1.14.8 Pressure Volume Area Definition

Pressure Volume Area Definition is the total mechanical energy generated by the ventricle during a single cardiac cycle, encompassing both the external work performed in ejecting blood and the elastic potential energy stored within the contracted myocardium at the end of systole. Pressure–volume area is defined as the sum of ventricular stroke work, the energy expended moving blood forward, and end-systolic potential energy, the energy remaining stored in the deformed ventricular wall, and it is closely correlated with the total oxygen consumed by the myocardium during that same cardiac cycle.

Components of Pressure–Volume Area

Pressure–volume area is composed of two distinct energetic contributions generated during ventricular contraction.

External Stroke Work

External stroke work corresponds to the area enclosed by the pressure–volume loop itself, representing the mechanical energy actually transferred to the ejected blood as it is propelled into the arterial circulation.

End-Systolic Potential Energy

End-systolic potential energy corresponds to the additional area bounded by the end-systolic pressure–volume relation, the end-diastolic pressure–volume relation, and the pressure–volume loop, representing elastic energy stored within the contracted ventricular wall that is not transferred to the ejected blood but is instead dissipated as the ventricle relaxes.

Relationship to Myocardial Oxygen Consumption

Pressure–volume area has been established as a strong, nearly linear predictor of the total oxygen consumed by the myocardium during a given cardiac cycle.

Total Mechanical Energy and Metabolic Cost

Because generating both the external work of ejection and the internal potential energy of contraction requires expenditure of chemical energy by the myocardium, pressure–volume area captures the combined metabolic demand associated with a given contraction more completely than external stroke work alone.

Influence of Loading and Contractility

Because pressure–volume area combines both loop area and the region bounded by the end-systolic relation, it is sensitive to changes in preload, afterload, and contractility.

Effect of Increased Afterload

Increased afterload tends to reduce stroke volume and external stroke work while increasing end-systolic potential energy, since the ventricle contracts against greater resistance without ejecting as much blood, often leaving total pressure–volume area, and therefore oxygen demand, relatively unchanged or increased.

Effect of Increased Contractility

Increased contractility shifts the end-systolic pressure–volume relation upward, generally increasing pressure–volume area and the associated myocardial oxygen requirement for a given loading condition.

Diagrammatic Summary

Clinical Relevance

Pressure–volume area provides a physiologically grounded framework for understanding the energetic cost of ventricular contraction, offering insight into why conditions that increase afterload or contractility raise myocardial oxygen demand even when external stroke work and stroke volume do not increase proportionally, an important consideration in the management of ischemic heart disease and heart failure.