Does the AVNeo valve reduce wall stress on the aortic wall? A cardiac magnetic resonance analysis with 4D-flow for the evaluation of aortic valve replacement with the Ozaki technique.

OBJECTIVES: Aortic valve neocuspidalization aims to replace the 3 aortic cusps with autologous pericardium pre-treated with glutaraldehyde, and it is a surgical alternative to the classical aortic valve replacement (AVR). Image-based patient-specific computational fluid dynamics allows the derivation of shear stress on the aortic wall [wall shear stress (WSS)]. Previous studies support a potential link between increased WSS and histological alterations of the aortic wall. The aim of this study is to compare the WSS of the ascending aorta in patients undergoing aortic valve neocuspidalization versus AVR with biological prostheses. METHODS: This is a prospective nonrandomized clinical trial. Each patient underwent a 4D-flow cardiac magnetic resonance scan after surgery, which informed patient-specific computational fluid dynamics models to evaluate WSS at the ascending aortic wall. The adjusted variables were calculated by summing the residuals obtained from a multivariate linear model (with ejection fraction and left ventricle outflow tract-aorta angle as covariates) to the mean of the variables. RESULTS: Ten patients treated with aortic valve neocuspidalization were enrolled and compared with 10 AVR patients. The aortic valve neocuspidalization group showed a significantly lower WSS in the outer curvature segments of the proximal and distal ascending aorta as compared to AVR patients (P = 0.0179 and 0.0412, respectively). WSS levels remained significantly lower along the outer curvature of the proximal aorta in the aortic valve neocuspidalization population, even after adjusting the WSS for the ejection fraction and the left ventricle outflow tract-aorta angle [2.44 Pa (2.17-3.01) vs 1.94 Pa (1.72-2.01), P = 0.02]. CONCLUSIONS: Aortic valve neocuspidalization hemodynamical features are potentially associated with a lower WSS in the ascending aorta as compared to commercially available bioprosthetic valves.

The influence of tumour vasculature on fluid flow in solid tumours: a mathematical modelling study.

Tumour vasculature is known to be aberrant, tortuous and erratic which can have significant implications for fluid flow. Fluid dynamics in tumour tissue plays an important part in tumour growth, metastasis and the delivery of therapeutics. Mathematical models are increasingly employed to elucidate the complex interplay between various aspects of the tumour vasculature and fluid flow. Previous models usually assume a uniformly distributed vasculature without explicitly describing its architecture or incorporate the distribution of vasculature without accounting for real geometric features of the network. In this study, an integrated computational model is developed by resolving fluid flow at the single capillary level across the whole tumour vascular network. It consists of an angiogenesis model and a fluid flow model which resolves flow as a function of the explicit vasculature by coupling intravascular flow and interstitial flow in tumour tissue. The integrated model has been used to examine the influence of microvascular distribution, necrosis and vessel pruning on fluid flow, as well as the effect of heterogeneous vessel permeability. Our results reveal the level of nonuniformity in tumour interstitial fluid pressure (IFP), with large variations in IFP profile between necrotic and non-necrotic tumours. Changes in microscopic features of the vascular network can significantly influence fluid flow in the tumour where removal of vessel blind ends has been found to reduce IFP and promote interstitial fluid flow. Our results demonstrate the importance of incorporating microscopic properties of the tumour vasculature and intravascular flow when predicting fluid flow in tumour tissue.