Pressure waveforms at different outlets look identical

[Linnea Warburton]

Hello,

I am attempting to use SimVascular to determine the pressure waveforms at the outlets of an aorta with an aortic coarctation. I am using the 2019 version of SimVascular, the svSolver, and RCR boundary conditions. Unfortunately, when I run the simulations my results show that the pressure waveforms at the supra-aortic outlets and the descending aorta are exactly the same. In reality, there should be an almost 20 mm Hg difference between the peak pressure at these different outlets. The pressure waveforms at the outlets before the coarctation and after the coarctation should be drastically different, but my results from the all-results_pressures file show no difference.

I am using flow data at the ascending and descending aorta, and the RCR Windkessel boundary conditions at the LSA, LCC, and Braciocephalic outlets with the following values
LSA Outlet: 452, 0.0002175, 8586
LCC Outlet: 474.8, 0.0001857, 9627
Brachiocephalic: 330.2, 0.0002967, 6275

Are there different settings that I should be using so that there is more variation between my pressure waveforms? I have attached images of the pressure waveforms.

Thank you for your time.

[Weiguang Yang]

What are the RCR values for the descending aorta?
First I think you can verify if RCR is prescribed correctly on the outlets. For each outlet, use the outlet flow data and RCR values to calculate the analytical outlet pressure. The 3D outlet pressure should be the same as this analytical expression. See Eqn 6 in https://arxiv.org/pdf/1012.0736.pdf

Second, maybe you can test a zero pressure condition for all outlets. Will you have a pressure drop of 20 mmHg?

Third, C seems little big. The pressure pulse is ~4000 (if this is in cgs units, it is about 3 mmHg). Try to reduce C by a magnitude.

[Linnea Warburton]

Hello!

Thank you for your reply, I appreciate it very much. I used the equation that you pointed out and from my calculations, the RCR values are not being prescribed correctly on the outlets, as the output of the simulations is very different than the results of the equation. Even when I drastically vary the RCR values between the outlets, the simulation shows the same pressure waveforms from all of the different outlets.

I altered the C values by a magnitude as you suggested

I am using the "Convert Results" button and the all_results_pressures file as well as viewing my results in Paraview, but is there a better way to look at the pressures at the outlets?

I am not sure why the pressure waveforms all look identical. The RCR values for the descending aorta are 139.9 0.001235 1857

Thank you for your help! It is greatly greatly appreciated.

[Weiguang Yang]

If the outlet pressure and flow do not agree with the analytical solution, it seems the boundary condition is not correctly imposed. You may check the presolver script (.svpre) and the solver.inp to see if the outlet ids are tagged and listed correctly in the solver.inp. If IDs 1, 2 and 3 are assigned to outlets 1, 2 and 3 in the presolver script, IDs 1,2 and 3 should be listed in the solver.inp and rcrt.dat should contain the RCR values for outlets 1, 2 and 3 in the same order. If you already verify these, the pressure and flow still do not make sense. I would do the following to debug. 1. Test a single outlet with RCR. Is RCR pressure/flow correct? 2. Test the same CoA model with zero pressure. Is there any pressure drop across the coarctation? 3. Use resistance boundary condition for the CoA model. By varying resistance values, is outlet flow rate changed? Does outlet pressure-flow relationship make sense?

Yes, the txt files list pressure/flow for outlets and inlets generated by the postsolver are the files you should use.