QS Study

Lung Compliance

Definition: The expansibility of lungs and thorax is called compliance. It is basically the relationship between how much pressure is required to generate a degree of volume change of the lungs. It is affected by the elastic properties of the lung, which are reduced in emphysema, where lung compliance is high.

  • It is expressed as the volume increase in the lungs for each unit; increase in alveolar pressure or for each unit decrease in plural pressure.
  • The combined compliance of lungs and thorax is 0.13 L/cm of H2O pressure.
  • The compliance of lungs alone after removal from the chest is about 0.22 L/cm of H2

Lung compliance can be reduced in diseases such as idiopathic pulmonary fibrosis, where the elastic fibers of the lung (elastin) are replaced by stiffer collagen. Patients with decreased lung compliance need to work harder in order to breathe.

Factors those cause abnormal compliance

The compliance of the lung describes the connection between the transmural pressures across the lung compared with organ’s volume. By transmural pressure, we mean the relative pressure between the alveoli compared with that in the intrapleural space. Positive transmural pressures mean greater alveolar pressures than intrapleural pressures.

  • Any condition that destroys the lung tissue decrease compliance.
  • Deformities of chest such as kyphosis, silicosis diseases lung compliance.
  • Fibrotic pluralism paralyzed muscle reduces the chest compliance.