Experimental Insight into the Hemodynamics and Perfusion of Radiological Contrast in Patent and Non-patent Aortic Dissection Models
In a curved vessel such as the aortic arch, the velocity profile closer to the aortic root is normally skewed towards the inner curvature wall, while further downstream along the curve, the velocity profile becomes skewed towards the outer wall. In an aortic dissection (AD) disease, blood velocities in the true lumen (TL) and false lumen (FL) are hypothesized to depend on the proximity of the entry tear to the root of aortic arch. Faster velocity in the FL can lead to higher hemodynamic loading, and pose tearing risk. Furthermore, the luminal velocities control the perfusion rate of radiological contrast media during diagnostic imaging. The objective in this study is to investigate the effect of AD disease morphology and configuration on the blood velocity field in the TL and FL, and on the relative perfusion of radiological enhancement agents through the dissection.
Eight in vitro models were studied, including patent and non-patent FL configurations. Particle image velocimetry (PIV) was used to quantify the AD velocity field, while laser-induced fluorescence (LIF) was implemented to visualize dynamical flow phenomena and to quantify the perfusion of injected dye, in mimicry of contrast-enhanced computed tomography (CT).
The location of the proximal entry tear along the aortic arch in a patent FL had a dramatic impact on whether the blood velocity was higher in the TL or FL. The luminal velocities were dependent on the entry/reentry tear size combination, with the smaller tear (whether distal or proximal) setting the upper limit on the maximal flow velocity in the FL. Upon merging near the distal reentry tear, the TL/FL velocity differential gave rise to the roll up and shedding of shear layer vortices that convected downstream in close proximity to the wall of the non-dissected aorta. In a non-patent FL, the flow velocity was practically null with all the blood passing through the TL. LIF imaging showed much slower perfusion of contrast dye in the FL compared to the TL. In a patent FL, however, dye had a comparable perfusion rate appearing around the same time as in the TL.
Blood velocities in the TL and FL were highly sensitive to the exact dissection configuration. Geometric case A1R, which had its proximal entry tear located further downstream along the aortic arch, and had its entry and reentry tears sufficiently sized, exhibited the highest FL flow velocity among the tested models, and it was also higher than in the TL, which suggest that this configuration had elevated hemodynamic loading and risk for tearing. In contrast-enhanced diagnostic imaging, a time-delayed acquisition protocol is recommended to improve the detection of suspected cases with a non-patent FL.
KeywordsPatent false lumen Stanford type A PIV LIF Shear layer vortex Contrast computed X-ray tomography (CT) Magnetic resonance (MR) Tear propagation
Mr. J. Zullikian and Mr. J. Nassif performed the CNC machining of the models. Initial development of this study took place in the experimental fluid dynamics MECH-609 course given in 2016 at AUB. GFO thanks his sabbatical host Prof. S.L. Ceccio at the U. Michigan where the writing of this manuscript was completed. Feedback from the anonymous reviewers is highly appreciated.
Support was provided by an internal grant from the AUB University Research Board.
Conflict of interest
Elie Salameh declares that he has no conflict of interest. Charbel Saade has received research funding from GE healthcare USA. Ghanem Oweis declares that he has no conflict of interest.
No human studies were carried out by the authors for this article. No animal studies were carried out by the authors for this article. No cell culture studies were carried out by the authors for this article.
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