Pressure volume diagram
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A pressure volume diagram (or P-V diagram, or volume-pressure loop)[1]) is used to describe a thermal cycle involving the following two variables:
- Volume (on the X axis)
- Pressure (on the Y axis)
This is in fact enough information to fully describe a simple system from a thermodynamic standpoint. The diagrams are useful when one wants to calculate the work done by the system, the integral of the pressure with respect to volume. One can often quickly calculate this using the PV diagram as it is simply the area enclosed by the cycle.
In the heart
In cardiovascular physiology, the diagram is often applied to the left ventricle, and it can be mapped to specific events of the cardiac cycle. The flow of events is as follows, and in the opposite direction to the diagram above (counterclockwise). See external links for a much more precise representation:
| ejection - horizontal line | ||
| isovolumetric relaxation - vertical line | isovolumetric contraction - vertical line | |
| diastole - horizontal line |
The two vertical lines are usually much more straight than the two horizontal lines. The distance between the two vertical lines is the stroke volume.[1]
A line tangent to the end of the ejection phase (the upper left hand corner) can be used to estimate inotropic state.[1]. (It is easier to identify this line when multiple consecutive cycles are plotted on top of each other.)
See also
References
Additional Resources
- Lohff B (1999). "1899: the first mathematical description of the pressure-volume diagram by Otto Frank (1865-1944)". Sudhoffs Arch 83 (2): 131-51. PMID 10705804.
External links
Cardiovascular system, physiology: cardiovascular physiology | |
|---|---|
| Volumes | Preload - Afterload - End-systolic volume - End-diastolic volume - Frank-Starling law of the heart |
| Interactions | Cardiac output - Wiggers diagram - Pressure volume diagram |
| Tropism | Chronotropic - Dromotropic - Inotropic |
| Hemodynamics | Baroreflex - Kinin-kallikrein system - Renin-angiotensin system - Vasoconstrictors - Vasodilators - Compliance - Vascular resistance |
| Other | Electrical conduction system of the heart (Cardiac action potential) |
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
