Upper airway resistance syndrome

Upper airway resistance syndrome (UARS) is a sleep disorder characterized by the narrowing of the airway that can cause disruptions to sleep.

History

Upper airway resistance syndrome was first recognized at Stanford University in the late 1980s. The article that described it by name, along with its relationship to obstructive sleep apnea (OSA), was published in 1992 by Guilleminault et al.

Signs and symptoms

Symptoms of UARS are similar to those of obstructive sleep apnea, but not inherently overlapping. Fatigue, insomnia, daytime sleepiness, unrefreshing sleep, anxiety, and frequent awakenings during sleep are the most common symptoms. Oxygen desaturation is minimal or absent in UARS, with most having a minimum oxygen saturation >92%.

Many patients experience chronic insomnia that creates both a difficulty falling asleep and staying asleep. As a result, patients typically experience frequent sleep disruptions. Snoring is associated with UARS in most cases, but not always.

Some patients experience hypotension, which may cause lightheadedness, and patients with UARS are also more likely to experience headaches and irritable bowel syndrome.

A typical UARS patient is not obese and possesses small jaws, which can result in a smaller amount of space in the nasal airway and behind the base of the tongue. UARS affects equal numbers of males and females.

Diagnosis

UARS is diagnosed using the Respiratory Disturbance Index (RDI). A patient is considered to have UARS when they have an Apnea-Hypopnea Index (AHI) less than 5, but an RDI greater than or equal to 5. Unlike the Apnea-Hypopnea Index, the Respiratory Disturbance Index includes Respiratory Effort-related Arousals (RDI = AHI + RERA Index). In 2005, the definition of sleep apnea was changed to include patients with UARS by using RDI to determine sleep apnea severity.

The diagnosis of UARS is based on findings on a polysomnogram. On polysomnograms, a UARS patient will have very few apneas and hypopneas, but many Respiratory effort-related Arousals.

Portable Home Sleep Test monitors (HST) are an alternative to sleep-laboratory polysomnography. Some of the HSTs allow for the breathing signals to be viewed within the raw data of the HST study and even a cursory review of these flow signals, will reveal those patients who would likely have upper airway resistance syndrome as well. RERAs are periods of increased respiratory effort lasting for more than ten seconds and ending in arousal. Whether or not an event is classified as a RERA or Hypopnea depends on the definition of Hypopnea used by the sleep technician.

Based on symptoms, patients are commonly misdiagnosed with idiopathic insomnia, idiopathic hypersomnia, chronic fatigue syndrome, fibromyalgia, or a psychiatric disorder such as ADHD or depression. Studies show that symptoms of ADHD caused by UARS significantly improve or remit with treatment in surgically treated children.

Management

Behavioral modification

Behavioral modifications include getting at least 7–8 hours of sleep and various lifestyle changes, such as positional therapy. Sleeping on one's side rather than in a supine position or using positional pillows can provide relief, but these modifications may not be sufficient to treat more severe cases. Positive airway pressure therapy is similar to that in obstructive sleep apnea and works by stenting the airway open with pressure, thus reducing the airway resistance. Use of a CPAP can help ease the symptoms of UARS. Therapeutic trials have shown that using a CPAP with pressure between four and eight centimeters of water can help to reduce the number of arousals and improve sleepiness.

Oral appliances

Oral appliances to protrude the tongue and lower jaw forward have been used to reduce sleep apnea and snoring, and hold potential for treating UARS, but this approach remains controversial. One should also be screened for the presence of a hiatal hernia, which may result in abnormal pressure differentials in the esophagus, and in turn, constricted airways during sleep. Due to the ossification of the median palatine suture, traditional tooth-born expanders cannot achieve maxillary expansion in adults as the mechanical forces instead tip the teeth and dental alveoli. Mini-implant assisted rapid palatal expansion (MARPE) has been recently developed as a minimally invasive option for the transverse expansion of the maxilla in adults. This method increases the volume of the nasal cavity and nasopharynx, leading to increased airflow and reduced respiratory arousals during sleep.