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Figure 1: Idealized pressure–volume diagram featuring cardiac cycle components. Real-time left ventricular (LV) pressure–volume loops provide a framework for understanding cardiac mechanics in experimental animals and humans.
A pressure–volume diagram (or PV diagram, or volume–pressure loop) [1] is used to describe corresponding changes in volume and pressure in a system. They are commonly used in thermodynamics , cardiovascular physiology , and respiratory physiology .
Pressure–volume loops are widely used in basic and preclinical research.Left ventricular PV loops are considered to be the gold standard for hemodynamic assessment and are widely used in research to evaluate cardiac performance.
Because the net variation in state properties during a thermodynamic cycle is zero, it forms a closed loop on a P-V diagram. A P-V diagram's abscissa, Y axis, shows pressure (P) and ordinate, X axis, shows volume (V). The area enclosed by the loop is the net work done by the processes, i.e. the cycle:
(See gray and light-blue tracings labeled "atrial pressure" and "ventricular pressure"—Wiggers diagram.) Here also may be seen the red-line tracing of "Ventricular volume", showing an increase in blood volume from the low plateau of the "isovolumic relaxation" stage to the maximum volume occurring in the "atrial systole" sub-stage. [1] [2]
His data was analyzed on a pressure-volume diagram, which resulted in his description of peak isovolumic pressure and its effects on ventricular volume. [ 5 ] Starling experimented on intact mammalian hearts, such as from dogs, to understand why variations in arterial pressure, heart rate, and temperature do not affect the relatively constant ...
The discontinuity in , and other properties, e.g. internal energy, , and entropy,, of the substance, is called a first order phase transition. [12] [13] In order to specify the unique experimentally observed pressure, (), at which it occurs another thermodynamic condition is required, for from Fig.1 it could clearly occur for any pressure in the range .
A pressure/volume graph of the idealized Stirling cycle. In real applications of the Stirling cycles (e.g. Stirling engines) this cycle is quasi-elliptical. The idealized Stirling [5] cycle consists of four thermodynamic processes acting on the working fluid (See diagram to right):