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schiwei 12-01-2010 07:00 AM

Pulmonary Shunting, Please Explain?
 
How would blood flow obstruction during shunt cause pO2 and pCO2 to approach that of mixed venous blood? Should one consider contributions from healthy alveoli in this question or not? :scared:
Also, when V/Q approaches infinity how would pO2 and pCO2 approach that of inspired air?

varunshetty00 12-01-2010 08:39 AM

I'm not sure if you're asking the right question or whether I interpreted you correctly. Are u asking why is it considered a right to left shunt in case of an alveolar collapse?
If yes, then imagine AN alveoli with a capillary right nxt to it. air diffuses from the alveoli into capillary. If alvelolus is taken away, then the blood flows through the capillary without any oxygen-- thus it still has venous gas values as "functionally" it is still venous blood. This gives a situation "like" right to left shunt. as if blood from right side has entered left- which if u think about it has occurred in a way.

V/Q ratio is simple.
When v/Q reaches infinity, ventilation perfusion are the maximum they can be. Now the PO2 atmospheric air will not change no matter how hard we ventilate. thus with maximal ventilation and perfusion, the maximum po2 in blood (as even perfusion is proportionally increased with ventilation to match, it is the same as the air flowing "directly" from alveolus to blood) ; will be the same as atmospheric air.

I hope I have answered your question.
Guys, if I'm wrong anywhere please do let me know!

schiwei 12-01-2010 08:51 AM

Re:V/Q
 
The problem I have with V/Q approaching infinity is this : it implies that there is no perfusion. So given no perfusion, the amount of ventilation that goes on would be meaningless, blood would not be filled with oxygen, no matter what..so how does the pO2 increase then? :( how would a vacuum chamber necessarily still have air in it, in absolute measurable terms as evidenced by the pO2 in the blood?

americandoc 12-01-2010 08:54 AM

Quote:

Originally Posted by schiwei (Post 21231)
The problem I have with V/Q approaching infinity is this : it implies that there is no perfusion. So given no perfusion, the amount of ventilation that goes on would be meaningless, blood would not be filled with oxygen, no matter what..so how does the pO2 increase then? :(

v/q if equal to 1 only then the the ratio is perfectly matched ...


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