06-15-2011, 02:23 PM
For =Perfusion limited ---
D= solubility---CO2 is more soluble than O2, so cross alveolar membrane quicker than O2.
P1- P2---PAo2- PaO2=100-40=60mmhg when blood FIRST enter pulmonary capillary. This gradient is drive for simple diffusion and gas equiliberate early along the lenth of the capillary.It is not diffusion limited per definition above.
For CO2, P1- P2---PACO2- PaCO2=47-40=7mmhg .Gradient is less than O2, but diffuse faster and equilibrate earlier than O2 even because D (solubility is higher than O2).
So because diffusion is not limited .So normal is perfusion limited.
Diseased lung is diffusion limited.
In diseased lung if u give pt supplemental oxygen, PAO2 increased, so gradient across membrane increased. PO2 will return to normal .Vgas (rate of gas diffusion)increase if P1- P2 increase.
D= solubility---CO2 is more soluble than O2, so cross alveolar membrane quicker than O2.
P1- P2---PAo2- PaO2=100-40=60mmhg when blood FIRST enter pulmonary capillary. This gradient is drive for simple diffusion and gas equiliberate early along the lenth of the capillary.It is not diffusion limited per definition above.
For CO2, P1- P2---PACO2- PaCO2=47-40=7mmhg .Gradient is less than O2, but diffuse faster and equilibrate earlier than O2 even because D (solubility is higher than O2).
So because diffusion is not limited .So normal is perfusion limited.
Diseased lung is diffusion limited.
In diseased lung if u give pt supplemental oxygen, PAO2 increased, so gradient across membrane increased. PO2 will return to normal .Vgas (rate of gas diffusion)increase if P1- P2 increase.