The clinical effects of collapse of all part of a lung depend on how much of the lung is affected. Fairly large sections of a single lung can be out of action without obvious symptoms. The term ATELECTASIS means lung collapse. There are four main causes of this condition:
1) OBSTRUCTION OF AN AIRWAY.
The amount of lung affected depends on the size of the obstructed air passage. Distal to the obstruction air is trapped and absorbed,the lung collapses and secretions collect. These may become infected,causing abscess formation. Short-term obstruction is usually followed by reinflation of the lung without lasting ill- effects. Prolonged obstruction leads to progressive fibrosis and permanent collapse.
2)IMPAIRED SURFACTANT FUNCTION.
Premature babies,may be unable to expand their lungs by their own respiratory effort because their lungs are too immature to produce surfactant. Surfactant coats the inner surface of each alveolus and reduce surface tension,allowing alveolar expansion during inspiration. These babies may need to be mechanically ventilated until their lungs begin to produce surfactant. This is called respiratory distress syndrome.
3) PRESSURE COLLAPSE.
When air or fluid enters the pleural cavity the negative pressure becomes positive,preventing lung expansion. Fluids settle in the lung bases,whereas collections of air are usually found towards the lung apex. The collapse usually affects only one lung and may be partial or complete. There is no obstruction of the airway.
4)PNEUMOTHORAX.
In this condition there is air in the pleural cavity. It may occur spontaneously or be the result of trauma.
