Lec 26 Congenital Heart DIsease Flow Dynamics Flashcards Preview

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Flashcards in Lec 26 Congenital Heart DIsease Flow Dynamics Deck (15)
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What determines the driving force for systemic flow? what about the pulmonary circulation?

systemic = pressure difference between aorta and central venous pressure pushing blood through the heart

pulmonary = pressure difference between pulm artery and LA


What is Ohm's law for flow?

delta P = Q * R

pressure drop = mean flow * mean resistance


Why do we measure average rather than instantaneous flow?

- easier to conceptualize and measure
limitation: instantaneous behavior of circulation can be obfuscated by these models


What is the equation for systemic resistance?

Rs = (Pao - Pra) / CI

[R = delta P/flow]

Rs = systemic resistance
Pao = aortic P
Pra = right atrium P
CI = cardiac index


What is cardiac index?

CI = cardiac output indexed to body surface area


What happens to PVR after birth?

starts out really high and declines to adult level
means there is a rapid decline in pulm/systemic resistance ratio


What is normal mature level of PVR [pulm ascular resistance]?

2 woods units


What 3 factors alter resistance to blood flow?

1. blood viscosity
2.. vessel length
3. vessel radius [most important]


What determines blood viscosity?

- high hematocrit [Hct] and protein conc --> high viscosity --> increase resistance


What is poiseulle's equation?

R = 8 * Ln/pi*r^4


What is relationship relative flow through parallel outlets from single reservoir?

relative flow rate proportional to relative resistances


What happens to resistance when resistors are added in parallel?

resistance lowered!


What do we assume if non-restrictive "large" VSD when we are calculations flows/pressures?

- systolic RV and LV pressures equalize thus aortic and pulmonary artery pressure equal in systole


How do you determine Qp/Qs the pulmonary to systemic flow ratio?

Qp/Qs is inversely proportional to resistance ratio Rp/Rs

--> the ratio of resistances determines the amount of shunting through VSD


How to model smaller/restrictive VSD?

from point of view of LV: "pulmonary resistance" part of the equation = combo of VSD resistance and pulm vascular resistance in series

--> increased resistance of small VSD affects Qp/Qs ratio by lowering pulm artery:aortic P ratio