1.14.5 End Systolic Pressure Volume Relation Definition

End Systolic Pressure Volume Relation Definition is the curve describing the maximum pressure a ventricle can generate at any given end-systolic volume, capturing the intrinsic contractile capability of the myocardium largely independent of the specific preload and afterload conditions under which a given contraction occurs. This relationship is constructed by plotting the end-systolic pressure and volume achieved across contractions performed under varying loading conditions, tracing the upper boundary of the ventricular pressure–volume loop and providing a load-independent measure of ventricular contractility.

Physiological Basis

The end-systolic pressure–volume relation reflects the active, force-generating capacity of the ventricular myocardium at the moment ejection ceases.

Load Independence

Because the relationship is derived from the pressure and volume achieved across a range of different loading conditions rather than from a single contraction, it isolates the intrinsic contractile state of the ventricle from the confounding effects of any one particular preload or afterload.

Approximately Linear Relationship

Across a physiological range, the end-systolic pressure–volume relation is approximately linear, allowing its position to be characterized by a slope and an intercept.

The Slope as a Contractility Index

The steepness of the end-systolic pressure–volume relation serves as a widely used index of ventricular contractility.

Elastance

The slope of this relationship is termed the end-systolic elastance, representing the ventricle's effective stiffness at the point of maximal contraction; a steeper slope corresponds to greater contractility.

Sensitivity to Inotropic State

Because the slope of the end-systolic relation changes with the contractile state of the myocardium while remaining relatively unaffected by preload or afterload alone, it provides a more specific measure of contractility than simpler indices such as ejection fraction.

Position Within the Pressure–Volume Loop

The end-systolic pressure–volume relation defines the upper-left boundary that the pressure–volume loop cannot cross during ejection.

Defining the Ejection Endpoint

As the ventricle ejects blood during systole, the trajectory of the pressure–volume loop rises until it meets this relation, at which point ejection ceases and isovolumetric relaxation begins.

Shifts With Changing Contractility

Increased contractility shifts the end-systolic pressure–volume relation upward and to the left, steepening its slope, while decreased contractility shifts it downward and to the right, flattening its slope.

Diagrammatic Summary

Clinical Relevance

Because the end-systolic pressure–volume relation isolates contractility from loading conditions, shifts in its slope are used in research and advanced clinical assessment to detect true changes in myocardial contractile function, distinguishing genuine impairment of contractility from reductions in performance caused solely by altered preload or afterload, as commonly occurs in heart failure and other cardiac conditions.