Restrictive lung diseases (or restrictive ventilatory defects) are a category of extrapulmonary, pleural, or parenchymal respiratory diseases that restrict lung expansion, resulting in a decreased lung volume, an increased work of breathing, and inadequate ventilation and/or oxygenation. Pulmonary function test demonstrates a decrease in the forced vital capacity.
In disorders that are intrinsic to the lung parenchyma, the underlying process is usually pulmonary fibrosis (scarring of the lung). As the disease progresses, the normal lung tissue is gradually replaced by scar tissue interspersed with pockets of air. This can lead to parts of the lung having a honeycomb-like appearance.
In restrictive lung disease, both forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) are reduced, however, the decline in FVC is more than that of FEV1, resulting in a higher than 80% FEV1/FVC ratio. In obstructive lung disease however, FEV1 is reduced while FVC remains stable, consequentially depicting a lower FEV1/FVC ratio.