First of all, it is necessary to know, that "elastance" and "compliance" are strictly inverse terms.

elastance =1/sompliance

Term "elastance" means the ability of a physical body to save effort on deformation, returning this effort during shape restoration. This property is the most evident at steel springs or rubber things. Dimension of elasticity is mbar/ml, it means: how many millibars of pressure we should give a system to increase the volume by 1 ml. The term "elastance" is widely used in breath physiology trials. Nevertheless anesthesiologists use term compliance.

– Why?

– The most simple answer is: on monitors of ALV devices there's a term "compliance", so we use it.

Compliance is measured in ml/mbar. It shows, on how many milliliters the volume increases if the pressure will increase on 1 millibar. In a real clinical situation AVL measures compliance of the whole respiratory system – that is lungs and chest together. Besides Crs (compliance respiratory system) and Cst (compliance static) are synonyms. To calculate static комплайнс, the ALV device divides respiratory volume onto pressure during inspiratory pause.

Cst = VT/(Pplateau –PEEP)

Normal Cst range – 60-100 ml/mbar.

Two important tips regarding compliance:

• ALV device can measure Cst (static compliance) only during forced ventilation at completely relaxed patient in the period of ispiratory pause.
• When we speak about static compliance we analyze restrictive problems mainly connected to the state of a pulmonary parenchima.