Obstructive apnea is produced by structural or functional narrowing of the upper airway (Figure 20.1 A-H) or by ineffective diaphragmatic contractions that fail to create negative intrapulmonary pressure (Figure 20.1 J). Structural narrowing may occur because of a mass in, or a deformation of, the upper airways. Functional narrowing results from weak upper airway muscle contractions or lack of coordination between the diaphragmatic and upper airway muscle contractions. Functional narrowing occurs with nervous system lesions (Figure 20.1 A-E). Ineffective diaphragmatic contractions occur with loss of adhesion between the visceral and the chest wall pleura or with alveolar collapse.