Sleep Disordered Breathing

Definition and Prevalence
Sleep disordered breathing (SDB) or sleep apnea is characterized by complete or partial cessation of breathing, lasting at least 10s, that occurs repeatedly throughout the night. The respiratory disturbance index (RDI) represents the number of complete pauses (apnea) and partial pauses (hypopnea) in respiration per hour of sleep.

There are two types of apnea: obstructive and central. Obstructive apneas are caused by an anatomic obstruction of the airway during sleep. Patients attempt to breathe and may appear to be choking or gasping for breath; however, despite their respiratory effort the airway is shut down. The obstruction may be located in different areas, but most often it is in the lower pharynx, between the base of the tongue and the larynx. Many patients with obstructive sleep apnea are heavy, loud snorers, as snoring in itself is also a result of a partial obstruction of airflow. In mild to moderate cases, obstructive apnea may be related to body position. Sleeping in a supine position may increase the frequency and severity of the apnea, as the tongue falls back to the anterior neck and oropharynx. Respiratory events may occur in all sleep stages; however, in some patients the length and severity of the events increases during REM sleep.

Central apneas are caused by failure of the central nervous system respiratory centers. Respiratory neurons fail to stimulate the motor neurons that activate the respiration process, resulting in an absence of respiratory effort. Central apnea is common in patients with heart failure or stroke. Many patients have mixed apneas, with both central and obstructive components.

Ancoli-Israel et al. have reported the prevalence of SDB with RDI greater than 10 in 70% of elderly men and 56% of elderly women, respectively, compared to only 15% and 5% of younger men and women, respectively.

Consequences of the Disorder
Patients with SDB stop breathing in their sleep. To start breathing again, they must awaken. Often these awakenings are so brief that they are not recalled the next morning. However, these short repetitive arousals may cause sleep fragmentation, which in turn may lead to excessive sleepiness during the day. The respiratory events may cause oxyhemoglobin desaturation, which may cause morning headaches and decreased cognitive functioning.

SDB is also an independent risk factor for hyper-tension and is associated with obesity and cardiac arrhythmias. In severe cases, SDB has been linked to increased mortality. However, in a review of the literature, Wright et al. claimed that evidence for an association between SDB and morbidity and mortality was not sound, and other confounding factors such as age, body mass index, smoking, and alcohol use were often not properly considered.