Using the pathophysiology of obstructive sleep apnea to teach cardiopulmonary integration

Department of Physiology, Louisiana State University Health Sciences Center, New Orleans, Louisiana Address for reprint requests and other correspondence: M. G. Levitzky, Dept. of Physiology, Box P7-3, Louisiana State Univ. Health Sciences Center, 1901 Perdido St., New Orleans, LA 70112-1393 (e-mail: mlevit{at}lsuhsc.edu ) Abstract Obstructive sleep apnea (OSA) is a common disorder of upper airway obstruction during sleep. The effects of intermittent upper airway obstruction include alveolar hypoventilation, altered arterial blood gases and acid-base status, and stimulation of the arterial chemoreceptors, which leads to frequent arousals. These arousals disturb sleep architecture and cause hypersomnolence. Chronic intermittent alveolar and systemic arterial hypoxia-hypercapnia can cause pulmonary and systemic hypertension, with effects on the right and left ventricles, and even the renal system. The pathophysiology of OSA can therefore be used to review and integrate many topics in pulmonary and cardiovascular physiology in the context of problem-based learning, a guided discussion, or a formal lecture. The discussion begins with a case scenario, followed by a definition of the disorder, the common symptoms and signs of OSA, and a description of an apneic event. These are related to the physiology of the upper airway in OSA, normal alterations in the respiratory system during sleep, the effects of apnea on gas exchange and arterial blood gases, and the cardiovascular consequences of alterations in alveolar and systemic arterial P O 2 and P CO 2 . The treatment of OSA, particularly how the use of continuous positive airway pressure relates to the pathophysiology of the disorder, is discussed briefly. Key words: mechanics of breathing; alveolar hypoventilation; pulmonary hypertension; systemic hypertension