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 USMLE Step 1 Bits & Pieces High yield short focused points, monographs, charts, illustrations, tables, and other stuff related to the USMLE Step 1 Exam.

#1
08-21-2009
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 3,317 Threads: 170 Thanked 4,879 Times in 1,808 Posts Reputation: 4932
Pressure Volume Loops

Cardiac ventricular pressure volume loops are 100% seen in step 1 USMLE exams so a good grasp of the concept will yield points on the day.
Here's a simple graph that I drew, click thumbnail to enlarge

The Y axis is the LV Pressure and the X axis is the LV Volume
Point A:
Represent mitral valve closure.
A line drawn from point A to X axis will cross the x aixs at the End Diastolic Volume EDV while the dotted line drawn from point A to the Y axis will cross it at the End Diastolic Pressure EDP.
A shift of point A to the right means more EDV and so more Preload.
The straight vertical line between A and B represent isovolumetric contraction.

Point B:
Represent Aortic Valve Opening.
It also corresponds to the Diastolic Pressure if a horizontal line drawn toward the Y axis.
The diastolic pressure is good indicator of the overall resistance of the system.
The dome line from B to C is simply the ejection phase and it's peak point represent the systolic pressure on the Y axis.

Point C:
Represent Aortic Valve Closure.
It also corresponds to the End Systolic Volume ESV.
Therefore the width of the loop is simply the stroke volume as it equals to EDV-ESV.
The vertical line from C to D is the isovolumetric relaxation.

Point D:
Represent Mitral Valve Opening, where pressure nears zero
The rising line thereafter is simply the filling phase.

Slopes:
The slope drawn from the 50 ml volume to point C and beyond represents the contractility. In other words, how quickly the pr changes for a given change in volume.
Shifting this slope to the left means increased contractility. Shifting this slope to the right (down) means decreased contractility.

The other horizontal slope (from 50 to point A) represent the compliance. In other words, how quickly the volume changes for a given pressure.
Steep curves means low compliance (for example ventricular hypertrophy). Flat curves means high compliance (for example ventricular dilatation).

Last edited by Sabio; 08-22-2009 at 09:58 AM.
 The above post was thanked by: erickven (04-28-2016), Gulara (08-19-2011), memory (12-26-2009), pukhtoon123 (11-30-2013), q172278932 (06-12-2016), Taiwan_Guy (05-19-2011)

#2
08-21-2009
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 3,263 Threads: 147 Thanked 4,993 Times in 1,563 Posts Reputation: 5089

Thanks Sabio for such a thorough explanation
#3
12-26-2009
 USMLE Forums Scout Steps History: --- Posts: 11 Threads: 2 Thanked 3 Times in 2 Posts Reputation: 13

this is very simplified explanation, and causes an immediate clearing off of the clouds of confusion. thank you very much.
#4
08-06-2011
 USMLE Forums Guru Steps History: --- Posts: 332 Threads: 48 Thanked 168 Times in 107 Posts

Sabio did a wonderful job on presenting the normal pressure-volume loop, here is the link ofr abnormal pressure-volume loops http://www.cvphysiology.com/Heart%20Disease/HD009c.htm

Last edited by usluipek; 08-06-2011 at 02:07 PM.
 The above post was thanked by: paperplane (11-08-2016)

 Tags Cardiovascular-, Figures-, Physiology-

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