Question about V/Q mismatch

[imraan47]

I have a question for pulmonary system if anyone can help.
in the case of V/Q mismatch i understand that PO2 will decrease and so the ventilation will increase. But i dont understand why the PCO2 will decrease?
Because if you are hypoventilating, the PO2 will decrease and so PCO2 will actually increase as that air wont even reach the alvelolar side. So mainly it will stay in the dead space. Pass program says its this scenrio the PCO2 will decrease and its throwing me Thanks

[RussianJoo]

Originally Posted by imraan47

I have a question for pulmonary system if anyone can help.
in the case of V/Q mismatch i understand that PO2 will decrease and so the ventilation will increase. But i dont understand why the PCO2 will decrease?
Because if you are hypoventilating, the PO2 will decrease and so PCO2 will actually increase as that air wont even reach the alvelolar side. So mainly it will stay in the dead space. Pass program says its this scenrio the PCO2 will decrease and its throwing me Thanks

umm pass program is wrong... if you're hypoventilating pco2 will increase. but that's not even what the v/q miss match is all about.. it's about the fact that you get more ventilation in the upper lobes than perfusion due to gravity, and thus v/q approaches infinity, and at the base of the lungs you have an increase in both ventilation and perfusion due to gravity but there's a bigger increase in perfusion than ventilation and thus the v/q approaches zero or at least approaching zero.