coronary project steady simulation

[Luca Gontier]

Hi, i downloaded coronary project folder from the website. I wanted to try the steady simulation as in the folder, I know there is the guide for a pulsatile flow on the site but i wanted the steady. I can not understand how the resistances of the coronary cap have been calculated. there is a guide or you can you help me.

Thanks

[Justin Tran]

Hi Luca,

Thank you for your interest in SimVascular and the coronary project in particular! To run a steady simulation, you will need to modify the step "Inflow boundary condition" in the tutorial. When you pull up the window called "Set Inlet/Outlet BCs" on the "cap_aorta" surface, you will see there is a button called "Flow rate (from file)". Here, the tutorial will ask you to input the file "scaled_pulse_flow.flow", which is a pulsatile flow waveform as you described. To make this steady, you will need to specify a steady flow file. An example of such a file is given below:

0 -80
0.3 -80

Copy this into a text file called "const_inlet.flow", save it, then load it into SimVascular using the steps above.

The coronary resistances are computed based on a few factors. The first factor is that we assume a cardiac output and mean arterial pressure for this patient (in practice, this information is readily available for any patient-specific model). We compute a "total resistance" by dividing the mean arterial pressure by the cardiac output, similar to Ohm's Law:

R_tot = P/Q

From here, we assume that 4% of the cardiac output goes to the coronaries, and 96% of the cardiac output goes to the systemic circulation through the aorta. This assumption is widely supported in the literature. This means that the total coronary resistance will be 24x the total systemic resistance. From here, we assume that all the coronary outlet resistances are connected in "parallel" fashion, and that the relative resistance values are inversely proportional to the outlet size. In other words, we want to "split" the total coronary resistance among the different outlets using the outlet area as a scaling factor. One way to express this mathematically is given by the equation in the section "Selection of parameter values".

After this step, we will have a scaled resistance for each coronary outlet in our model. We split this in "series" among the 3 coronary resistances (Ra,i, Ra,micro, and Rv) using empirical relations shows in the section "Selection of parameter values". SimVascular will perform all these calculations for you, so you just need to follow the steps in the documentation.

Hope that helps! Let us know if anything was unclear or if you need further assistance. Thank you again for your interest and use of SimVascular!

[Luca Gontier]

thanks for your very detailed answer,
I still have a few question.
The R_tot in the formula is the resistance for the aortic outflow?
and the total coronary resistance will be 24x the total systemic resistance, this systemic resistance is the previous R_tot?
When calculating the total resistance of the coronary arteries, assuming I have only considered 4% of cardiac output, you divide it into 70-30 for left and right artery and then calculate the resistance for each outlet separate for left and right outlet, or consider total coronary resistance and divide that in all the outlets? Similar to the process to calculate the capacitance who separate left and right branches.
I calculate the single resistance for each outlet and insert the resistance in BC type ("resitance") it is correct (because i cannot use coronary outlet because i need otherwise to insert a flow file pulsatile), and after this i need to split the resistance, but i cannot insert the Ra:Ra-micro:Rv) ratio


Thanks