Mistake in BRS Phys???

[Mossjoh]

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Maybe I'm not understanding the definition of mixed venous P02...but this answer seems wrong to me..

"If an area of the lung is not ventilated because of bronchial obstruction, the pulmonary capillary blood serving that area will have a PO2 that is....

A. equal to atmospheric PO2
B. equal to mixed venous PO2
C. equal to normal systemic arterial PO2
D. higher than inspired PO2
E. lower than mixed venous PO2"

BRS Physiology says the answer is B. equal to mixed venous PO2

I disagree. I thought mixed venous PO2 was once the blood combines with the rest of the venous blood in the pulmonary vein that IS oxygenated! This lowers the overall PO2 of pulmonary venous blood. Yet....my brain says the blood in the capillary (which the question asks for) would be lower than the mixed venous PO2 and equal to systemic venous PO2 (about 40mmHg)

Right???


Mossjoh

 

[mpp]

Mixed venous blood is blood in the right atrium, mixed from all the veins in the body...not the pulmonary vein.

 

[Idiopathic]

Thats correct, this blood is shunted and will have the same MVO2 as that blood returning from the systemic circulation (which is the definition of MVO2)