Upper airway resistance syndrome

Upper airway resistance syndrome or UARS is a sleep disorder characterized by airway resistance to breathing during sleep. The primary symptoms include daytime sleepiness and excessive fatigue.

Polysomnography (sleep study) with the use of a probe to measure Pes (esophageal pressure) is the gold standard diagnostic test for UARS. Apneas and hypopneas are absent or present in low numbers. Multiple snore arousals may be seen, and if an esophageal probe (Pes) is used, progressive elevation of esophageal pressure fluctuations terminating in arousals is noted. UARS can also be diagnosed using a nasal cannula/pressure transducer to measure the inspiratory airflow v. time signal.

During sleep the muscles of the airway become relaxed. The relaxation of these muscles in turn reduces the diameter of the airway. Typically, the airway of a person with UARS is already restricted or reduced in size, and this natural relaxation reduces the airway further. Therefore, breathing becomes labored. It can be likened to breathing through a straw.

Pathophysiology of UARS is similar to obstructive sleep apnea / hypopnea syndrome in that abnormal airway resistance in the upper airway during sleep leads to unwanted physiologic consequences. Increased upper airway resistance in this disorder does not lead to cessation of airflow (apnea) or decrease in airflow (hypopnea), but instead leads to an arousal secondary to increased work of breathing to overcome the resistance. Repeated and multiple arousals (of which the person is usually unaware) result in an abnormal sleep architecture and daytime somnolence (sleepiness). Arousals result in sympathetic activation, and UARS is therefore likely to cause hypertension similar to obstructive sleep apnea syndrome (This has not been verified in large clinical populations because of the relatively small number of people with UARS in the larger epidemiologic studies so far. However, repeated arousals in individuals have clearly been shown to be related to sympathetic activation and elevation in blood pressure).

People with UARS present with snoring and excessive daytime somnolence. Hypotension is likely to be present. Also, fatigue, cognitive impairment, unrefreshing sleep, frequent awakenings, and chronic pain may be present.

UARS is often misdiagnosed as fibromyalgia or similar disorders. Guilleminault et al. write that up to 75% of adults with sleepwalking have UARS.

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