ABSTRACT
The principles of air movement into and out of the lung are the principles of physics. Air passively follows gradients of pressure established by the respiratory system. The chest wall serves as the supporting structure and pump of the respiratory system and the lung as the conduit for air movement and the interface for gas exchange. Both gravity and regional differences in resistance and compliance influence the distribution of air within the lung during inspiration. Some of the inspired air is necessarily wasted in the physiologi cal dead space. During expiration, several factors influence expiratory airflow, with airflow
limitation leading to significant problems associated with air trapping and hyperinflation. All of these factors combine to influence gas exchange and determine the ultimate work of breathing-endpoints that may be altered in various disease states. From these principles, symptoms and signs of pulmonary disease based on the alteration of movement of air into and out of the lung are better understood.
