Intrinsic sleep disorders:Sleep apnea
One of the most well-publicized sleep disorders is sleep apnea. Sleep apnea is defined by repetitive cessation of breathing for more than 10 seconds associated with oxygen desaturation and arousals or microarousals. These patients may awaken more than 100 times per hour and are unable to obtain quality sleep owing to the frequent arousals. These patients are generally unaware of the frequent arousals. Sleep apnea is divided into two forms, obstructive and central.
Obstructive sleep apnea
Obstructive apnea is the most common form of sleep apnea. These apneas are the result of obstruction of the upper airway. The apneas are commonly noted during stage 1, stage 2, or REM sleep. Patients are generally obese and have large necks or crowded upper airways. Some patients, however, have a normal body habitus. Bed partners generally note loud snoring and periods of apnea.
Overnight sleep studies reveal that these periods of apnea are associated with ventilatory effort but no air movement. Collapse of the upper airway occurs when the intraluminal pressures are lower than the extraluminal pressures. Commonly, structural abnormalities, such as a long soft palate or retroflexed mandible leading to a small airway, are believed to cause airway obstruction. However, for most patients with sleep apnea, the breathing disturbance is state dependent. Regulation of the airway dilator muscles comes from the nucleus solitarius and nucleus ambiguous, both of which are involved in the regulation of sleep state and respiration. Output from these nuclei can also be influenced by alcohol and muscle relaxants.
When defined as more than 5 apneas (complete absence of air movement) or hypopneas (decreased air movement) per hour, the prevalence of obstructive sleep apnea is 9% in adult women and 24% in adult men. If this frequency of apneas and hypopneas is associated with symptoms of excessive sleepiness, the prevalence is 2% in women and 4% in men.26 Long- term risks of sleep apnea include increased risk of myocardial infarction, stroke, motor vehicle accidents, hypertension, pulmonary hypertension, and right-sided heart failure.27
Central sleep apnea
Central apnea is much less common than obstructive apnea. These apneas also are associated with arousals and microarousals. Overnight sleep studies reveal periods of apnea without a ventilatory effort. Central apnea may be caused by a neurologic abnormality in the posterior fossa or other respiratory regulatory centers. Patients may have a normal body habitus.
Bed partners may note occasional snorts, but these should not be a common occurrence. If snorts or grunts at the end of the apnea periods do occur, the investigator should look for a possible obstructive component.