The amount of force or pressure required to expand the lungs to a given volume determines the lung compliance. A high pressure means that the lungs have a low compliance or are stiff. The two determinants of lung compliance are tissue elasticity and surface tension. Examine the contribution of tissue elasticity and surface tension to lung compliance by clicking on the saline tank or air tank to expand the lungs with saline or with air. Saline expanded lungs show only the elastic contribution because there is no air-water interface and therefore on surface tension.
Air expanded lungs show both elastic and surface tension contributions to compliance.