Elastance

Elastance is a property that describes how strongly a system resists deformation in response to applied pressure or force. In mechanical and physiological contexts, elastance is defined as the change in pressure divided by the resulting change in volume, E = dP/dV. It is the reciprocal of compliance (C), where C = dV/dP. Because the physical quantities involved vary by domain, elastance is often expressed in units appropriate to the system, such as Pa per cubic meter or mmHg per milliliter in cardiovascular contexts.

In electrical engineering and related fields, elastance is used as the reciprocal of capacitance, E = 1/C. It relates voltage to charge and determines how a component resists changes in stored electrical energy.

In cardiovascular physiology, elastance is used to describe the time-varying stiffness of the heart chambers, particularly the ventricles. The instantaneous left ventricular pressure can be modeled as P(t) = E(t)[V(t) − V0], where E(t) is the time-varying elastance, V(t) is volume, and V0 is the unstressed volume. E(t) rises during systole from a minimum value (Emin, diastolic elastance) to a maximum value (Emax or end-systolic elastance, Ees). This framework underpins the pressure–volume relationship and the end-systolic pressure–volume relationship used in cardiac function assessment.

In respiratory physiology, elastance describes how airway and lung tissue resist expansion, with lung elastance equal to ΔP/ΔV and representing the inverse of lung compliance. Higher elastance means stiffer lungs and greater pressure is required to achieve a given volume change.

Elastance thus appears across disciplines as a measure of stiffness or resistance to deformation, with domain-specific definitions and applications.