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The Hemodynamics of Native and Surgical Aortic Valves with Regards to Wall Shear Stress and Residence Time


Rosakis, Alexandros Yiannis (2023) The Hemodynamics of Native and Surgical Aortic Valves with Regards to Wall Shear Stress and Residence Time. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/exsa-nm30.


Cardiovascular diseases are the leading causes of illness and death all around the world. The third most common cardiovascular disease is aortic stenosis (AS). AS is most commonly characterized as a stiffening of the native trileaflet aortic valve, which impedes blood flow into the aorta and puts extra stress on the heart. The aorta is the main artery that supplies oxygenated blood to the body. AS has been widely studied in the past. However, there has been little work in understanding the complex effects that non uniform stiffening of the aortic valve can have on the hemodynamics inside the aorta. The most effective treatment for AS is to replace the stiffened valve with a prosthetic valve. Care must be taken to ensure that the replacement actually performs better hemodynamically. A major metric for prosthetic valve performance is the transvalvular pressure drop which is a measure of how much pressure, and energy, is lost as the heart pumps blood through the valve. Generally speaking, larger valves exhibit a smaller pressure drop because they restrict the flow to a lesser degree. This phenomenon has led to a trend for surgeons to implant the largest prosthetic valve possible, and in some cases, to expanding the aorta to fit even larger valves. However, there has been relatively little work done on determining the effects of valve oversizing on the blood flow inside the Aorta. The aims of this study were two-fold. First, a model of AS was tested inside an in vitro aortic simulator in order to identify how different individual leaflet stiffnesses would affect blood flow. Digital particle image velocimetry (DPIV) was used to measure velocity profiles inside a model aorta. The DPIV results were used to estimate the wall shear stress and blood residence time. Our analysis suggests that leaflet asymmetry greatly affects the amount of WSS by vectoring the systolic jet and that stiffened leaflets have an increased residence time. This study indicates that valve leaflets with different stiffness conditions can have a more significant impact on wall shear stress than stenosis caused by the uniform increase in all three leaflets (and the subsequent increased systolic velocity) alone. Second, the experimental apparatus was used to test different prosthetic valve sizes and valve mounting methods in order to identify how they affected residence time inside the sinus bulge. Dye residence experiments and DPIV were used to measure fluid stasis in several different combinations of prosthetic valve sizes, sinus sizes, and valve mounting methods. Our results indicate that valve to sinus sizing and mounting method is very important and can lead to greatly increased residence time and thrombosis risk. We have also identified a metric that can predict the threshold at which valves become oversized.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Aortic Valve Hemodynamics
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Medical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Gharib, Morteza
Thesis Committee:
  • Ravichandran, Guruswami (chair)
  • Shapiro, Mikhail G.
  • Koochesfahani, Manoochehr
  • Gharib, Morteza
Defense Date:25 August 2022
Record Number:CaltechTHESIS:10032022-224522966
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for use in thesis
Rosakis, Alexandros Yiannis0000-0001-9170-1002
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15038
Deposited By: Alexandros Rosakis
Deposited On:25 Oct 2022 21:36
Last Modified:01 Nov 2022 19:17

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