Figure 2.

Proposed “vicious cycle” of acute ventilatory failure in patients with obstructive sleep apnea (OSA). Diverse acute insults may occur (eg, pulmonary embolism, infection, or abdominal surgery). Because obese patients or patients with overlap syndrome have substantial chronic respiratory loads, they develop hypoventilation with a lower degree of acute insult. OSA compounds this hypoventilation because some patients with OSA have a blunted ventilatory response to hypercapnia. As respiratory failure progresses to somnolence and exhaustion, upper airway tone is compromised, further loading the respiratory system, and reinforcing the deleterious effects of the acute load. See Figure 1 legend for expansion of abbreviations.