V/Q Mismatch FA page 551

[mclee0033]

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I understand the concept of V/Q mismatch. I understand the relationship between Pa and PA in the diagram on page 551 of FA. I DON'T understand the relationship between PV and Pa; why is the concentration of O2 in the pulmonary veins always less than the concentration of O2 in the pulmonary arteries? The pulmonary veins are shown as red and the arteries as blue, but even in Zone 3 O2 is shown as (in decreasing order) Pa > PV > PA

The whole point of the lungs is to oxygenate blood from the body and send it to the heart; why would the O2 content in blood leaving the lungs be lower than blood entering the lungs? I checked FA errata and this was not in it. Am I misinterpreting the diagram? Are they talking about something other than O2 content?

Can someone please help?😕

 

[RIPSanto]

I understand the concept of V/Q mismatch. I understand the relationship between Pa and PA in the diagram on page 551 of FA. I DON'T understand the relationship between PV and Pa; why is the concentration of O2 in the pulmonary veins always less than the concentration of O2 in the pulmonary arteries? The pulmonary veins are shown as red and the arteries as blue, but even in Zone 3 O2 is shown as (in decreasing order) Pa > PV > PA

The whole point of the lungs is to oxygenate blood from the body and send it to the heart; why would the O2 content in blood leaving the lungs be lower than blood entering the lungs? I checked FA errata and this was not in it. Am I misinterpreting the diagram? Are they talking about something other than O2 content?

Can someone please help?😕

That is referring to pressure. In Zone 1, the alveolar pressure is higher than the arterial pressure which is higher than the venule pressure. It is because less blood flow is going to the apex of the lung (hence a V/Q = 3 as opposed to V/Q = .6 in the base). The fact that the apex has less blood flow and still a decent ventilation causes the alveolar pressure to collapse the vessels feeding that section of lung.

Do you have access to a copy of BRS physio? I am bad at explaining as you can now see. If you can get your hands on BRS phys just read that section, it will take ten minutes.. Good luck