Restrictive lung diseases are usually chronic, diffused, lung interstitial diseases, usually effecting the most peripheral and delicate interstitium of the alveolar walls.
What is pulmonary Interstitium?
Pulmonary interstitium is composed of basement membranes of the alveolar epithelial cells, vascular endothelial cells, and the tissue between them, mostly made of elastic fibers, collagen, fibroblasts that make more elastic fibers, smooth muscle cells, mast cells, and sometimes mononuclear cells.
In the peripheral parts of the lung where the alveoli are numerous the interstitium is thin and delicate. Sometimes composed of only the two basement membranes fused together.
Figure: Components of the interstitium. Note the alveolar macrophage is not a part of this interstitium. Also, in peripheral areas the interstitium is minimal causing the two basement membranes to fuse.
Hallmark of the restrictive lung diseases
Reduced compliance of the lungs. That is, the lungs are so stiff that they cannot expand easily. Patient has to exert more energy to pull air in the lungs. This is dyspnea.
Damage to the alveolar epithelium and pulmonary vessels hinders gas exchange leading to hypoxia.