-
Physiology Questions
Post any questions you have about physiology and hemodynamics
-
9 Replies
-
What parameter changes might best simulate pericardial constriction? And can respiration be added that alter intra-thoracic pressure?
-
Increases in systemic vascular resistance (SVR) would simulate peripheral vasoconstriction. SVR is listed in many of the input panels; in some, the total peripheral resistance (which constitutes SVR) is divided into two different resistances (small and large vessels) in which case the term Ra (sys) would be used to simulate vasoconstriction.
-
-
Appreciate the response. However i wanted to model PERIcardial constraint such as a constrictive,calcified pericardium. In a circuit-based model like Harvi, I am not certain how to do that. A hyperbolic decrease in pericardial compliance when total cardiac volume passes a set threshold seems needed. Happy to collaborate on implementation if that would be helpful.
Terry Bauch
-
Very sorry–I misread your initial question (I read peripheral rather than pericardial!).
Take a look at the chapter on pericardial disease in the student book. There’s an interactive associated with that chapter that has a slider to control pericardial stiffness (beta). At its default setting (0.01), it requires a lot of volume to induce full blown tamponade. But if you put a little volume in the pericardial space (eg 100 ml), you’ll see mild changes at that setting of pericardial stiffness. You can then make the pericardium stiffer and see more pronounced hemodynamics effects of that same volume.
Let me know if this is what you’re looking to do…. MLD
Addendum: Also, in the full simulator, look at the input menu item Ventricles & Peri. You can modulate both alpha and beta from this input panel.
-
This reply was modified 3 months ago by Marc.
-
This reply was modified 3 months ago by
-
And, yes, you can add changes in intrathoracic pressure and see systolic pressure variation magnified by the presence of pericardial fluid! In the anesthesia input panel, you can toggle between spontaneous and mechanical ventilation. You can also select different degrees of lung stiffness (this will change the peak pressure for a set tidal volume with mechanical ventilation). If you view a monitor plot, you can see the pressure variation with the ventilatory cycle on the PA and ABP tracings. BTW, another fun example of systolic pressure variation can be seen if you turn on V-pacing at a slightly different rate than the atrial rate (set by HR)–atrial and ventricular contraction come in an out of phase, generating a-waves on the CVP tracing when the RA contracts against a closed tricuspid valve, and reducing LV filling during that phase. Endless fun with the simulator!
-
-
I would love to try varying intrathoracic pressure, but I do not see an Anesthesia input panel on my version. Where can I find that one? I have 20 other ones that I looked over. Thanks!
-
I’m not sure why the anesthesia input was omitted from the professors menu list. I added that (and a few more!). Thanks for pointing that out!
-
Thank you! I can reproduce some helpful variations with respiration, and the AV dissociation trick with V pacing works perfectly.
I’m trying to simulate greater variations in intrathoracic pressure during respiration, to demonstrate clear changes on transvalvular mitral flow and AO pulse pressure, but even at Tidal Volume maxed to 1000cc, the pressure variation is relatively small. How might I increase the amplitude of the change? Is there an airway resistance parameter I can change? Thanks again. Terry
-
Glad you found the V pacing/AV dissociation. It’s a fun one as you can see cannon a-waves come and go, in addition to the SPV. I recently saw that during a difficult epicardial pacer placement in the OR to dx faulty sensing of the a-lead (despite the numbers on the interrogation suggesting it was working!–a great example of the importance of knowing how to interpret a cvp waveform!).
For the respiratory variation, you should be able to see mitral flow variability. Make sure you select mechanical ventilation. We haven’t modeled airflow dynamics, but you can change lung compliance to SEVERE (and increase TV to 1000) to maximize the intrathororacic pressure changes. Let me know if you have any trouble with that–should work.
-
Log in to reply.