An understanding of the physiological processes underlying respiratory function in the healthy individual is essential in recognising and understanding disease processes. Departure from the normal pattern of tidal breathing is an early and reliable sign of respiratory disease. Understanding the normal distributions of pressures within the thoracic cage, airways and lungs allows one to predict the site of airway obstruction. Respiratory signs and symptoms are based on alterations of normal physiology by the disease process. Unfortunately, these basic principals are rarely emphasised in current teaching programs. (C) 2006 Elsevier Ltd. All rights reserved.