(B) Emphysema# FACTORS AFFECTING FRC> FRC Increases with: Increased height Erect position (30% more than in supine) Decreased lung recoil (E.g. emphysema)> FRC Decreases with: Obesity, Muscle Paralysis (especially in supine) Restrictive lung disease (E.g. Fibrosis, Pregnancy) Anaesthesia FRC does not change with age> Emphysema is a condition of the lung characterized by abnormal permanent enlargement of the airspaces distal to the terminal bronchiole, accompanied by destruction of their walls and without obvious fibrosis.> Principal antielastase activity in serum and interstitial tissue is alpha 1 -AT (others are secretory leukoprotease inhibitor in bronchial mucus and serum alphal -macroglobulin), and the principal cellular elastase activity is derived from neutrophils (other elastases are formed by macrophages, mast cells, pancreas, and bacteria). Neutrophil elastase is capable of digesting human lung, and this digestion can be inhibited by alphal-antitrypsin.> The most plausible hypothesis to account for the destruction of alveolar walls is the protease-antiprotease mechanism. This hypothesis is based on two important observations, one clinical and one experimental. The first is that homozygous patients with a genetic deficiency of the protease inhibitor alphal -AT have a markedly enhanced tendency to develop pulmonary emphysema, which is compounded by smoking.# Emphysema is classified into distinct pathologic types:> The most important types being centriacinar and panacinar.# Centriacinar emphysema, the type most frequently associated with cigarette smoking, is characterized by enlarged airspaces found (initially) in association with respiratory bronchioles.> Centriacinar emphysema is most prominent in the upper lobes and superior segments of lower lobes and is often quite focal.# Panacinar emphysema refers to abnormally large airspaces evenly distributed within and across acinar units.> Panacinar emphysema is usually observed in patients with a1 AT deficiency.> Pulmonary function testing shows airflow obstruction with a reduction in FEV1 and FEV1/FVC With worsening disease severity, lung volumes may increase, resulting in an increase in total lung capacity, functional residual capacity, and residual volume.> In patients with emphysema, the diffusing capacity may be reduced, reflecting the parenchymal destruction characteristic of the disease.