View Full Version : Alveolar PO2 during inspiration and expiration

03-22-2006, 02:54 PM
Alveolar PO2 does not change by more than 3 mmHg during expiration, but how is this PO2 maintained, especially if expiratory airflow is laminar at rest (could maybe see how if it was turbulent)? No additional oxygen is being introduced (or so it would seem by the direction of airflow) and blood is continually and quickly taking up oxygen.

03-22-2006, 06:25 PM
I don't know if this answer your question -- but take consideration of the physiological dead space. It maybe the cause of the change in the PA02 (under normal physiological condition). Each time you inspire or expire (humidify air) -- you lose some of that air to the dead space.

03-23-2006, 10:29 AM
Atmospheric PO2 drops from 159 to 149 as its humidified and then further drops to around 85 at the base of the lung and 136 at the apex. I thought the difference was caused by the rate of O2 uptake from blood flow, but I guess it's more so a factor of the high PCO2 in the alveoli reducing total PO2, which makes sense since there is more CO2 unloading at the base of the lung than apex. Since that's the case, I figured that if O2 is about 15% concentration at the alveoli at a PO2 of 100 mmHg, that's 15 ml/100 ml air, where as blood has a PO2 of .003 ml O2/ 100 ml blood. Since there is this discrepancy between partial pressures in liquid and air, that would demonstrate that in the 2 seconds of expiration, when only about .8 mls are taken up by the blood (from the entire lung), this wouldn't be enough of a concentration loss in the alveoli to significantly alter PO2. Is that a sensible explanation to anyone?

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