Numerical Simulation of Blood Flow in Aorta with Dilation:A Comparison between Laminar and LES Modeling Methods

Computational modeling methods have been increasingly employed to quantify aortic hemodynamic parameters that are challenging to in vivo measurements but important for the diagnosis/treatment of aortic disease.Although the presence of turbulence-like behaviors of blood flow in normal or diseased aorta has long been confirmed,the majority of existing computational model studies adopted the laminar flow assumption(LFA)in the treatment of sub-grid flow variables.So far,it remains unclear whether LFA would significantly compromise the reliability of hemodynamic simulation.In the present study,we addressed the issue in the context of a specific aortopathy,namely aortic dilation,which is usually accompanied by disturbed flow patterns.Three patient-specific aortas with treated/untreated dilation of the ascending segment were investigated,and their geometrical models were reconstructed from computed tomography angiographic images,with the boundary conditions being prescribed based on flow velocity information measured in vivo with the phase contrast magnetic resonance imaging technique.For the modeling of blood flow,apart from the traditional LFA-based method in which sub-grid flow dynamics is ignored,the large eddy simulation(LES)method capable of incorporating the dissipative energy loss induced by turbulent eddies at the sub-grid level,was adopted and taken as a reference for examining the performance of the LFA-based method.Obtained results showed that the simulated large-scale flow patterns with the two methods had high similarity,both agreeing well with in vivo measurements,although locally large between-method discrepancies in computed hemodynamic quantities existed in regions with high intensity of flow turbulence.Quantitatively,a switch from the LES to the LFAbased modeling method led to mild(<6%)changes in computed space-averaged wall shear stress metrics(i.e.,SA-TAWSS,SA-OSI)in the ascending aortic segment where intensive vortex evolution accompanied by high statistical Reynolds stress was observed.In addition,comparisons among the three aortas revealed that the treatment status of aortic dilation or the concomitant presence of aortic valve disease,despite its remarkable influence on flow patterns in the ascending aortic segment,did not significantly affect the degrees of discrepancies between the two modeling methods in predicting SA-TAWSS and SA-OSI.These findings suggest that aortic dilation per se does not induce strong flow turbulence that substantially negates the validity of LFA-based modeling,especially in simulating macro-scale hemodynamic features.

Prenatal Diagnosis of Abnormal Sternum Development and Dilated Aortic Root in a Fetus with a Novel 204 kb Microdeletion of the TGFRB2 Gene

The Loeys-Dietz syndrome (LDS) is a connective tissue disorder that is associated with vascular abnormalities, including aggressive aortic aneurysms, as well as skeletal and craniofacial malformations. The molecular mechanism of this syndrome remains to be fully elucidated. In this case, we describe a 29-year-old woman, gravida 2 para 1, who was referred for consultation after urinary tract malformations were observed during her mid-gestation anatomic survey. Following referral to our unit, ultrasound examination of the 21-week fetus was repeated. The fetus was observed to have a dilated aortic root and a poorly ossified sternum with mild pectus deformity. After elective termination, single nucleotide polymorphism microarray testing identified a novel 204 kb microdeletion involving the short arm of chromosome 3. The deleted genetic material included 4 exons of the TGFBR2 gene. Although the phenotype of LDS may be caused by haploinsufficiency of the TGFBR1 or TGFBR2 gene, our experience suggests a more complex picture of LDS. The study of such cases might further elucidate its pathogenesis.

Retrospective analysis of the prognostic effect of angiotensin receptor blocker on non-Marfan aortic dissection

Background Aortic dissection(AD)is a life-threatening vascular disease caused by various etiologies including Marfan’s syndrome.Angiotensin receptor blocker(ARB)drugs have been confirmed beneficial for patients with Marfanoid AD but remain unclear for non-Marfanoid case.Methods Patients with DeBakey typeⅢ,Standford A aortic dissection were consecutively recruited to Guangdong Provincial People’s Hospital and Jieyang People’s Hospital between January 2010 and January 2015,with 25 individuals in the ARB group and 32 individuals in the non-ARB group(control group),respectively.The follow-up was performed by database or telephone.The follow-up data consisted of patient’s symptoms and chief complaints,blood pressure,heart rate,and aortic computed tomography angiography(CTA)data.Endpoints and in-hospital events were recorded.Results Baseline data,including age,gender,heart rate,smoking status,and the incidence of diabetes,demonstrated no significant difference between two groups.There was neither death nor urgent surgical case in either group during the follow-up period.The aortic CTA follow-up demonstrated the absorption of the proximal inversely avulsed hematoma for both groups,whereas the reduction was more evident in the ARB group as compared with the non-ARB group[-(9.33±1.99)mm vs.-(4.08±2.35)mm,respectively,P<0.05],suggesting that hematoma absorption was more remarkable in the ARB group.The maximum vascular diameter at the dissection in both groups declined during the follow-up,whereas the reduction in the ARB group was significantly more striking relative to that in the non-ARB group[-(5.50±1.15)mm vs.-(0.31±0.69)mm,respectively,P<0.001],indicating a potential role of ARB drugs in curbing aortic enlargement and remodeling.Conclusions Independent of blood pressure(BP)reduction,ARB utilization in patients with non-Marfan’s aortic dissection may facilitate the absorption of reverse-torn hematoma at the proximal end of dissection,as well as delaying the aortic dilation and remodeling.