# Pressure, Volume, and Compliance curves

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#### stronghold

##### Full Member
5+ Year Member

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I encountered two unrelated UW questions that made me confused. I drew them- I apologize for bad drawing but this is what I can do with Paint app. The first diagram is for lung. The second one, please notice that axis are paradoxical, is for mitral regurgitation. UW states that the curve 1, in the 2nd diagram, is acute MR with normal compliance, so more prone to have acute pulmonary edema. While the curve 2 has high compliance (as stated by UW).

I don't understand the way of compliance curves in both diagrams. I hope you can help me to understand those curves and the meaning of compliance in both of them.

Last edited:

5+ Year Member
Up!

#### paul411

##### ANES
7+ Year Member
Compliance = ability to stretch

Interpreting the graphs
What you are looking for: for a given change in volume, how much does the pressure change.
How to compare the two lines on each graph: if the change in pressure is high for the same change in volume, this indicates lower compliance (less ability to stretch, like a fibrosed lung)

Curve 2 (blue) has a lower compliance (not higher as you stated in your post) because for the same increase in volume between curves 1 and 2, the increase in pressure is much higher for Curve 2 (blue) which means that it is less compliant.

#### stronghold

##### Full Member
5+ Year Member
Gotcha. Thanks man! Oh, UW states curve two has to increase compliance, but I wrote it high compliance. My bad!

#### Shunnar

##### Full Member
As far as I know:
Good compliance is that variation in volume does not affect pressure significantly...bad complaince is the opposite
So in the second one, curve 2 has lower complaince because the change in volume made it increase pressure highly..
Complaince is inversly proportional to the slope of the volume-pressure curve

#### ChessMaster3000

##### Full Member
10+ Year Member
Also related to this concept is that of elastance, which is 1/compliance