TITLE: Obstructive Sleep Apnea Syndrome
SOURCE: Dept. of Otolaryngology, UTMB, Galveston, TX
DATE: February 4, 1998
RESIDENT PHYSICIAN: Robert H. Stroud, M.D.
FACULTY PHYSICIAN: Francis B. Quinn, Jr., M.D.
SERIES EDITOR: Francis B. Quinn, Jr., M.D.

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"This material was prepared by physicians in partial fulfillment of educational requirements established for Continuing Postgraduate Medical Education activities and was not intended for clinical use in its present form. It was prepared for the purpose of stimulating group discussion in a interactive computer mediated conference setting. No warranties, either express or implied, are made with respect to its accuracy, completeness, or timeliness. The material does not necessarily reflect the current or past opinions of subscribers or other professionals and should not be used for purposes of diagnosis or treatment without consulting appropriate literature sources and informed professional opinion."


HISTORY

The symptoms of obstructive sleep apnea syndrome (OSAS) have been recognized for many years. Charles Dickens' description of an obese, hypersomnolent boy in The Pickwick Papers is a classic portrayal. William Osler also noted the association of obesity and hypersomnolence when he described the obesity-hypoventilation syndrome or Pickwickian syndrome in 1918. Despite some interest and research, it was not until 1973 that Guilleminault described the obstructive sleep apnea syndrome. Since that time, much research has been performed with some increased understanding of the pathophysiology and treatment of the disorder. The most widely applied surgical procedure for the treatment of OSAS in adults, the uvulopalatopharyngoplasty (UPPP), was described in 1981 by Fujita. More recently, nasal continuous positive airway pressure (CPAP) has been found to be an effective non-surgical treatment for the disorder and is widely used in its treatment.

EPIDEMIOLOGY

It has been previously reported that 85% of OSAS patients are men. More recent studies have shown that the prevalence of the disorder among women is 2%, which is higher than was expected, and 4% in men. Approximately 2/3 of affected patients are obese. OSAS is more common in elderly patients and it has been shown to occur more frequently among African-Americans.

PATHOPHYSIOLOGY

OSAS is caused by an increased propensity for upper airway collapse during sleep. Much of the airway is supported by a bony or cartilaginous framework, but the dual function of the pharynx as both a conduit for deglutition and ventilation necessitates that its walls be muscular and thus compliant and collapsible. During inspiration, negative pressure is generated within the airway by the action of the respiratory muscles. Air flow is governed by the Bernoulli principle and the Venturi effect. The Bernoulli principle states that a column of air flowing through a conduit produces a partial vacuum or negative pressure at the margins of the column. This negative pressure increases as the rate of flow increases. The Venturi effect describes the acceleration of flow as a current of air or liquid enters a narrowed passage. These forces act upon the pharyngeal walls during inspiration to promote collapse of the airway.

In the normal airway, the negative pressure created by inspiration is counteracted by tone of the upper airway musculature thereby maintaining airway patency. The resistance met by the airflow may induce vibrations within the pharyngeal walls which is manifested as snoring. Over time, the vibrations transmitted through the pharyngeal mucosa and musculature lead to tissue laxity with the formation of redundant folds of mucosa which further impinges upon an already narrow airway. This is often compounded by the deposition of adipose tissue around the airway which has been shown to occur in obesity. In addition, it has been shown by detailed cephalometric examination that patients with OSAS are more likely to have definable skeletal and soft tissue abnormalities which narrow their upper airway. It is likely that there is an interaction between anatomic abnormalities and dysfunction of the upper airway musculature during sleep that leads to collapse of the airway and obstruction.

It has been demonstrated that the electrical activity within upper airway muscles, particularly the genioglossus and tensor palatini, is increased in persons with OSAS while awake, likely in compensation for the anatomic abnormalities which render the airway more susceptible to collapse. This increased electrical activity is noted to decrease with the onset on sleep however, making collapse of the pharyngeal walls more likely. Many patients with some increased risk for airway collapse are able to maintain their airways during the early stages of sleep while the musculature of the upper airway maintains adequate tone, but with the onset of REM sleep and associated decrease in pharyngeal muscle tone, the airway collapses. This tendency is compounded with the use of alcohol or other sedatives. With prolonged collapse despite continued respiratory effort, the patient's oxyhemoglobin saturation level decreases while carbon dioxide levels rise. This leads to some level of arousal into the earlier stages of sleep and a concurrent increase in upper airway muscle tone and restoration of upper airway patency. This cycle continues throughout the night with periodic arousals and sleep fragmentation leading to the main symptom of the disorder - daytime hypersomnolence.

However, the cycle induces physiologic changes in addition to the sleep fragmentation. Many patients exhibit polycythemia as a result of decreased oxyhemoglobin levels. The hypercapnia induces pulmonary vasoconstriction and chronically may lead to pulmonary hypertension, right heart failure and cor pulmonale. It has also been hypothesized that this cycle induces systemic hypertension and thus accounts for an increased incidence among OSAS patients (50%) with all its accompanying complications. Patients also may demonstrate arrythmias in response to the decreased oxygenation resulting from the obstruction, some of which may be lethal. It is plain that the result of recurrent upper airway obstruction is quite devastating with potentially serious complications, both immediately and long-term.

EVALUATION

The evaluation of a patient suspected of having OSAS begins of course with a complete history and physical examination. The most common and important symptoms suggesting OSAS are snoring and daytime sleepiness. It may be helpful to question the patient's sleeping partner as to the patient's sleep and snoring patterns. It is important to attempt to characterize the snoring as intermittent, continuous or occurring only in certain positions. The characteristic pattern of snoring in OSAS is prolonged periods of respiratory effort without airflow, punctuated by loud, snorting episodes with some level of arousal.

Hypersomnolence is the other key feature of OSAS in adults. Many patients describe sleepiness occurring with a decrease in physical activity, such as while reading or driving, and often attribute it to boredom. Excessive sleepiness may make driving quite hazardous and some patients may give a history of frequent motor vehicle accidents. Some are reluctant to reveal their inability to drive without lapsing into a slumber as they are fearful that it will interfere with the carrying out of their job requirements. Other symptoms suggestive of OSAS may be attained during a thorough history. These include physically restless sleep, personality changes, morning headaches, impaired cognitive skills, morning confusion, nocturia or nocturnal enuresis and sexual dysfunction. Patients may also report recent weight gain coinciding with the onset of symptoms. A history of the use of alcohol, sedatives or other medications may also be elicited and often patients notice that their symptoms increase with their use.

There are many conditions which may be associated with OSAS. A complete evaluation should focus on signs or symptoms of these conditions as correction of these disorders may improve the outcome of any treatment. Associated conditions include: adenotonsillar hypertrophy, nasal obstruction, hypothyroidism, acromegaly, Down syndrome, micrognathia, retrognathia and obesity. Masses within the head and neck or vocal cord paralysis may also induce obstruction.

The physical examination begins with a general inspection of the patient's appearance. Retrognathia may be quickly identified as may an associated obtuse cervicofacial angle. Mouth-breathing indicative of chronic nasal obstruction may also be obvious. A general "tired" appearance may be recognized as bloodshot, protuberant eyes. Examination of the nose and nasal cavity may reveal such anatomic abnormalities as turbinate hypertrophy, septal deviation or nasal polyposis. While nasal obstruction alone does not cause OSAS, the mouth breathing associated with the obstruction causes the mandibular angle and base of tongue to be retro-placed thus narrowing the airway and increasing the likelihood of airway compromise. Examination of the oral cavity and oropharynx often reveals characteristic findings. These include redundant folds of mucosa on the palate and in the oropharynx with thickened, beefy red mucosa. Patients with OSAS also may have an elongated uvula and exhibit a prominent gag reflex. Retrognathia, micrognathia or macroglossia may be identified, as well as relative tonsillar hypertrophy with a noticeable decrease in the caliber of the airway. Plainly stated, there appears to be too much tissue for the space available.

Evaluation of the airway should include fiberoptic endoscopy. Special attention should be given to attempting to localize the site of obstruction. This is a difficult task as the obstruction usually occurs in multiple sites, with no one clear identifiable lesion. Mueller's maneuver, which is performed by having the patient inhale with the nasal passages occluded and the lips closed while examining the airway, is often helpful in ascertaining the level of greatest obstruction. It should be performed several times with the tip of the endoscope at various levels within the airway. It may also give some further insight as to the level of obstruction to perform the examination with the patient lying supine. As stated previously, it is uncommon for there to be a specific site of obstruction identified on examination, but multiple factors which attribute to the tendency for airway collapse may be recognized.

If the diagnosis of OSAS is suspected based upon the history and physical findings, the diagnosis and evaluation of the severity of the disorder is best assessed by polysomnography, commonly referred to as a sleep study. A complete polysomnogram includes an electroencephalogram for sleep staging, bilateral electro-oculograms, submental electromyogram, nasal and oral air flow, respiratory muscle movement or effort, oxygen saturation, electrocardiogram, anterior tibialis electromyogram and sleep position. The study should be completed during the patient's normal sleep time and should include a minimum of two to four hours of sleep.

The polysomnogram is diagnostic for sleep apnea and can differentiate between central, obstructive or mixed apneic episodes. It may also diagnose periodic leg movement during sleep (PLMS) based upon the EMG tracing from the anterior tibialis or may suggest the diagnosis of narcolepsy if a decreased sleep latency is noted. Several definitions should be understood in order to properly interpret a polysomnogram. Sleep apnea is defined as the cessation of airflow due to obstruction or cessation of respiratory effort. An apneic episode is defined as the cessation of airflow for ten seconds and an hypopnea is defined as a 50% decrease in flow or any decrease in breathing that leads to EEG arousal. Apneic or hyponeic episodes may be characterized as central, obstructive or mixed. Central apneas occur with a cessation of respiratory effort while obstructive apneas occur due to airway obstruction despite continued respiratory effort. Mixed apneas typically begin with a decrease in respiratory effort as in central apnea, but terminate with airway obstruction as in obstructive apnea.

The severity of the disorder and the expected symptomatology may be predicted based on several values derived from the sleep study. The apnea/hyponea index, or respiratory disturbance index (RDI) is defined as the number of events occurring per hour of sleep. A normal study is characterized by a value less than 5, while most clinically significant studies and symptomatic patients will exhibit a value greater than or equal to 20 events per hour. Severe OSAS is characterized by greater than 80 events per hour. Also of use in predicting disease severity is the apnea duration and degree of desaturations. Desaturations to a value less than 80% are definitely significant while values less than 90% may be significant. The use of the sleep disturbance index, or the number of arousals per hour of sleep may also have some correlation with symptomatology.

A therapeutic polysomnogram may be attained which measures the same variables with the patient utilizing CPAP. The amount of pressure applied to the airway may be adjusted while the patient is asleep and monitored to assure adequate splinting of the airway to prevent collapse and thus attain relief of the obstruction. Repeat studies may be attained after other interventions to assess their effectiveness in decreasing the apnea/hyponea index.

A number of radiographic studies have been advocated for the evaluation of OSAS to aid in localizing the site of obstruction. In children, a lateral neck film may give much information on the degree of airway narrowing due to adenotonsillar hypertrophy and is quite readily attained and interpreted. Computed tomography and magnetic resonance imaging have shown some usefulness in localizing the likely site of obstruction, but add little guidance for treatment decisions. Somnofluoroscopy has the advantage of a real time examination of the airway, but is often difficult to perform. Some authors have recommended that a detailed cephalometric examination be performed on each patient before any surgical intervention is attempted. These radiographs and their interpretation may suggest the need for procedures that alter the geometry of the facial and airway skeletal support in order to relieve the obstruction.

Other investigations which may be useful include thyroid function tests in order to rule out occult hypothyroidism, arterial blood gas to assess for acid-base disorders resulting from the apneic episodes and complete blood count to diagnose reactive polycythemia. A chest radiograph and electrocardiogram may reveal right heart failure and cor pulmonale resulting from chronic pulmonary vasoconstriction. Audio or audio-visual recordings of the patient's sleep can be useful in children where the diagnosis and treatment are often less involved. Rhinomanometry may quantify the degree of nasal obstruction.

If central apneas are identified on the polysomnogram, radiographic imaging of the brain and brainstem may be indicated in order to rule out any central pathology. A decreased sleep latency time with quick onset of REM sleep noted on the polysomnogram is indicative of narcolepsy, which may mimic OSAS. If this is suspected, the multi sleep latency test (MSLT) may help in the diagnosis.

TREATMENT

The treatment of OSAS has been the area of much research in recent years. The interventions are aimed at correcting or altering one or more of the factors contributing to airway closure. This includes attempting to raise the intra-pharyngeal pressure above that at which the pharyngeal walls collapse, decreasing the pressure at which pharyngeal closure occurs or increasing the activity within the pharyngeal musculature in order to maintain the patency of the airway. There are both surgical and non-surgical treatment options aimed at accomplishing these goals.

All overweight patients with OSAS should be encouraged to attempt weight loss. Many studies have reported resolution of obstructive episodes with loss of excess weight. While short-term results suggest good outcomes, long-term results vary. Most patients find it difficult to maintain their losses with dietary measures alone, but for the motivated and dedicated patient, this may cure the disorder. For patients with severe OSAS, weight loss should be viewed as adjunctive therapy as the long-term resolution of the syndrome with weight loss alone is unlikely. Patients should also be instructed to avoid alcohol and other sedating substances as these will only exacerbate the disorder and avoidance may relieve many of their symptoms.

Pharmacotherapy has been suggested as a treatment for sleep apnea. The most widely prescribed agent is Protriptyline (Vivactyl), a tricyclic antidepressant. It functions to decrease the time spent in REM sleep, the period at which pharyngeal muscle tone is at a nadir and the airway is most susceptible to obstruction. Results of therapy are variable but it appears to have some benefit. Many patients find the medication difficult to continue secondary to anticholinergic side effects. Other drugs used in the treatment of sleep apnea include progesterone, acetazolamide and theophylline, all of which function to increase respiratory drive. These agents have some effectiveness in the treatment of central apneas, but have shown little or no benefit in the treatment of OSAS.

Recently, much investigation has been performed in the production of orthodontic devices which act to lift the mandible anteriorly thereby opening the pharyngeal airway at the base of the tongue. Several such appliances have been designed and apparently are somewhat effective in relieving episodes of obstruction. They are often poorly tolerated due to patient discomfort, however. Similar problems have arisen with such interventions as a tongue-retaining splint designed to hold the tongue anteriorly and nasal trumpet placement prior to sleep. While the principles of their mechanisms of action are sound and laboratory trials report their effectiveness, these treatments are not widely applied due to little practicality for most patients.

The most widely used and perhaps the most effective treatment for OSAS is nasal continuous positive airway pressure (CPAP). CPAP requires the application of a mask placed over the nose with a tube connected to a small air compressor that generates a continuous positive pressure within the airway. This positive pressure eliminates the negative pressure within the pharyngeal lumen thereby acting as a pneumatic splint maintaining airway patency. The applied pressure can be adjusted depending upon the particular patient's needs for adequate relief of the obstructive episodes, usually requiring between 7 to 15 cm water. Effectiveness has been reported to be as high as 100%. The main drawback to CPAP is poor patient compliance. The reported compliance rates range from 50 to 80% with failures due to discomfort of the mask, noise from the compressor, nasal complaints including dryness and irritation or just general intolerance.

There are many surgical options for the treatment of OSAS. Tracheostomy has long been recognized as the cure for OSAS by completely bypassing the sites of obstruction. The long-term care required and cosmetic implications associated with the procedure make it a less than desirable choice for most patients. In general, tracheostomy should be reserved for those patients who have failed more conservative treatment modalities, morbidly obese patients with severe OSAS or those with life threatening cardiopulmonary complications. Due to the fact that many of the patients receiving tracheostomy for the treatment of OSAS are morbidly obese, it may be advisable to consider alternative surgical techniques when performing the procedure. These include the removal of adipose tissue from around the tracheostomy site with the creation of skin flaps which may be sutured to the tracheal wall. This technique lessens the risk of granulation tissue formation at the tracheostomy site and allows for easier tube replacement should it become displaced in the immediate post-operative period.

Tonsillectomy and adenoidectomy is the preferred treatment for OSAS in children. This often leads to complete resolution of symptoms and the long term complications. Rarely, morbidly obese children may continue to experience obstructive episodes after tonsillectomy and adenoidectomy and may require more traditional surgical procedures such as UPPP or tracheostomy.

The most widely performed surgical procedure for the treatment of OSAS in adults is the uvulopalatopharyngoplasty (UPPP). The procedure is designed to remove a portion of the excess tissue from the posterior edge of the soft palate thereby relieving obstruction at that level. A tonsillectomy is performed as a part of the procedure. In those patients with severe OSAS and secondary cardiopulmonary disease or arrythmias, tracheostomy may be performed either prior to or at the time of the UPPP. This allows for adequate airway control both pre and post operatively. A post operative sleep study may be performed both with the tracheostomy plugged and unplugged to determine the effectiveness of the procedure. The response of the disease process to UPPP is variable, but is generally reported to be approximately 50%. Significant improvement has been reported as a 50% reduction in the AHI or in the amount of oxyhemoglobin desaturation. Studies have shown that while many patients respond well within the first post-operative year, long term results are not as encouraging. Patients with mild to moderate OSAS seem to have the best outcomes and patient selection may have a significant role in the success of the procedure.

Additional procedures may be performed in conjunction with or in addition to UPPP in an effort to improve outcomes. If significant nasal obstruction is identified on physical examination, correction should be considered. It is unlikely that correction of the nasal obstruction alone will relieve the patient from obstructive episodes, but the patient may achieve significant subjective relief. A small number of patients, most of whom failed UPPP, have undergone laser midline glossectomy in an attempt to remove obstruction at the level of the base of tongue. Experience with this procedure is quite limited and it has not been widely accepted.

Other authors have reported success with surgical procedures which alter the configuration of the facial skeleton and thus the airway. These procedures include techniques for advancement of the mandible in those noted to be significantly retrognathic. Mandibular advancement has been combined with a LeFort I osteotomy and advancement of the maxilla. Infrahyoid myotomy and suspension of the hyoid bone combined with inferior sagittal osteotomy of the mandible for genioglossus advancement has shown promising results. Hyoid expansion in which the hyoid bone is divided into three portions, expanded laterally then secured to an arch bar-type of device and thus expanding the hypopharyngeal airway has been reported as an experimental procedure, but has failed to yield consistent results in patients.

Because of the often tenuous airway and high incidence of cardiopulmonary disease in patients with OSAS, general anesthesia may be particularly difficult. Mask anesthesia and conventional intubation techniques may be unsuccessful, thus the anesthesiology service should be forewarned and preparations made for nasal or fiberoptic intubation should such measures become necessary. In addition, sedatives and paralytic agents should be used with caution without a secure airway. As stated previously, tracheostomy should be considered for peri-operative airway management in those patients with severe OSAS. Steroid therapy both intra- and post-operatively may be effective in reducing swelling and facilitate extubation. Extubation should be performed only when the patient is fully awake, which may require leaving the endotracheal tube in place until the day after the procedure.

Post-operative narcotics and other sedatives are to be used with great caution as patients frequently will experience decreased respiratory drives secondary to the high pO2 and low pCO2 resulting from intubation and mechanical ventilation. Patients with arrythmias or low minimum saturations on polysomnograpphy should receive post-operative cardiac and pulmonary monitoring which may necessitate ICU placement.

Like other procedures in the oropharynx, UPPP has the risks of post-operative bleeding and infection. Antibiotic prophylaxis is routinely given. Post-operative pain may be significant and difficult to control. Aggressive resection of the free margin of the soft palate may result in velopharyngeal incompetence with no clear evidence suggesting increased benefit. The palatal incision should therefore extend no higher on the soft palate than the natural crease formed at the point where the palate contacts Passavant's ridge. Although examination may suggest lymphoid tissue within the nasopharynx, this tissue usually represents redundant mucosa and nasopharyngeal stenosis may complicate an attempted adenoidectomy.

A small percentage of children undergoing adenotonsillectomy for upper airway obstruction will experience postobstructive pulmonary edema. This potenially life-threatening complication is frequently manifested immediately upon intubation. Symptoms include respiratory distress, tachypnea and increased secretions. Treatment is similar to that for other forms of pulmonary edema.

CONCLUSION

Obstructive sleep apnea syndrome is not only a disease that presents with symptomatology that is troubling to the patient and their family, but has severe complications which may be life-threatening. Despite new insight into the causes of the syndrome, treatment modalities remain suboptimal. Non-surgical treatments are limited by poor patient compliance, while surgical procedures have variable outcomes. Proper patient selection and long-term follow up may increase the effectiveness of the therapies and decrease the morbidity and mortality associated with the syndrome.

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