Atelectasis
Atelectasis refers either to the incomplete expansion of neonatal lungs or to the collapse of previously inflated lungs.
Resorption atelectasis results from complete obstruction of the airways without impairment of blood flow. Air is resorbed from blocked alveoli and lung volume shrinks. This shifts the mediastinum towards the site of collapse. It is commonly caused by the mucous plugs accompanying asthma, chronic bronchitis, bronchiectasis, postoperative states, and foreign body aspiration.
Compression atelectasis follows from filling of the pleural cavity with fluid, tumour, blood, or air (pneumothorax). It is most common in people with heart failure who develop pleural fluid. The mediastium shifts away from the affected lung.
Contraction atelectasis occurs when fibrosis of the lung or pleura prevent full expansion. This is the only kind which is not reversible.