Computational Study of Abdominal Aortic Aneurysms with Severely Angulated Neck Based on Transient Hemodynamics Using an Idealized Model

Round 1

Reviewer 1 Report

The paper is devoted to computational study of abdominal aortic aneurysms with severely angulated neck. Computational predictions were performed considering idealized models for four severe proximal neck angulations of symmetric aneurysms. The simulation results showed the formation of regions with high and low wall shear stress, turbulent flow, and recirculation in the aneurysm sac depending on the angulation, which could have led to aortic wall weakness.

The paper is well-structured. The results are interesting. So, it can be published.

Author Response

Thank you for the reviewer’s time for reviewing the manuscript.

Reviewer 2 Report

The group of authors in the work entitled “Computational study of abdominal aortic aneurysms with se-verely angulated neck based on transient hemodynamics using an idealized model” analyzed flow patterns and their effect on wall shear stress  at abdominal aortic aneurysm walls through CFD simulations of incompressible, Newtonian, and transient blood flow in three-dimensional rigid models with different proximal neck angulations. The results of their CFD research showed that the angulations of the aortic neck describe the downstream blood flow, influencing flow turbulence and recirculation in the aneurysm. The authors concluded this can weaken the aortic wall and form high and low WSS regions. I find these results very interesting and I recommend this manuscript for publishing but after minor revision.

The authors conducted mesh independent analysis. They stated “Three different mesh densities were evaluated to confirm the mesh independence and validate the CFD solutions”. In my opinion authors did not in this way validate CFD solutions. Actually I did not see that authors compared results with more accurate results, for example experimental results and in this way validated CFD results. They wrote in the conclusion of the manuscript the following “We demonstrated through CFD simulations that the severity of proximal neck angulation, which cannot be reproduced in vivo, affects the hemodynamics.” Does it mean that authors cannot validate CFD results? How can we trust these results?

Please, put in line formulas (1) and (2).

The formula (2) has two numbers (2), please delete one.

Please, put in figure 2 units of physical magnitudes.

Please, put in figure 10 (c and d) units of physical magnitudes.

The way of representing of physical magnitudes and units in figures is non-uniform. Please, check the rules of the journal.

Author Response

I am appreciated in your dedication and time to review the manuscript and give the constructive comments to improve the content of manuscript. I would like to respond and clarify as the following.

The answer is in BLUE. The revised or edited part is highlighted with yellow color.

Reviewer suggestions:

The group of authors in the work entitled “Computational study of abdominal aortic aneurysms with se-verely angulated neck based on transient hemodynamics using an idealized model” analyzed flow patterns and their effect on wall shear stress at abdominal aortic aneurysm walls through CFD simulations of incompressible, Newtonian, and transient blood flow in three-dimensional rigid models with different proximal neck angulations. The results of their CFD research showed that the angulations of the aortic neck describe the downstream blood flow, influencing flow turbulence and recirculation in the aneurysm. The authors concluded this can weaken the aortic wall and form high and low WSS regions. I find these results very interesting and I recommend this manuscript for publishing but after minor revision.

1. The authors conducted mesh independent analysis. They stated “Three different mesh densities were evaluated to confirm the mesh independence and validate the CFD solutions”. In my opinion authors did not in this way validate CFD solutions. Actually, I did not see that authors compared results with more accurate results, for example experimental results and in this way validated CFD results. They wrote in the conclusion of the manuscript the following “We demonstrated through CFD simulations that the severity of proximal neck angulation, which cannot be reproduced in vivo, affects the hemodynamics.” Does it mean that authors cannot validate CFD results? How can we trust these results?

Answer:

Thank you for your comment and concern about our statements in the Materials and Methods section and the Conclusion section. We would like to respond as following

This study performed only computational simulation using CFD and firstly we looked at the proper mesh quality that suitable for the computational simulation by mesh independence check. We did not validate the CFD results as the reviewer mentioned. Therefore, we have deleted “and validate the CFD solutions” to make it clear and no confusion in validation meaning (as shown below). Because our work was performed in a severe degree of angulated neck condition; there were few studies to be compared. However, we tried to find with existing studies to discuss and support our simulation finding such as work done by Xenos et al., and Drewe et al. As the reviewer raised this concern, in the future work, we will do the mock up experimental study and compare the CFD results with the experimental mock up.

The grid convergence index reflects the computational error resulting from Richardson extrapolation. Three different mesh densities were evaluated to confirm the mesh independence. The refinement of mesh elements is illustrated in Figure 2; the tetrahedral four-node elements are finer near the aortic wall [31].

As we mentioned in the Conclusion section “We demonstrated through CFD simulations that the severity of proximal neck angulation, which cannot be reproduced in vivo, affects the hemodynamics.”, we meant, in the reality (in the body), it cannot manipulate the different degree (60^o-90^o) of angulated neck of aneurysm to get the geometry from the human subject or animal subject to perform the computational simulation. However, as we respond above, we tried to find with existing studies to discuss and support our simulation finding such as work done by Xenos et al., and Drewe et al. Anyway, as the concern raised by the reviewer, we have decided to delete “which cannot be reproduced in vivo” to make it clear and not vague.

We demonstrated through CFD simulations that the severity of proximal neck angulation affects the hemodynamics.

2. Please, put in line formulas (1) and (2).

The formula (2) has two numbers (2), please delete one.

Answer:

Thank you for your comments. We have done.

3. Please, put in figure 2 units of physical magnitudes.

Answer:

Thank you for your comments. Figure 2 is a mesh generation which has no unit of physical magnitudes. However, we have rechecked this comment and we have found that Figure 4 and Table 1 need to have a unit of physical magnitude as “m/s” because is velocity. Therefore, we have added it.

4. Please, put in figure 10 (c and d) units of physical magnitudes.

Answer:

Sorry to make the reviewer a mistake of referred figure. We put two of Figure 10, so it should be Figure 11. As Figure 11 c and d show OSI values, this parameter has no unit because it is calculated from the ratio of wall shear stress. ( Please see the equation in the attached file).

5. The way of representing of physical magnitudes and units in figures is non-uniform. Please, check the rules of the journal.

Answer:

Thank you for this comment. We would like to explain that our study performed two aspects of results. First one is a relative value or a ratio that compared with maximum value of each parameter such as velocity ratio (VR), pressure ratio (PR). Second aspect is an absolute value such as velocity, wall shear stress. Therefore, we confirm that we present proper physical magnitudes and units in figures.

Author Response File: Author Response.pdf