/ml conditions. In contrast to AA RBCs, the fragility of SCD RBCs was not affected by PP extract. In conclusion, this study demonstrates the beneficial effects, in-vitro, of PP extract on the RBC deformability of SCD patients, notably at high shear stress (a shear stress condition usually found in capillaries).
Asunto(s)
Anemia de Células Falciformes/sangre , Deformación Eritrocítica/efectos de los fármacos , Eritrocitos/efectos de los fármacos , Extractos Vegetales/uso terapéutico , Reología , Femenino , Humanos , MasculinoRESUMEN
Sleep apnea patients and obese subjects are overexposed to cardiovascular diseases. These two health conditions may be associated with hemorheological alterations which could increase the cardiovascular risk. The present study investigated the hemorheological characteristics in patients with overweight and/or sleep apnea to identify the main predictor of red blood cell (RBC) abnormalities in sleep apnea patients. Ninety-seven patients were subjected to one night sleep polygraphy to determine their sleep apnea status. Body mass index (BMI) and the apnea/hypopnea index (AHI) were determined for categorization of obesity and sleep apnea status. Blood was sampled for hematocrit, blood viscosity, RBC deformability, aggregation and disaggregation threshold measurements. BMI and AHI were positively associated and were both positively associated with RBC aggregation. Analyses of covariance and multiple regression analyses revealed that BMI was more predictive of RBC aggregation than AHI. No association of BMI classes and AHI classes with RBC deformability or blood viscosity was observed. This study shows that increased RBC aggregation in sleep apnea patients is caused by overweight. Therapies to improve blood rheology in sleep apnea patients, and therefore reduce the risk for cardiovascular disorders, should focus on weight-loss.
Asunto(s)
Agregación Eritrocitaria , Sobrepeso/complicaciones , Apnea Obstructiva del Sueño/sangre , Apnea Obstructiva del Sueño/complicaciones , Viscosidad Sanguínea , Índice de Masa Corporal , Enfermedades Cardiovasculares/etiología , Femenino , Hematócrito , Humanos , Masculino , Persona de Mediana Edad , Sobrepeso/sangre , Sobrepeso/patología , Factores de RiesgoRESUMEN
Vascular function has been found to be impaired in patients with sickle cell disease (SCD). The present study investigated the determinants of systemic vascular resistance in two main SCD syndromes in children: sickle cell anemia (SCA) and sickle cell-hemoglobin C disease (SCC). Nitric oxide metabolites (NOx), hematological, hemorheological, and hemodynamical parameters were investigated in 61 children with SCA and 49 children with SCC. While mean arterial pressure was not different between SCA and SCC children, systemic vascular resistance (SVR) was greater in SCC children. Although SVR and blood viscosity (ηb) were not correlated in SCC children, the increase of ηb (+18%) in SCC children compared to SCA children results in a greater mean SVR in this former group. SVR was positively correlated with ηb, hemoglobin (Hb) level and RBC deformability, and negatively with NOx level in SCA children. Multivariate linear regression model showed that both NOx and Hb levels were independently associated with SVR in SCA children. In SCC children, only NOx level was associated with SVR. In conclusion, vascular function of SCC children seems to better cope with higher ηb compared to SCA children. Since the occurrence of vaso-occlusive like complications are less frequent in SCC than in SCA children, this finding suggests a pathophysiological link between the vascular function alteration and these clinical manifestations. In addition, our results suggested that nitric oxide metabolism plays a key role in the regulation of SVR, both in SCA and SCC.