Lung compliance
Pulmonary compliance - is the ratio of the change in volume to the change in interpleural pressure that caused the change.
Interpleural pressure[edit | edit source]
Is the pressure between the pleurae - visceral and parietal.
- It is always negative. On inspiration: -0.8 kPa, on expiration: -0.33 kPa.
- The IPT value at resting expiration is not uniform.
- Standing examinee has IPT more negative in upper parts of lungs than in base of lungs - probably due to weight of lungs. The consequence is different ventilation of the basal and apical parts of the lungs.
- Importance of IPT negativity - keeps lungs expanded - allows chest volume changes to be monitored and thus lung ventilation is secured.
Pneumothorax[edit | edit source]
Pneumothorax is a disturbance of the pleural cavity - air is present - the lung shrinks, breathing is impaired, and hypoxia is imminent.
- Enclosed - air enters the pleural cavity from the alveolar space spontaneously or after lung injury.
- Open - when the chest wall is injured - stab wound.
- Valvular (tension) - air enters the pleural cavity with each respiratory movement but cannot escape.
Factors determining lung compliance[edit | edit source]
Elasticity of lung tissue[edit | edit source]
The lung is an elastic organ. The elasticity is due to the reticular arrangement of connective tissue. During exspiration, the fibers contract and bend. The elasticity is 1/3 of the total elasticity of the lung.
Surface tension of alveoli at the interface between alveolar air and alveolar lining[edit | edit source]
Compliance depends on the surface tension between the gas and fluid - that is, the internal surface area of the alveoli and the exchange of respiratory gases. For example, we have a bubble that is surrounded by a fluid - its surface tension will create an overpressure inside the bubble relative to the external pressure, its value determined by Laplace's law:
- If the mouth of the cylinder (ductus alveolaris) is covered by a flat soap bubble, then r is high and P is small.
When we want to increase the volume of the bubble (alveolus) we have to decrease r and thus increase P - a large opening pressure is required. Further inflation increases r and decreases P. Alveoli behave similarly. In interconnected alveoli, the smaller alveolus may shrink in favour of the larger one, but in normal lungs this is prevented by surfactant.
Surfactant[edit | edit source]
- It reduces surface tension (more in smaller alveoli than in larger alveoli). It also prevents lung collapse.
- In premature infants, the lungs have not had time to develop a functional surfactant.
- Surface tension is therefore high and atelectasis occurs → alveolar collapse → Respiratory Distress Syndrome (RDS). Lung damage also occurs with oxygen poisoning. This is partly due to oxidative destruction of surfactant.
- Compliance decreases, alveoli collapse and pulmonary edema develops.
For more information go to: Surfactant.
References[edit | edit source]
Related articles[edit | edit source]
Literature used[edit | edit source]
- SILBERNAGL, Stefan – DESPOPOULOS, Agamemnon. Atlas fyziologie člověka. 3. edition. Praha : Grada, 2004. 435 pp. ISBN 80-247-0630-X.
- GANONG, William, F. Přehled lékařské fyziologie. 1. edition. Jinočany : H & H, 1995. 681 pp. ISBN 80-85787-36-9.
- BROŽEK, Gustav – HERGET, Jan – VÍZEK, Martin. Poznámky k přednáškám z fysiologie : První díl, Dýchání, cirkulace, svaly, neurofysiologie. 1. edition. Jinočany : H & H, 1999. 229 pp. ISBN 80-86022-48-X.