9.1) so that a pressure gradient or driving force is set up between the exterior and the alveoli. . . . Disruption in gas exchange due to reduction of respiratory surface area might result in respiratory failure with hypoxemia and hypercapnia. Compliance is inversely proportional to elastic recoil or elastance. Why doesn't this occur? The slope of the pressure-volume curve represents compliance. During inspiration and expiration, intrapleural pressures deviate from this resting value. Tension pneumothorax is abrupt penetration of the air into the pleural cavity which causes severe respiratory and hemodynamic compromise. Large subatmospheric mean intrathoracic pressures may be equally dangerous, perhaps by producing pulmonary oedema, but probably more importantly by reducing lung volume. the two lungs) add directly. b. . The hilar forces, the buoyancy of the lung in the pleural cavity and the different shapes of the lung and chest wall are all possible sources of local pressure differences. Resistance to air flow ("airways resistance"). . Transmural pressure gradient (alveolar distending pressure) = alveolar pressure minus intrapleural pressure. Forced inspiration causes a further increase in the volume of the thoracic space by pulling the ribs upward and outward. * During a forced expiration, intrapleural pressure actually becomes positive. A puncture of the trachea or tearing of the bronchi allows air to enter the intrapleural space during inspiration, but the air cannot be expelled during expiration, creating a tension pneumothorax. Changes in lung volume, alveolar and intrapleural pressures and airflow during the respiratory cycle (Levitzky Fig.2-5). In respect to this, what happens to intrapleural pressure during expiration? . Intrapleural pressure during a forced vital capacity (VC) maneuver is often in excess of that required to generate maximal expiratory airflow. The lungs will collapse because of their elastic recoil, and the chest wall will expand outward. . A. Frictional resistance of lung tissues and chest wall ("tissue resistance"). Higher lung volumes cause greater alveolar elastic recoil and increase the traction on small airways, distending them and decreasing airways resistance. During inspiration intrapulmonary pressure becomes less than atmospheric pressure, and during expiration it becomes greater than atmospheric pressure, according to McGraw-Hill Higher Education. f. Advantages of pulmonary surfactant are that it lowers surface tension of alveolar lining-decreases the inspiratory work of breathing and it preferentially lowers surface tension in small alveoli-stabilizes alveolar units. Thus, in the supine position the lung has less outward elastic recoil and the FRC is decreased (Levitzky Fig.2-15). . (Levitzky Fig.2-21). B. Alveolar pressure is greater than atmospheric pressure. C. Intrapleural pressure gradually falls (becomes more negative) during the expiration. a. During expiration, the thoracic wall and lungs recoil, assuming their original positions and pressures. . | 68°F. (b) passive expiration. Forced vital capacity (FVC); forced expiratory volume in first second (FEV1); forced expiratory flow rate between 25 and 75% of the vital capacity (FEF25 - 75%). N Edward Robinson, in Equine Respiratory Medicine and Surgery, 2007. Pulmonary ventilation is the process of breathing, which is driven by pressure differences between the lungs and the atmosphere. 1. "Resistive work" (Obstructive lung diseases). The views and opinions expressed in this page are strictly those of the page author. (This increases pulmonary compliance and lowers pulmonary work). 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