Stress Analysis of Aortic Vessels under Stent Graft / 医用生物力学

Objective To simulate the interaction between the stent graft (SG) and the aortic wall with finite element (FE) analysis by considering the influence of residual stress field, so as to study the stent influence on stress distributions of the aortic wall. Methods The three-dimensional (3D) residual stress field was generated in an idealized bi-layered thick-wall aortic model via a stress-driven anisotropic growth model by reducing the transmural stress gradient. Upon virtually deploying the SG, the stress on the aortic wall was calculated. Results The 3D residual stress field, corresponding to an opening angle of 117.5°, was shown to reduce the transmural stress gradient in both the circumferential and axial directions. The maximum stress was found at the contact area between aortic wall and wave peak of the stent. At 20% oversize ratio of the stent, the maximum stresses on the aortic wall in circumferential and axial direction were 412 and 132 kPa, respectively, while the in-plane shear stresses σrθ and σrz were both 78 kPa. Under residual stress, the maximum radial, circumferential and axial stresses were decreased by 14.9%, 40.5% and 33.8%, respectively, while the maximum shear stresses σrθ ，σrz，σθz were reduced by 2.5%, 7.1% and 27%, respectively. With the increase of oversize ratio from 10% to 20%, the maximum radial, circumferential and axial stresses were increased by 316%, 129% and 41%, respectively, while the maximum shear stresses σrθ ，σrz，σθz were increased by 661%, 450% and 466%, respectively. Conclusions The residual stress can effectively reduce the transmural stress gradient. Both the residual stress and the oversize ratio of the stent play an important role in modulating the wall stress distribution and the maximum stress.

Reoperation for Rupture of the Porcine Aortic Wall of a Stentless Bioprosthesis / 日本心臓血管外科学会雑誌

A 63-year-old woman presented with pseudoaneurysm formation due to rupture of the porcine aortic wall of the stentless bioprosthesis. She had undergone aortic root replacement using the full root technique with the 25-mm Prima Plus bioprosthesis for annuloaortic ectasia. Congestive heart failure, appearing 65 months after the first surgery, progressed rapidly. Multidetector computed tomography (CT) showed a pseudoaneurysm of the aortic root, and echocardiography revealed severe mitral regurgitation. At reoperation, a large pseudoaneurysm with a 20-mm horizontal tear was seen in the non-coronary sinus of the Prima Plus valve. A repeat aortic root replacement and mitral valve replacement with two mechanical valves were performed. The patient had an uneventful recovery. Histologic examination of the explanted porcine aortic root showed host mononuclear cells and macrophages between the well-stained and poorly stained areas, suggesting that the torn tissue had undergone host-mediated degeneration to some extent. Porcine aortic roots have excellent hemodynamic features, but ruptures in the aortic sinuses of the porcine aortic root have been reported in some cases. Careful follow up with CT or echocardiography is therefore needed after aortic root replacement with stentless bioprostheses.

Morphological Type and Histological Features of the Dilated Ascending Aorta in Patients with a Bicuspid Aortic Valve / 日本心臓血管外科学会雑誌

Bicuspid aortic valve (BAV) is one of the more common congenital anomalies. It is well known that the ascending aorta and aortic root sometimes dilate in patients with BAV, even when the valve function is normal. We examined the morphological type and histological features of the dilated ascending aorta in patients with BAV. Of 276 patients who underwent aortic valve replacement (including coronary artery bypass grafting) from 2004 onwards, 60 (21.5%) with BAV were included in this study. The type of BAV was defined according to the Sievers classification. Type 1 BAV was the most common, and enlargement of the ascending aorta (≥45 mm) was the most common in the L/R type of BAV (48%). The morphology of the dilated ascending aortic wall was evaluated using three-dimensional CT angiography. The majority of dilations were asymmetric, but dilation was symmetric in the patient with dilation of the aortic root. Histological examination graded cystic medial necrosis of the ascending aortic walls using the aortic wall score. All patients with BAV had degeneration of the aortic wall, even when there was no dilation. The aortic walls of patients with dilated aortic roots showed advanced degeneration compared with the aortic walls of other patients. Therefore, aggressive root replacement may be appropriate, when the root is mildly dilated in patient with BAV.

Structure of the aortic wall in the guinea pig and rat

The segmental microscopic architecture of the aortic wall of guinea pigs and albino rats was studied at the thoracicascending (T2-3), thoracic descending (T6-7) and abdominal infrarenal (L5-6) levels. Variables such as layer thickness,the number of elastic lamellae in the medial layer, and the diameter of the aortic segments were analyzedhistomorphometrically. The aortic wall of both species showed the usual elastic pattern, although variable amounts ofelastic lamellae, collagen fibers and smooth muscle cells were observed in the segmental analyses. A marked reductionin the number of elastic lamellae in the medial layer and in vascular diameter was observed in the abdominal aorticsegment of both species. Intimal folds, a gradual decrease in elastic lamellae from the ascending to the aorta abdominalaorta and a meshwork of adventitial collagen fibers and elastic lamellae were observed. These data indicate that thereare small but significant segmental variations in the aortic wall of these two species.

Development of elastin layers in the aortic wall of human fetuses

The presence of elastin layers in the aortic walls of twelve human fetuses was confirmed with scanning electron microscope pictures after hot alkali treatment and histochemical examination. In addition, the number of elastin layers in aortic walls of 5 different segments were compared in fetuses of varying ages. Aldehyde fuchsin stained slides of elastin ascending aortas showed a range between 27 and 55 layers of elastin in fetuses of 8 weeks to 32 weeks. However, in the lower abdominal aortas, elastin layers decreased from 28 to only 3 layers for fetuses of the same age. Furthermore, as elastin layers decreased from ascending aorta to abdominal aorta with the progression of fetal life, similar changes in the elastin lamellae were observed. These results suggest that while aortas grow rapidly in length, the medial elastin thickens slowly, perhaps due to slow development of hydrodynamic forces and pressures. Also the adventitial elastin appears to lose out gradually along the length from ascending aorta to abdominal aorta.

Effect of Pollen Compound Tablets on Atherosclerosis in Rabbits / 昆明医科大学学报

An experimental atherosclerotic model was established by feeding rabbits with 0.5 gram cholesterol every day.17 rabbits were divided by random pairing in to two groups, one feeding with pollen compound tablets in addition but the other not. The preventive effect of pollen compound tablets on the development of atherosclerosis was evaluated. The results showed that the cholesterol level in the aortic wall, the surface area of the aortic atherosclerotic lesions and its severity, and the frequency and severity of the coronary arterial lesions were diminished markedly in the rabbits fed with pollen compound tablets. The results also indicated that this anti-atherosclerosis effect was related to the decrease of lipids, apoipoprotein B and peroxide lipids in serum and the inhibition of the platelet aggregation rate. It also related to the increase of prostacyclin in serum.