Elastance

Elastance is a measure of the opposition to deformation or the tendency of an object or substance to return to its original shape after being deformed. It is the reciprocal of compliance. In other words, elastance measures the pressure change required to produce a specific volume change. A material with high elastance requires a large pressure change to produce a small volume change, indicating stiffness. Conversely, a material with low elastance requires only a small pressure change to produce the same volume change, indicating pliability or distensibility.

Elastance is particularly relevant in physiology, especially in the study of the respiratory system and cardiovascular system. For example, lung elastance refers to the lungs' ability to recoil after inflation. A higher lung elastance means the lungs are stiffer and require more effort to inflate. Similarly, in the cardiovascular system, arterial elastance refers to the stiffness of the arteries. Increased arterial elastance can contribute to high blood pressure.

Mathematically, elastance (E) is defined as:

E = ΔP / ΔV

Where:

• ΔP is the change in pressure
• ΔV is the change in volume

The units of elastance are typically pressure units per volume unit, such as cm H2O/L (centimeters of water per liter) or mmHg/mL (millimeters of mercury per milliliter).

While closely related to elasticity, elastance, as used particularly in physiology, often reflects a more complex, system-level property incorporating both elastic and viscous elements of the tissue or structure in question. Thus, it represents a more practical, overall measurement of stiffness under dynamic conditions compared to solely static elasticity measurements. Pathological conditions can often affect elastance measurements, providing diagnostic value.