Obstructive sleep apnea is predominantly a disorder of overweight, middle-aged men and usually presents as excessive daytime sleepiness, a complaint that is sometimes mistaken for narcolepsy (see below). Other patients, usually those with the much-less-common central form of apnea, complain mainly of a disturbance of sleep at night, or insomnia, which may be incorrectly attributed to anxiety or depression. The occurrence of an obstructive sleep apnea is accompanied after a period of weeks or months by progressive hemoglobin oxygen desaturation, hypercapnia and hypoxia, a transient increase in systemic and pulmonary arterial pressures, and sinus bradycardia or other arrhythmias. Morning headache, inattentiveness, grogginess, and decline in school or work performance are other symptoms attributable to sleep apnea. Ultimately, systemic and pulmonary arterial hypertension, cor pulmonale, polycythemia, and heart failure may develop. When combined with obesity, these symptoms have been referred to as the “pickwickian syndrome,” so named by Burwell and coworkers, who identified this clinical syndrome with that of the extraordinarily sleepy, red-faced, fat boy described by Dickens in The Pickwick Papers.
The full-blown syndrome of obstructive sleep apnea is readily recognized by the features of daytime sleepiness, loud snoring, and the typical habitus of affected individuals. However, in patients who complain only of excessive daytime sleepiness and do not have the typical body ahbitus, the diagnosis may be elusive and require all-night polysomnographic sleep monitoring.
This disorder has been observed in patients with a variety of severe and life-threatening lower brainstem lesions—bulbar poliomyelitis, lateral medullary infarction, spinal (high cervical) surgery, syringobulbia, brainstem encephalitis, as well as with striatonigral degeneration, Creutzfeldt-Jakob disease, anoxic encephalopathy, and olivopontocerebellar degeneration. When a unilateral lesion (e.g., infarction) of the medulla is the cause, there is almost always involvement of crossing fibers between respiratory nuclei (see discussion in Chap. 25).
In addition to these symptomatic forms of sleep apnea, there is a disorder referred to as primary, or idiopathic, hypoventilation syndrome (“Ondine’s curse,” as described in Chap. 25). This last term is now applied to many forms of total loss of automatic breathing, especially during sleep. Awakenings during the night are frequent, usually after an apneic period, and insomnia is a common complaint. Snoring is mild and intermittent. In the few autopsied cases of congenital central hypoventilation of childhood, Liu and colleagues found the external arcuate nuclei of the medulla to be absent, and the neuron population in the medullary respiratory areas to be depleted.
Complex sleep apnea, or “treatment emergent central sleep apnea,” occurs most often in patients with cardiovascular conditions, particularly congestive heart failure, wherein, after sleep apnea is treated with positive airway pressure, central apnea emerges.
Treatment The approach is governed by the severity of symptoms and the predominant type of apnea, central or obstructive. In the treatment of obstructive apnea, continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BIPAP) is the most useful measure. These therapies are delivered by a tight-fitting nasal mask that is worn at night and connected to a pressure-cycled ventilator that is triggered by the patient’s breath. The increased airway pressure maintains patency of the nasoand oropharynx, thereby reducing the obstruction. A nasal device that passively resists nasal collapse by providing expiratory resistance is used by some specialists for mild sleep apnea. All of these approaches have a level of discomfort that is not tolerable to some patients.