Epidemiology of Lung Function and Chronic Obstructive Pulmonary Disease

Spirometry is a technique to evaluate the pulmonary ventilatory function and is a reflection of several forces implied in lung volumes. The lung volume is dependent on the elastic recoil of the lungs and chest wall and the muscular efforts of the chest wall, diaphragm, and abdomen. Contraction of the inspiratory muscles, such as the diaphragm, expands the thorax, creating an increased negative pressure. This pressure is lower than the atmospheric pressure, drawing air into the lungs. Expiration is mainly a passive process. When the muscles relax, due to elastic recoil of the lungs, air will flow out. This process can be assisted by contraction of intercostal and abdominal wall muscles, resulting in a positive pleural pressure. Using the spirogram, several different types of lung volume can be evaluated.