Difference between R-L shunt and V/Q mismatch ?

[zeevee]

If there is no ventilation there is some kind of obstruction so V/Q = 0 ( oxygen saturation wont help if complete)
If there is no perfusion usually its an embolism v/Q = ∅ ( infinity) ( oxygen saturation can help)

In either case its a V/Q mismatch

what is a rt -left shunt , how is that different from V/Q mismatch ?

@ forum greats please help and if you could help me with the progesterone challenge test that would be awesome

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[zhopv10]

They are on the same spectrum, v/q mismatch is not quite as little oxygen as a full shunt, full shunt is the blood receives no oxygen by either mechanism you mentioned. Giving oxygen would not help to any appreciable degree in a shunt. That was my understanding anyway


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[zeevee]

Thanks zhopv .I agree with you .A shunt is a complete obstruction. I found a Q in BRS regarding this

A person with a ventilation/perfusion (V/Q) defect has hypoxemia and is treated with supplemental O2. The supplemental O2 will be most helpful if the person’s predomi- nant V/Q defect is

(A)dead space
(B)shunt
(C)high V/Q
(D)low V/Q

(E)V/Q=0
(F)V/Q=×

Answer is D

Reasoning is as follows :
SupplementalO2(breathinginspiredairwithahighPO2)ismost helpful in treating hypoxemia associated with a ventilation/perfusion (V/Q) defect if the predominant defect is low V/Q. Regions of low V/Q have the highest blood flow. Thus, breathing high PO2 air will raise the PO2 of a large volume of blood and have the greatest influence on the total blood flow leaving the lungs (which becomes systemic arterial blood). Dead space (i.e., V/Q = ∞ has no blood flow, so supplemental O2 has no effect on these regions. Shunt (i.e., V/Q = 0) has no ventilation, so supplemental O2 has no effect. Regions of high V/Q have little blood flow, thus raising the PO2 of a small volume of blood will have little overall effect on systemic arterial blood.

 

[aioo]

If there is no ventilation there is some kind of obstruction so V/Q = 0 ( oxygen saturation wont help if complete)
If there is no perfusion usually its an embolism v/Q = ∅ ( infinity) ( oxygen saturation can help)

In either case its a V/Q mismatch

what is a rt -left shunt , how is that different from V/Q mismatch ?

@ forum greats please help and if you could help me with the progesterone challenge test that would be awesome

I think R-L shunt is a cardiac shunt. So deoxygenated blood is mixing with oxygenated and therefore also causes hypoxemia and this, like the pulmonary shunt(v/q-->0) is not significantely fixable with extra O2. The difference is that there is no v/q mismatch in the cardiac shunt and the A-a ratio is also not elevated(in pulm shunt is is).

 

[zhopv10]

Oh good catch I didn't even notice the question about right to left shunt. That's def cardio as aioo said


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[zeevee]

awesome .yes thats exactly it.Case closed thanks to you

I think R-L shunt is a cardiac shunt. So deoxygenated blood is mixing with oxygenated and therefore also causes hypoxemia and this, like the pulmonary shunt(v/q-->0) is not significantely fixable with extra O2. The difference is that there is no v/q mismatch in the cardiac shunt and the A-a ratio is also not elevated(in pulm shunt is is).