science

Upper airway resistance syndrome

Upper airway resistance syndrome is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Upper airway resistance syndrome rather than just read about it. In short: Upper airway resistance syndrome (UARS) is a sleep disorder characterized by the narrowing of the airway that can cause disruptions to sleep. The symptoms include snoring, unrefreshing sleep, nocturia, fatigue, sleepiness, chronic insomnia, and difficulty concentrating.

Key takeaways

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Reproduce the core statement of Upper airway resistance syndrome from memory before moving on to harder problems.

Reference excerpt

Upper airway resistance syndrome (UARS) is a sleep disorder characterized by the narrowing of the airway that can cause disruptions to sleep. The symptoms include snoring, unrefreshing sleep, nocturia, fatigue, sleepiness, chronic insomnia, and difficulty concentrating. UARS can be diagnosed by polysomnograms capable of detecting Respiratory Effort-related Arousals. It can be treated with lifestyle changes, functional orthodontics, surgery, mandibular repositioning devices or CPAP therapy. UARS is considered a variant of sleep apnea, although some scientists and doctors believe it to be a distinct disorder.

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. Predisposing factors include a high and narrow hard palate, an abnormally small intermolar distance, an abnormal overjet greater than or equal to 3 millimeters, and a thin soft palatal mucosa with a short uvula. In 88% of the subjects, there is a history of early extraction or absence of wisdom teeth. There is an increased prevalence of UARS in east Asians.

Pathophysiology Upper airway resistance syndrome is caused when the upper airway narrows without closing. Consequently, airflow is either reduced or compensated for through an increase in inspiratory efforts. This increased activity in inspiratory muscles leads to the arousals during sleep which patients may or may not be aware of. 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. Patients may have other anatomical abnormalities that can cause UARS such as deviated septum, inferior turbinate hypertrophy, a narrow hard palate that reduces nasal volume, enlarged tonsils, or nasal valve collapse. UARS affects equal numbers of males and females. Why some patients with airway obstruction present with UARS and not OSA is thought to be caused by alterations in nerves located in the palatal mucosa. UARS patients have largely intact and responsive nerves, while OSA patients show clear impairment and nerve damage. Functioning nerves in the palatal mucosa allow UARS patients to more effectively detect and respond to flow limitations before apneas and hypopneas can occur. Patients with intact nerves are able to dilate the genioglossus muscle, a key compensatory mechanism utilized in the presence of airway obstruction. What damages the nerves is not definitively known, but it is hypothesized to be caused by the long term effects of gastroesophageal reflux and/or snoring.

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. The American Academy of Sleep Medicine currently recognizes two definitions. The scoring of Respiratory Effort-related Arousals is currently designated as "optional" by the AASM. Thus, many patients who receive sleep studies may receive a negative result, even if they have UARS. 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 have found that children with UARS are frequently misdiagnosed with ADHD. One study found UARS or OSA present in up to 56% of children with ADHD. 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. Avoiding sedatives including alcohol and narcotics can help prevent the relaxation of airway muscles, and thereby reduce the chance of their collapse. Avoiding sedatives may also help to reduce snoring.

Medications Nasal steroids may be prescribed in order to ease nasal allergies and other obstructive nasal conditions that could cause UARS.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Upper airway resistance syndrome

Start with the simplest possible case. Write down what Upper airway resistance syndrome claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Upper airway resistance syndrome before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Upper airway resistance syndrome ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Upper airway resistance syndrome

In research: Upper airway resistance syndrome appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Upper airway resistance syndrome in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Upper airway resistance syndrome is common in secondary-school and first-year university syllabi. It links to neighbouring topics Breathing abnormalities, Sleep disorders, Sleep physiology, so understanding it makes those chapters shorter.
In everyday life: Look for Upper airway resistance syndrome outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Upper airway resistance syndrome in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Upper airway resistance syndrome means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Upper airway resistance syndrome out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Upper airway resistance syndrome in simple terms?

Why does Upper airway resistance syndrome matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Upper airway resistance syndrome?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Upper airway resistance syndrome.