Pulmonary Vascular Resistance

[seminoma]

I always seem to struggle with vascular resistance relationships. UW says squatting can decrease pulmonary vascular resistance based on the increase in pulmonary blood volume.

I understand that squatting = increased afterload = reduced flow from pulmonary vein to LA = increased pulmonary blood volume. But how does the increase in pulmonary blood volume decrease vascular resistance?

Edit: Is it because delta P is relatively decreased and therefore causes a compensatory decrease in resistance in order to maintain constant Q?

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[aspiringmd1015]

i dont think its the blood volume thats decreasing resistance, its the increasd afterload that will work upstream to decrease the vascular resistance. Not sure though, could be totally wrong

 

[carnelian]

I interpreted it as squatting increases systemic vascular resistance -> relative decrease in pulmonary resistance (compared to the increase in systemic resistance) -> more blood will be directed to the lungs (blood prefers route of least resistance). Ie. the effect is mostly on systemic circulation, not pulmonary

 

[solitarius]

But how does the increase in pulmonary blood volume decrease vascular resistance?

It doesn't.

Squatting -> Increase blood volume -> increased forward pressure to overcome pulmonary resistance. Dynamics are similar to a shunt.

 

[seminoma]

It doesn't.

Squatting -> Increase blood volume -> increased forward pressure to overcome pulmonary resistance. Dynamics are similar to a shunt.

So UW is wrong? OP is almost verbatim from UW.

 

[pd1112]

The effect with squatting is primarily increased venous return, because you decrease gravity and create flow towards the heart from the area of the compressed veins, which would compresses before the thicker-walled arteries. This would increase flow into the pulmonary circuit and pressure will increase, which results in compensatory decrease in resistance to normalize the pressure.

 

[Transposony]

Doesn't Rapid squatting ---> increases Preload & Sustained squatting ---> increases Afterload ?

 

[pd1112]

Doesn't Rapid squatting ---> increases Preload & Sustained squatting ---> increases Afterload ?

I think that's correct.

 

[sloop]

Are we referring to squatting in Eisenmenger Syndrome or what? What is the context of the question?

 

[Transposony]

But how does the increase in pulmonary blood volume decrease vascular resistance?

Pulmonary circuit is a passive, highly compliant, high-flow, low-pressure & low-resistance system.
Therefore,
Increased increased blood volume --> increased pulmonary arterial pressure --> pulmonary veins stretch + recruitment of pulmonary capillaries --> decreased resistance.

 

[seminoma]

Are we referring to squatting in Eisenmenger Syndrome or what? What is the context of the question?

Squatting in a normal person. The question was about how squatting helps in Tetralogy of Fallot, but part of the explanation was explaining squatting in a normal person (the part that I don't get).

 

[seminoma]

Pulmonary circuit is a passive, highly compliant, high-flow, low-pressure & low-resistance system.
Therefore,
Increased increased blood volume --> increased pulmonary arterial pressure --> pulmonary veins stretch + recruitment of pulmonary capillaries --> decreased resistance.

Nice. I always forget about capillary recruitment. Good call man; when's your exam?

 

[Transposony]

Nice. I always forget about capillary recruitment. Good call man; when's your exam?

Yeah, Same story. When I read about it, it all makes sense but when faced with a question it takes time to recall or can't recall at all.
Guess I need more practice and that's why haven't decided about the exam yet.