The ascending aorta houses the sinus bulge (also called the aortic sinus or sinus of Valsalva), a dilation of the aorta around the aortic valve. Aortic stenosis is characterized by a decrease in the effective opening area of the aortic heart valve with three leaflets. However, existing studies typically model AS as a symmetrical decrease in the effective opening area of the aortic valve.
A water column connected to the end of the glass tube provided physiological back pressure of 100 mmHg on the valve during diastole. We apply this to the flow in the aorta as a measure of the vorticity injected during each systole. The GOA of a valve refers to the area of the opening that a valve creates when it.
The fluid streams were seeded with silver-coated ceramic microparticles (20 μm in diameter) upstream of the valve. Care was taken to ensure that the laser plate was in the same location during all tests. The inner and outer edges of the glass aorta and valve were masked to be removed from quantification.
The walls of the glass container were identified by hand and the velocity on the wall was clamped to zero.
Results
To quantitatively measure the effects of vane asymmetry, the 20 mm fluid velocity profile downstream of the valve was analyzed. The fluid velocity profile during peak systole for each experimental setup is shown in Figure 3.2. As expected, the ST valve configuration produces a fairly uniform velocity profile with a peak velocity of 0.85 m/s.
Wall shear stress is directly related to the velocity gradient of the fluid flow near the wall. However, Figure 3.3 shows how valve stiffness (resulting in angled beam path) plays a much larger role in the distribution of wall shear stress. Furthermore, the A2 configuration reduces the average wall shear stress on the inner wall of the arch, which may be caused by a decrease in the amount of reverse flow near the inner wall.
It is immediately clear that the 25mm Tria valve removes less dye after each successive cycle. Overall, each configuration removed most of the dye in a single cardiac cycle with very little variation. The formation number can be understood as a measure of the vorticity injected into the aorta and is influenced by the GOA of the valve and the cardiac output of the heart.
Instead, the dominant parameter in this area is the physical distance of the gap between the post and sinus wall as seen in figure 3.12. Dye experiments provided a measure of the impact of Cor-Knots on the blood flow around the valves. The injected dye remains attached to the outer sinus wall for more than two cardiac cycles when Kor nodes are present, whereas the normally mounted valve removes most of the dye from the wall after a single cycle.
However, when the valve size decreases to 21 mm, the dye is efficiently removed regardless of the presence of Cor-Knots and cardiac output (Figure 3.16). PIV provided time-varying velocity information around the different valves that was used to measure the effective mixing and fluid stasis around the cork knots at the bottom of the valve. In all cases, the valves equipped with Cor-Knots underperform and fall under the trend of valves without Cor-Knots.
Finally, figure 3.19 shows the mean velocity fields of the 23 mm Tria valve with and without the crust joint. The presence of separate cortical nodes attenuates the mean velocity in their vicinity at low cardiac outputs.
Discussion
The stiffening of the blades also had a major influence on the residence time of the fluid immediately adjacent to the valves. The data presented above can be used to validate detailed numerical simulations of the above-mentioned disease. Second, it shows how WSS can be controlled by careful manipulation of individual aortic valve leaflet thicknesses.
Increasing formation number leads to linearly increasing mixing measures (mean and standard deviation of velocity) in the regions near the valve blades. Due to the geometry of the trileaflet valves, these areas were the most "open" and allowed the flow in the ascending aorta to more easily interact with the fluid near the leaflets. Therefore, the constant increase of the two mixing criteria with increasing formation number can be expected because as the formation number grows, more vorticity is added to the fluid in the aorta and the velocity of the systolic jet also increases.
However, the formation number does not have such a strong effect on the fluid located between the poles of the valve and the sinus wall (figure 3.11). The second way valve size affects aortic hemodynamics is that larger valves will inherently take up more volume within the sinus bulge and the gap between their posts and the side of the sinus wall will be smaller. Referring to figure 3.12, we see that the gap distance for this valve was 1.57 mm and that both the mixing criteria were 0.01 m/s.
This is most likely due to the smaller gross effective area of the valve and thus the higher formation number. To account for formation number and gap distance, Figure 4.1 presents plug-to-sinus wall mixing criteria as a function of the product of formation number and the ratio of gap distance to valve diameter. As previously stated, human sinusoidal dimensions vary from 27mm to 36mm, and the 25mm Trio valve is an oversized configuration for a 32mm sinusoid.
In the normal installation configuration, all valve configurations tested were able to remove paint after one cycle. This reduction in mixing criteria was even present in the more open area of the valve near the flaps. The gap distance is influenced by the external size of the implanted valve and the size of the sinus cusps.
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Appendix A
