Hey yall:

Can anyone help me get this alveolar air equation?

I know it's PAO2 = PIO2 - (PAO2/R) + F.

The situation is this: breathing at room air, at sea level. PaO2 is 100, PaCO2 is 40. Double the alveolar ventilation for 10 minutes, what is the effect on PO2 & PCO2, with R=0.8

Answer is: PO2 = 125, PCO2 = 20.

Rationale I got was: as alveolar ventilation increases, the alveolar Po2 will also increase. Doubling alveolar ventilation, however, cannot double PAo2 in a person whose alveolar Po2 is already 104 mm Hg because the highest PAo2 one could possibly achieve (breathing air at sea level)

My thoughts: I get that the CO2 will decrease by 1/2 when you double the ventilation. But I thought your O2 can go up to 150. I can't figure out how to plug in the #s into this equation. Am I looking at it all wrong?????

Thanks in advance for any help... My brain is fried!!!!! :aargh4:

- Becky