Derivation of a simplified relation for assessing aortic root pressure drop incorporating wall compliance

Porcine and bovine aortic valve comparison for surgical optimization: A fluid-structure interaction modeling study

BACKGROUND

Porcine aortic valve (PAV) and bovine aortic valve (BAV) are commonly used in aortic valve replacement (AVR) surgeries. A detailed comparison for their hemodynamic and structural stress/strain performances would help to better understand valve cardiac function and select valve type and size for AVR outcome optimizations.

METHODS

Eight fluid-structure interaction models were constructed to compare hemodynamic and stress/strain behaviors of PAV and BAV with 4 sizes (19, 21, 23, and 25 mm). Blood flow velocity, systolic cross-valve pressure gradient (SCVPG), geometric orifice area (GOA), flow shear stresses (FSS), and stress/strain were obtained for comparison.

RESULTS

Compared with PAV, BAV has better hemodynamic performance, with lower maximum flow velocity (7.17%) and pressure (9.82%), smaller pressure gradient (mean and peak SCVPG: 8.92% and 9.28%), larger GOA (9.56%) and lower FSS (6.61%). The averages of the mean and peak net pressure gradient values from 4 BAV models were 8.10% and 8.35% lower than that from PAV models. Larger valve sizes for both PAV and BAV had improved hemodynamic performance. Maximum flow velocity, pressure, mean SCVPG and maximum FSS from 25 mm BAV were 36.80%, 15.81%, 39.05% and 38.83% lower than those from 19 mm BAV. The GOA of PAV and BAV 25 mm Valve were 43.75% and 33.07% larger than 19 mm valves, respectively. BAV has lower stress on the leaflets than PAV.

CONCLUSIONS

BAV had better hemodynamic performance and lower leaflets stress than PAV. More patient studies are needed to validate our findings.

Fluid structure interaction modelling of aortic valve stenosis: Effects of valve calcification on coronary artery flow and aortic root hemodynamics

BACKGROUND AND OBJECTIVE

Coronary artery diseases and aortic valve stenosis are two of the main causes of mortality and morbidity worldwide. Stenosis of the aortic valve develops due to calcium deposition on the aortic valve leaflets during the cardiac cycle. Clinical investigations have demonstrated that aortic valve stenosis not only affects hemodynamic parameters inside the aortic root but also has a significant influence on the coronary artery hemodynamics and leads to the initiation of coronary artery disease. The aim of this study is to investigate the effect of calcification of the aortic valve on the variation of hemodynamic parameters in the aortic root and coronary arteries in order to find potential locations for initiation of the coronary stenoses.

METHODS

Fluid structure interaction modelling methodology was used to simulate aortic valve hemodynamics in the presence of coronary artery flow. A 2-D model of the aortic valve leaflets was developed in ANSYS Fluent based on the available echocardiography images in literature. The k-ω SST turbulence model was utilised to model the turbulent flow downstream of the leaflets.

RESULTS

The effects of calcification of the aortic valve on aortic root hemodynamics including transvalvular pressure gradient, valve orifice dimeter, vorticity magnitude in the sinuses and wall shear stress on the ventricularis and fibrosa layers of the leaflets were studied. Results revealed that the transvalvular pressure gradient increases from 792 Pa (∼ 6 mmHg) for a healthy aortic valve to 2885 Pa (∼ 22 mmHg) for a severely calcified one. Furthermore, the influence of the calcification of the aortic valve leaflets on the velocity profile and the wall shear stress in the coronary arteries was investigated and used for identification of potential locations of initiation of the coronary stenoses. Obtained results show that the maximum velocity inside the coronary arteries at early diastole decreases from 1 m/s for the healthy valve to 0.45 m/s for the severely calcified case.

CONCLUSIONS

Calcification significantly decreases the wall shear stress of the coronary arteries. This reduction in the wall shear stress can be a main reason for initiation of the coronary atherosclerosis process and eventually results in coronary stenoses.

Fiber-reinforced computational model of the aortic root incorporating thoracic aorta and coronary structures

Cardiovascular diseases are still the leading causes of death in the developed world. The decline in the mortality associated with circulatory system diseases is accredited to development of new diagnostic and prognostic tools. It is well known that there is an inter relationship between the aortic valve impairment and pathologies of the aorta and coronary vessels. However, due to the limitations of the current tools, the possible link is not fully elucidated. Following our previous model of the aortic root including the coronaries, in this study, we have further developed the global aspect of the model by incorporating the anatomical structure of the thoracic aorta. This model is different from all the previous studies in the sense that inclusion of the coronary structures and thoracic aorta into the natural aortic valve introduces the notion of globality into the model enabling us to explore the possible link between the regional pathologies. The developed model was first validated using the available data in the literature under physiological conditions. Then, to provide a support for the possible association between the localized cardiovascular pathologies and global variations in hemodynamic conditions, we simulated the model for two pathological conditions including moderate and severe aortic valve stenoses. The findings revealed that malformations of the aortic valve are associated with development of low wall shear stress regions and helical blood flow in thoracic aorta that are considered major contributors to aortic pathologies.

3D physiological model of the aortic valve incorporating small coronary arteries

The diseases of the coronary arteries and the aortic root are still the leading causes of mortality and morbidity worldwide. In this study, a 3D global fluid-structure interaction of the aortic root with inclusion of anatomically inspired small coronary arteries using the finite element method is presented. This innovative model allows to study the impact and interaction of root biomechanics on coronary hemodynamics and brings a new understanding to small coronary vessels hemodynamics. For the first time, the velocity profiles and shear stresses are reported in distal coronary arteries as a result of the aortic flow conditions in a global fluid-structure interaction model.

The impact of the aortic valve impairment on the distant coronary arteries hemodynamics: a fluid-structure interaction study

Atherosclerosis is still the leading cause of death in the developed world. Although its initiation and progression is a complex multifactorial process, it is well known that blood flow-induced wall shear stress (WSS) is an important factor involved in early atherosclerotic plaque initiation. In recent clinical studies, it was established that the regional pathologies of the aortic valve can be involved in the formation of atherosclerotic plaques. However, the impact of hemodynamic effects is not yet fully elucidated for disease initiation and progression. In this study, our developed 3D global fluid-structure interaction model of the aortic root incorporating coronary arteries is used to investigate the possible interaction between coronary arteries and aortic valve pathologies. The coronary hemodynamics was examined and quantified for different degrees of aortic stenosis varying from nonexistent to severe. For the simulated healthy model, the calculated WSS varied between 0.41 and 1.34 Pa which is in the atheroprotective range. However, for moderate and severe aortic stenoses, wide regions of the coronary structures, especially the proximal sections around the first bifurcation, were exposed to lower values of WSS and therefore they were prone to atherosclerosis even in the case of healthy coronary arteries.