Pathophysiology of central sleep apneas.

The transition from wake to sleep is accompanied by a host of physiologic changes, which result in major alterations in respiratory control and may result in sleep-related breathing disorders. The central sleep apneas are a group of sleep-related breathing disorders that are characterized by recurrent episodes of airflow reduction or cessation due to a temporary reduction or absence of central respiratory drive. The fundamental hallmark of central sleep apnea (CSA) disorders is the presence of ventilatory control instability; however, additional mechanisms play a role in one or more specific manifestations of CSA. CSA may manifest during conditions of eucapnia/hypocapnia or chronic hypercapnia, which is a useful clinical classification that lends understanding to the underlying pathophysiology and potential therapies. In this review, an overview of normal breathing physiology is provided, followed by a discussion of pathophysiologic mechanisms that promote CSA and the mechanisms that are specific to different manifestations of CSA.