Sleep apnea can be caused by a person’s physical structure or medical conditions. These include obesity, large tonsils, disorders, neuromuscular disorders, heart or kidney failure, certain syndromes, and premature birth.
Obesity is a common cause of sleep apnea in adults. People with this condition have increased fat deposits in their necks that can block the upper airway.
Large tonsils may contribute to sleep apnea, because they narrow the upper airway.
The endocrine system produces that can affect sleep-related breathing. The following are examples of endocrine disorders associated with sleep apnea:
- Hypothyroidism: People with this condition have low levels of . This affects the part of the brain that controls breathing, as well as the nerves and muscles used to breathe. People with hypothyroidism can also be diagnosed with obesity, which can cause sleep apnea.
- Acromegaly: People with this condition have high levels of growth hormone. This condition is associated with changes in the facial bones, swelling of the throat, and an increased size of the tongue. These changes can obstruct the upper airway and lead to sleep apnea.
- Polycystic ovary syndrome (PCOS): Sleep apnea is also seen in women with PCOS, an endocrine condition that causes large ovaries and prevents proper ovulation. PCOS is also associated with overweight and obesity, which can cause sleep apnea.
Heart or kidney failure
Sleep apnea is commonly found in people who have advanced heart or kidney failure. These patients may have fluid build-up in their neck, which can obstruct the upper airway and cause sleep apnea.
Genetic syndromes that affect the structure of the face or skull, particularly syndromes that cause smaller facial bones or cause the tongue to sit farther back in the mouth, may cause sleep apnea. These genetic syndromes include cleft lip and cleft palate, Down syndrome and congenital central hypoventilation syndrome.
Babies born before 37 weeks of pregnancy have a higher risk for breathing problems during sleep. In most cases, the risk decreases as the brain matures.
There are many risk factors for sleep apnea. Some risk factors, such as unhealthy lifestyle habits and environments, can be changed. Other risk factors, such as age, family history and genetics, race and ethnicity, and sex, cannot be changed. Heathy lifestyle changes can decrease your risk for developing sleep apnea.
Sleep apnea can occur at any age. The risk for sleep apnea increases as you get older. In younger adults, sleep apnea is more common in men than in women, but the difference decreases later in life. Normal age-related changes in how the brain controls breathing during sleep partially explain the increased risk as you get older. Another possible reason is that as we age, more fatty tissue builds up in the neck and the tongue.
Unhealthy lifestyle habits
Drinking alcohol, smoking, and overweight or obesity can increase your risk for sleep apnea.
- Alcohol can increase relaxation of the muscles in the mouth and throat, closing the upper airway. It can also affect how the brain controls sleep or the muscles involved in breathing.
- Smoking can cause in the upper airway, affecting breathing, or it can affect how the brain controls sleep or the muscles involved in breathing.
- Unhealthy eating patterns and lack of physical activity can lead to overweight and obesity, which can result in sleep apnea.
Family history and genetics
Researchers have identified family history as a risk factor for sleep apnea, but maintaining a healthy lifestyle can decrease this risk. Studies in twins have shown that sleep apnea can be . Some of the related to sleep apnea are associated with the structural development of the face and skull and with how the brain controls sleep and breathing during sleep. Some genes are also associated with obesity and inflammation.
Race or ethnicity
In the United States, sleep apnea is more common among blacks, Hispanics, and Native Americans than among whites.
Screening and Prevention
Screening for sleep apnea
To screen for sleep apnea or other sleep disorders, your doctor may ask you about common signs and symptoms of this condition, such as how sleepy you feel during the day or when driving, and whether you or your partner has noticed that you snore, stop breathing, or gasp during your sleep. Your doctor may ask questions to assess your risk for developing this condition and take your physical measurements. Your doctor will also want to see whether you have any complications of undiagnosed sleep apnea, such as high blood pressure that is difficult to control. If the screening suggests a sleep breathing disorder, you may get a referral to a sleep specialist to help confirm a diagnosis.
Healthy lifestyle changes to prevent sleep apnea
If you are concerned about having risk factors for developing sleep apnea, ask your doctor to recommend healthy lifestyle changes, including eating a heart-healthy diet, aiming for a healthy weight, quitting smoking, and limiting alcohol intake. Your doctor may recommend that you sleep on your side and adopt healthy sleep habits such as getting the recommended amount of sleep.
- Diagnosis will discuss tests and procedures that your doctor may use to diagnose sleep apnea and rule out other conditions or medicines that may be causing symptoms of sleep apnea.
- Living With will explain what your doctor may recommend to prevent your sleep apnea from recurring, getting worse, or causing complications.
- Research for Your Health will discuss how we are using current research and advancing research to prevent sleep apnea.
- Participate in NHLBI Clinical Trials will explain our ongoing clinical trials that are investigating prevention strategies for sleep apnea.
Signs, Symptoms, and Complications
Common sleep apnea signs and symptoms are snoring or gasping during sleep; reduced or absent breathing, called apnea events; and sleepiness. Undiagnosed or untreated sleep apnea prevents restful sleep and can cause complications that may affect many parts of your body.
Signs and symptoms
Common of sleep apnea:
- Reduced or absent breathing, known as apnea events
- Frequent loud snoring
- Gasping for air during sleep
Common of sleep apnea:
- Excessive daytime sleepiness and fatigue
- Decreases in attention, vigilance, concentration, motor skills, and verbal and visuospatial memory
- Dry mouth or headaches when waking
- Sexual dysfunction or decreased libido
- Waking up often during the night to urinate
Did you know that sleep apnea symptoms may be different for women and children compared with men?
Sleep apnea may increase your risk of the following disorders:
- Atrial fibrillation
- Cancers, such as pancreatic, renal, and skin cancers
- Chronic kidney disease
- Cognitive and behavioral disorders, such as decreases in attention, vigilance, concentration, motor skills, and verbal and visuospatial memory, as well as dementia in older adults. In children, sleep apnea has been associated with learning disabilities.
- Diseases of the heart and blood vessels, such as atherosclerosis, heart attacks, heart failure, difficult-to-control high blood pressure, and stroke
- Eye disorders, such as glaucoma, dry eye, or keratoconus
- Metabolic disorders, including glucose intolerance and type 2 diabetes
- Pregnancy complications, including gestational diabetes and gestational high blood pressure, as well as having a baby with low birth weight
Did you know that sleep apnea can cause inflammation and lead to complications?
When blood oxygen levels drop due to obstructive sleep apnea, your body and brain trigger the “fight or flight” response. This increases your blood pressure and heart rate and wakes you from sleep so that your upper airway can open. These cycles of decreased and increased blood oxygen levels can cause inflammation that may contribute to atherosclerosis, the buildup of in blood vessels, which can increase the risk of heart attack or stroke. Chronic inflammation can also damage the pancreas and lead to type 2 diabetes.
Your doctor may diagnose sleep apnea based on your medical history, a physical exam, and results from a sleep study. Before diagnosing you with sleep apnea, your doctor will rule out other medical reasons or conditions that may be causing your signs and symptoms.
To help diagnose sleep apnea, your doctor may consider the following:
- Information that you provide, such as signs and symptoms that you are experiencing
- Whether you have a family history of sleep apnea or another sleep disorder
- Whether you have risk factors for sleep apnea
- Whether you have complications of undiagnosed or untreated sleep apnea, such as atrial fibrillation, type 2 diabetes, or hard-to-control high blood pressure
During the physical exam, your doctor will look for signs of other conditions that can increase your risk for sleep apnea, such as obesity, large tonsils, narrowing of the upper airway, or a large neck circumference. A neck circumference greater than 17 inches for men or 16 inches for women is considered large. Your doctor may also look at your jaw size and structure, the size of your tongue, and your tongue’s position in your mouth. Your doctor will check your lungs, heart, and neurological systems to see whether you have any common complications of sleep apnea.
To diagnose sleep apnea or another sleep disorder, your doctor may refer you to a sleep specialist or a center for a sleep study. Sleep studies can be done in a special center or at home. Studies at a sleep center can:
- Detect apnea events, which are times when your breathing stops or slows during sleep
- Detect low or high levels of activity in muscles that control breathing
- Monitor blood oxygen levels during sleep
- Monitor brain and heart activity during sleep
Your doctor may be able to diagnose mild, moderate, or severe sleep apnea based on the number of sleep apnea events you have in an hour during the sleep study.
- Mild: Five to 14 apnea events in an hour
- Moderate: 15 to 29 apnea events in an hour
- Severe: 30 or more apnea events in an hour
Visit Sleep Studies for more information.
Did you know that sleep studies can help determine which type of sleep apnea you have?
Sleep studies can monitor the movement of your muscles and help determine breathing patterns and whether you have obstructive or central sleep apnea. Sleep studies of patients with obstructive sleep apnea often show an increase in breathing muscle activity when muscles try to open an obstructed upper airway. In contrast, sleep studies of patients with central sleep apnea tend to show decreased activity in chest muscles, which can lead to periods of slowed or no breathing.
Ruling out other medical reasons or conditions
Your doctor may order the following tests to help rule out other medical conditions that can cause sleep apnea:
- Blood tests to check the levels of certain hormones and to rule out endocrine disorders that could be contributing to sleep apnea. Thyroid hormone can rule out hypothyroidism. Growth hormone tests can rule out acromegaly. Total testosterone and dehydroepiandrosterone sulphate (DHEAS) tests can help rule out polycystic ovary syndrome (PCOS).
- Pelvic ultrasound to examine the ovaries and detect cysts. This can rule out PCOS.
Your doctor will also want to know whether you are using medicines, such as opioids, that could be affecting your sleep or causing breathing symptoms of sleep apnea. Your doctor may want to know whether you have traveled recently to altitudes greater than 6,000 feet, because these low-oxygen environments can cause symptoms of sleep apnea for a few weeks after traveling.
- Return to Risk Factors to review family history, lifestyle, or other environmental factors that increase your risk of developing sleep apnea.
- Return to Signs, Symptoms, and Complications to review common symptoms of sleep apnea.
- Return to Screening and Prevention to review how to screen for and prevent sleep apnea.
If you are diagnosed with sleep apnea, your doctor may make recommendations to help you maintain an open airway during sleep. These could include healthy lifestyle changes or a breathing device such as a positive airway pressure (PAP) machine, mouthpiece, or implant. Talk to your doctor. Depending on the type and severity of your sleep apnea and your needs and preferences, other treatments may be possible.
Healthy lifestyle changes
To help control or treat your sleep apnea, your doctor may recommend that you adopt lifelong healthy lifestyle changes.
- Make heart-healthy eating choices. This also includes limiting your alcohol intake, especially before bedtime.
- Get regular physical activity.
- Aim for a healthy weight. Research has shown that losing weight can reduce sleep apnea in people who were also diagnosed with obesity.
- Develop healthy sleeping habits. Your doctor may recommend general healthy sleep habits, which include getting the recommended amount of sleep based on your age.
- Quit smoking. Visit Smoking and Your Heart and the National Heart, Lung, and Blood Institute’s Your Guide to a Healthy Heart [PDF 2.9MB]. Although these resources focus on heart health, they include basic information about how to quit smoking. For free help and support to quit smoking, call the National Cancer Institute’s Smoking Quitline at 1-877-44U-QUIT (1-877-448-7848).
A breathing device, such as a CPAP machine, is the most commonly recommended treatment for patients with sleep apnea. If your doctor prescribes a CPAP or other breathing device, be sure to continue your doctor-recommended healthy lifestyle changes. Read Living With to learn more about properly caring for your breathing device.
Mouthpieces, or oral appliances, are typically custom-fit devices that you wear while you sleep. There are two types of mouthpieces that work differently to open the upper airway. Some hybrid mouthpieces have features of both types.
- Mandibular repositioning mouthpieces are devices that cover the upper and lower teeth and hold the jaw in a position that prevents it from blocking the upper airway.
- Tongue retaining devices are mouthpieces that hold the tongue in a forward position to prevent it from blocking the upper airway.
Your doctor may prescribe a mouthpiece if you have mild sleep apnea or if your apnea occurs only when you are lying on your back. To get your mouthpiece, your doctor may recommend that you visit a dentist or an orthodontist, a type of dentist who specializes in correcting teeth or jaw problems. These specialists will ensure that the oral appliance is custom fit to your mouth and jaw.
Implants can benefit some people with sleep apnea. Some devices treat both obstructive and central sleep apnea. You must have surgery to place an implant in your body. The Food and Drug Administration has approved one implant as a treatment for sleep apnea. The device senses breathing patterns and delivers mild stimulation to certain muscles that open the airways during sleep. More research is needed to determine how effective the implant is in treating central sleep apnea.
A nerve stimulator can also treat sleep apnea. This treatment also involves surgery. A surgeon will insert a stimulator for the hypoglossal nerve, which controls tongue movement. Increasing stimulation of this nerve helps position the tongue to keep the upper airway open.
Therapy for mouth and facial muscles
Children and adults with sleep apnea may benefit from therapy for mouth and facial muscles, known as orofacial therapy. This therapy helps improve tongue positioning and strengthen muscles that control the lips, tongue, soft palate, lateral pharyngeal wall, and face.
You may need surgery if you have severe obstructive sleep apnea that does not respond to breathing devices such as a CPAP machine, or that is caused by visible obstruction to the upper airway, perhaps due to large tonsils. Possible surgical procedures include:
- Tonsillectomy: a surgery to remove the tonsils, which are organs at the back of your throat
- Maxillary or jaw advancement: a surgery to move the upper jaw (maxilla) and lower jaw (mandible) forward, to enlarge the upper airway
- Tracheostomy: a surgery to make a hole through the front of your neck into your trachea, or windpipe. A breathing tube, called a trach tube, is placed through the hole and directly into your windpipe to help you breathe.
If surgery is considered as a possible treatment, talk to your doctor about the different types of surgical procedures, the risks and benefits of the procedures, potential discomfort, and the recovery time you will need after surgery.
- Living With will explain what your doctor may recommend, including lifelong lifestyle changes and medical care to prevent your condition from recurring, getting worse, or causing complications.
- Research for Your Health will discuss how we are using current research and advancing research to treat people with sleep apnea.
- Participate in NHLBI Clinical Trials will discuss our ongoing clinical studies that are investigating treatments for sleep apnea.
If you have been diagnosed with sleep apnea, it is important that you adopt and maintain healthy lifestyle habits and use your prescribed treatment. Read more about how to use and care for your breathing device or mouthpiece, how your doctor may monitor whether your treatment is working, and when you may need a repeat sleep study. Learn other tips to keep you safe if you have sleep apnea.
Using and caring for your breathing device or mouthpiece
It is important that you properly use and care for your prescribed breathing device or mouthpiece. If your doctor prescribed a breathing device or CPAP machine:
- Be patient with your breathing device or CPAP machine. It may take time to adjust to breathing with the help of a CPAP machine.
- Use your breathing device or CPAP machine for all sleep, including naps. To benefit fully from your treatment, you should wear your device whenever and wherever you sleep. If you are traveling, be sure to bring your breathing device with you. Call your doctor or sleep specialist right away if your device stops working correctly.
- Talk to your doctor or supplier if you experience discomfort or have difficulty using your prescribed breathing device. Let the team or supplier know if you are having irritation from the mask, if your mask is not staying on or fitting well, if it leaks air, if you are having difficulty falling or staying asleep, if you wake with dry mouth, or if you have a stuffy or runny nose. Your doctor can explore options to improve the treatment, such as trying different masks or nasal pillows, adjusting the machine’s pressure timing and settings, or trying a different breathing device that has a humidifier chamber or provides bi-level or auto-adjusting pressure settings. Cleaning the mask and washing your face before putting your mask on can help make a better seal between the mask and your skin.
- Properly care for your breathing device or CPAP machine. Know how to set up and properly clean all parts of your machine. Be sure to refill prescriptions on time for all of the device’s replaceable parts, including the tubes, masks, and air filters.
- Properly care for your mouthpiece. If you were prescribed a mouthpiece, ask your dentist how to properly care for it. If it does not fit right or your signs and symptoms do not improve, let your dentist know so that he or she can adjust the device. It is common to feel some discomfort after a device is adjusted until your mouth and facial muscles get used to the new fit.
Monitor your condition
You should visit your doctor to monitor your response to treatment and see whether you have any complications that, if left untreated, can be life-threatening. Your doctor may do any of the following to monitor your condition.
- If your doctor prescribed a breathing device, your doctor and possibly your insurance company will want to check the data card from the machine. The data card shows how often you use the breathing device and whether the device and its pressure settings are helping to reduce or eliminate apnea events while you sleep. Your doctor may also check to see whether you still experience excessive sleepiness during the day, how you feel about your quality of life, whether you are still snoring, or whether have experienced weight loss or changes in your lifestyle.
- If you were prescribed a mouthpiece, you should follow up with your dental specialist after six months and then at least every year. This is to see whether the mouthpiece is working correctly, whether it needs adjustment, and whether a replacement device is needed.
Repeat sleep studies
Sometimes, repeat sleep studies are necessary. Your doctor may have you repeat a sleep study to monitor your response to the treatment, especially if your sleep symptoms continue, if you are using a mouthpiece, if your weight changes significantly, or if your employer requires these tests.
Learn the warning signs of some CPAP side effects
Side effects of CPAP treatment may include congestion, runny nose, dry mouth, dry eyes, or nosebleeds. If you experience stomach discomfort or bloating, you should stop using your CPAP machine and contact your doctor.
Learn about other precautions to help you stay safe
Sleep apnea can increase your risks of complications if you are having surgery, and it can affect your ability to drive.
- Before surgery. If you are having any type of surgery that requires medicine to put you to sleep or for pain management, let your surgeon and doctors know that you have sleep apnea. They might have to take extra steps to make sure that your upper airway stays open during the surgery and when selecting your pain medicines.
- Driving precautions. Undiagnosed and untreated sleep apnea can decrease learning capabilities, slow down decision making, and decrease attention span, which can result in drowsy driving.
Improving health with current research
Learn about the following ways the NHLBI continues to translate current research into improved health for people with sleep apnea.
- Sleep Disorders Research Advisory Board (SDRAB). The NHLBI has administered this specialty program advisory panel since 1993. Board members, including medical professionals, federal partners, and members of the public, meet regularly to provide feedback to the NIH on sleep-related research needs and to discuss how to move sleep research forward. Visit the Sleep Disorders Research Advisory Board for more information.
- National Sleep Research Resource (NSRR). This resource was established by the NHLBI to provide biomedical researchers a large, well-characterized data collection from NIH-funded sleep research studies. These data can be used in new research studies to advance sleep research. Visit the National Sleep Research Resource for more information.
- Identification of genes that increase susceptibility to obstructive sleep apnea. The NHLBI Trans-Omics for Precision Medicine (TOPMed) program and its Whole-Genome Sequencing (WGS) project is using WGS data to identify genetic variations that may increase the risk of obstructive sleep apnea. Visit the Cleveland Family Study-WGS Collaboration (CFS Sleep Apnea) for more information.
Learn about some of our pioneering research contributions that have improved clinical care.
- Association between sleep apnea and increased risk of death from diseases of the heart and blood vessels. The NHLBI-supported Wisconsin Sleep Study, which followed groups of Wisconsin state employees for up to 18 years, found that severe sleep apnea increased the risk of dying from diseases of the heart and the blood vessels by five times among study participants who had never used a CPAP machine. The study also found that severe sleep apnea triples the risk of death from all causes, even among participants treated for sleep apnea.
- Association between sleep apnea and diabetes. An NHLBI partnership with the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) discovered that sleep apnea affects more than 80 percent of obese individuals with type 2 diabetes. The study also found that weight loss reduced sleep apnea better than a diabetes education program. These findings have led to additional study partnerships to determine whether sleep apnea affects how well medicine can control the blood sugar of people with diabetes.
- Genetic bases of sleep apnea. The Candidate-gene Association Resource (CARe) study supported by the NHLBI discovered specific areas of genes (loci) that are more common in sleep apnea patients. Understanding the genetics involved in obstructive sleep apnea may allow the development of new treatments for this disorder.
- Partnering on sleep apnea and pregnancy outcomes research. The NHLBI partnered with the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) in the Nulliparous Pregnancy Outcomes Study Monitoring Mothers to Be (nuMoM2B) study, which revealed that sleep deficiency and mild sleep apnea in pregnant women increases the risk of pregnancy complications such as preeclampsia and diabetes. The NHLBI and NICHD are now studying whether the treatment of sleep apnea during pregnancy reduces these risks.
- Association between sleep disorders and pain. The NHLBI participated in the 2014 Trans-NIH Sleep/Pain Workshop, in which sleep and pain researchers reviewed evidence and proposed new research topics to increase understanding of the role of sleep disorders, including sleep apnea, in chronic pain. Visit Trans-NIH Sleep/Pain Workshop Summary: Contribution of Sleep Disturbances to Chronic Pain for more information.
Advancing research for improved health
In support of our mission, we are committed to advancing sleep apnea research in part through the following ways:
- We perform research. The NHLBI Division of Intramural Research and its Systems Biology Center are studying how genes and the environment influence sleep.
- We fund research. The research we fund today will help improve our future health. Our Division of Lung Diseases is home to the National Center on Sleep Disorders Research (NCSDR), which supports research on sleep and the circadian biology of sleep disorders, including how the body regulates breathing during sleep, how sleep deficiencies affect the whole body, and what biomarkers can help assess sleep health. Other NHLBI Divisions support sleep research, including why sleep deficiency is a risk factor for obesity, stroke, and some cardiovascular diseases, and how sleep and biology affect blood clotting, the immune system, and blood cell production. Search the NIH RePORTER to learn about research that the NHLBI is funding on sleep apnea.
- We stimulate high-impact research. Through our Trans-Omics for Precision Medicine (TOPMed) program, researchers will use data from studies focused on heart, lung, blood, and sleep disorders to better predict, prevent, diagnose, and treat sleep disorders based on a patient’s unique genes, environment, and molecular signatures. The NHLBI Strategic Vision highlights ways we may support research over the next decade, including new efforts for sleep apnea.
Learn about exciting research areas that the NHLBI is exploring about sleep apnea.
- Effects of sleep apnea in type 2 diabetes. The NHLBI is supporting studies to understand the association between obstructive sleep apnea severity, control of and changes in blood sugar, and the responses to CPAP therapy in patients who have type 2 diabetes.
- Hormonal changes in sleep deprivation. We know that sleep deprivation decreases the response of the body to , but it is not clear how. Nevertheless, it looks like and testosterone play an important role. The NHLBI is supporting research to help understand this mechanism.
- Monitors for mouthpieces. The NHLBI is supporting the development and testing of new technologies to track patient compliance and the effectiveness of mouthpieces in the management of sleep apnea.
- New diagnostic test for sleep apnea. The NHLBI is interested in finding potential markers in blood and urine, including inflammatory substances, as well as genetic changes in patients with sleep apnea and with or without diseases of the heart and the blood vessels.
- Patient position after surgery and sleep tests. We know that patients with sleep apnea can have more complications after surgery. NIH is supporting a study to evaluate whether having the patient in semi-upright position, instead of the traditional prone position (on the back), can decrease complications and hospital stay.
- Screening tool for sleep apnea. Current screening tools for sleep apnea are not ideal, and sleep studies are expensive, which limits their use for screening. The NHLBI is supporting studies to test the effectiveness of possible screening methods for sleep apnea, such as the STOP-BANG Screening Questionnaire.
- Participate in NHLBI Clinical Trials will discuss how to participate in our clinical trials for sleep apnea.
We lead or sponsor many studies relevant to sleep apnea. See whether you or someone you know is eligible to participate in our .
Do you have an adolescent or young adult with sleep apnea and Down syndrome?
Are you an adult with sleep apnea who wants to help understand this disease by using an oral appliance?
Are you an adult with sleep apnea who would like to try a new treatment with facial exercises?
Are you an adult with sleep apnea and type 2 diabetes?
Are you an adult who recently was diagnosed with sleep apnea?
Are you a Minnesota resident with hypertrophic cardiomyopathy?
Do you have a child with sleep apnea who is interested in a new treatment with a nasal spray?
Are you an adult with sleep apnea who finds it hard to use your CPAP machine?
After reading our Sleep Apnea Health Topic, you may be interested in additional information found in the following resources.
Related Health Topics
- Aim for a Healthy Weight
- Sleep apnea: NHLBI sheds light on an underdiagnosed disorder
- Sleep Science and Sleep Disorders
- The National Center on Sleep Disorders Research (NCSDR)
- Always Tired? You May Have Sleep Apnea (U.S. Food and Drug Administration)
- Driving When You Have Sleep Apnea (Federal Motor Carrier Safety Administration)
- Is my test, item, or service covered? (Centers for Medicare & Medicaid Services)
- National Healthy Sleep Awareness Project (Centers for Disease Control and Prevention)
- Obstructive Sleep Apnea (OSA): Overview for the Aerospace Community [PDF, 1.5M] (Federal Aviation Administration)
- Sleep Apnea Information Page (National Institute of Neurological Disorders and Stroke)
- Sleep Apnea (U.S. National Library of Medicine)