In normal respiratory function, the air flows in through the upper airway, down through the bronchi and into the lung parenchyma (the bronchioles down to the alveoli) where gas exchange of carbon dioxide and oxygen occurs. During inspiration, the lungs expand to allow airflow into the lungs and thereby increasing total volume. After inspiration follows expiration during which the lungs recoil and push air back out of the pulmonary pathway. Lung compliance is the difference of volume during inspiration and expiration.<unk>  is characterized by reduced lung volumes, and therefore reduced lung compliance, either due to an intrinsic reason, for example a change in the lung parenchyma, or due to an extrinsic reason, for example diseases of the chest wall, pleura, or respiratory muscles. Generally, intrinsic causes are from lung parenchyma diseases that cause inflammation or scarring of the lung tissue, such as interstitial lung disease or pulmonary fibrosis, or from having the alveoli air spaces filled with external material such as debris or exudate in pneumonitis. As some diseases of the lung parenchyma progress, the normal lung tissue can be gradually replaced with scar tissue that is interspersed with pockets of air. This can lead to parts of the lung having a honeycomb-like appearance. The extrinsic causes result in lung restriction, impaired ventilatory function, and even respiratory failure due to the diseases that effect the lungs ability to create a change in lung volumes during respiration due to the diseases of the systems stated above.
Restrictive lung disease
Obstructive lung disease
Alveolar lung disease
Reactive airway disease
Pulmonary heart disease
Interstitial lung disease
Asthma
Radiation-induced lung injury