Emphysema is a disease characterized by dilation of the alveolar spaces and destruction of the alveolar walls. With their loss, much of the elastic recoil of the lung is also lost.
Compliance of the lung in emphysema is significantly above normal; the lung becomes easy to distend but empties slowly. This results in a chronically overinflated lung (high total lung capacity, functional residual capacity, and residual volume), which lessens the curvature of the diaphragm, making it less efficient in generating even the small swings in pleural pressure necessary for breathing. Pulmonary function tests on a patient with emphysema will reveal a compromised expiratory flow (due to their low lung recoil), including a low FEV1, FVC, and FEV1/FVC ratio.