Sleep Apnea – CPAP / Questions, Answers, and Help Videos

What is CPAP?

The acronym CPAP refers to continuous positive airway pressure. In practical terms, CPAP is a device that maintains air pressure in your throat to keep a vacuum from forming that pulls your tongue and palate down so that they block the flow of air.

CPAP Machine

The CPAP machine blows air into your nose through tubing to a mask that fits over your face. The mask is necessary to keep air pressure generated by the machine from dissipating into your bedroom. There is a valve on the side of the mask that opens to let air in the unlikely event that the power goes off during the night.

The faster the rate at which air flows, the less pressure it exerts. The flow of air from the machine is fastest at your nostrils, but it slows down as it enters the back of your throat. The air flow does not cause your nostrils to flare, but it causes your windpipe to open wider and wider as the air current slows down. The flow of air acts as a "pneumatic splint" that supports the muscles surrounding the throat in much the same way as a splint or cast supports a broken bone.

There is a wide variety of prescription headgear and headgear straps for CPAP, with products for every need.

• A full-face mask product deals with the problem of sensitive skin on the face, since it forms a seal around the face and does not rely on silicone cushions on the face. It does not allow for much freedom of movement.

• A hybrid mask combines both nasal pillows and head gear to hold the mask in place.

• A nasal pillow nasal mask fits over just the nose, not the mouth. The nasal pillow mask forms a cushion on the face, and a vent in the center of the mask allows for the escape of carbon dioxide. There are models of nasal pillows that can be worn underneath glasses, for people who have daytime apnea.

• A nasal prong mask fits over the nostrils but not directly on the face for nighttime ventilation. If it has a swivel, it allows the user to sleep in any position.

• A total-face CPAP mask fits over both face and mouth, and is usually attached by straps to the facial mask both across the forehead and across the chin. It prevents the escape of air from the mouth, and by helping to keep the mouth shut during the night, it prevents skin irritation, dry mouth, and sore throats.

• An oral mask fits over the mouth but not the nose. It should only be used when there is a humidifier with the CPAP equipment. The oral mask allows considerable freedom of movement and prevents leaking that lowers air pressure for people who tend to be mouth breathers.

Which CPAP masks are best? The answer is always "it depends." The wide variety of masks makes it possible for nearly everyone to find a fit for comfort.

CPAP Prescription

The air flow that is needed to keep the tongue and palate from sliding down and back during the night varies from person to person depending on a variety of factors. CPAP is not "one setting fits all." Determining the right airflow, a process called titration, has to be done for your individual needs and it has to be done while you are asleep. You can't do this for yourself, although you can use the settings the doctor has determined for you on a different machine.

What is titration?

Titration is the process of finding the right amount of pressure to stop sleep apnea and hypopnea so your blood oxygen levels will stay normal all through the night. Usually a technician does this during the second half of your overnight stay. Sometimes titration is done during a second overnight sleep study. The right setting for your CPAP machine is the one that prevents allows you to sleep in any position, even on your stomach, without snoring, waking up, or falling oxygen levels.

CPAP Air Pressure

The process of titration comes up with a number that corresponds to the amount of air needed to support a column of water a certain number of centimeters high. That number is almost always between 5 and 20 centimeters. It is just a convenient way of measuring air pressure. As long as you are sleeping at the same altitude all the time, you should always use this setting. Setting your machine too low won't prevent sleep apnea, and setting your machine too high may cause air leaks around the face mask, waking you up, or even blow the mask off your face, leaving you vulnerable to sleep apnea.

Auto CPAP

An auto-PAP machine is a CPAP machine that can make automatic adjustments for changes in air pressure in your sleeping area and also compensate for changes in your sleep position.

CPAP Compliance

Compliance refers to actual use of the CPAP machine. Most modern CPAP machines keep track of both "machine on" hours and "mask on" hours, and can prepare a report for your doctor.

Minumum Benefits of CPAP

Clinical studies show that the minimum benefits of CPAP kick in when the machine is used at least 4 hours per night at least 5 nights per week. This is the minimum amount of machine use that makes a difference in one of the measurements of the severity of sleep deprivation, the Epworth Sleep Sleepiness (ESS) scale. If you aren't using CPAP every night for at least 5 or 6 hours per night, you need to make adjustments. You can take care of most throat and nasal problems with masks, hoses, and humidifiers yourself. Other issues may have to be worked out with your doctor.

Here is a brief glossary of CPAP acronyms.

• AHI, apnea-hypopnea index, number of incidents of apnea (breathing cessation) or hypopnea (reduced breathing) per hour. Each apnea incident must last at least 10 seconds or more. An AHI of less than 15 is considered mild, more than 15 up to 30 is moderate, and more than 30 is severe. An AHI of less than 5 is not likely to be treated with CPAP.

• AASM, American Academy of Sleep Medicine, grants accreditation to sleep centers in the United States.

• BANG and STOP. Acronyms for quick diagnosis of likely obstructive sleep apnea. BANG: BMI greater than 35, age greater than 50 years, neck circumference greater than 430 mm/17 inches, gender male. STOP: snore loud enough to be heard through closed door, tired almost every day, observed not breathing during sleep, history of high blood pressure. Two more symptoms from each group indicates 94% likelihood of obstructive sleep apnea.

• BiPAP, bilevel positive airway pressure. Allows for different pressures during inhalation and exhalation. Used for treatment of sleep apnea in people who experience bloating or ear problems.

• BMI, body mass index (measure of weight relative to height).

• BP, blood pressure.

• CHF, congestive heart failure, a potential long-term complication of sleep apnea.

• CPAP, continuous positive airway pressure.

• CSA, central sleep apnea.

• EDS, excessive daytime sleepiness.

• EEG, electroencephalographic, referring to brain waves. There are EEG changes during sleep apnea.

• ESS, Epworth Sleepiness Scale.

• HSD, heavy snorer's disease, referring to severe obstructive sleep apnea.

• MLST, Multiple Sleep Latency Test.

• MWT, Maintenance of Wakefulness Test.

• OSA, obstructive sleep apnea.

• OSAH, obstructive sleep apnea-hypopnea (a condition in which the airway is only partially blocked causing less severe deprivation of oxygen during some sleep events).

• PD, patient directed.

• Pcrit, pharyngeal critical pressure, level of air pressure at which the throat collapses and breathing stops.

• PFT, pulmonary function test (measures lung function independent of apnea).

• PSG, polysomnography.

• RDI, respiratory disturbance index, measurement of number of apnea incidents, hypopnea incidents, and respiratory effort-related arousals (caused by snores and snorts) per hour. The RDI is always greater than or equal to the AHI.

• RERA, respiratory effort-related arousal, waking up because of difficulty taking a breath.

• SDB, sleep-disordered breathing.

• SRBD, sleep-related breathing disorder, may include conditions ranging from sleepiness and snoring to sleep apnea.

• UARS, upper airway resistance syndrome, snoring that causes sleep loss without interruption of oxygen supply to the bloodstream.

More often that not the problem is that people stop using the machine for a number of reasons that are easy to correct. There is a great deal more information on CPAP maintenance on this site. However, if you are using your machine as directed, the problem may be:

• CPAP pressure is too low to completely resolve sleep apnea. It is the pressure against an exhalation (which lowers carbon dioxide levels and prevents apnea) that is most often the problem. If you have a BiPAP machine, only the exhalation pressure might need to be adjusted. But you should consult your physician to do this.

• If you didn't drink the night you had your polysomnography test but you usually have a nightcap, your machine may be set too low. Again, your doctor should be involved in making this change of setting.

• Men who start taking Viagra (sildenafil) often have increased frequency of apnea.

• Weight gain increases frequency of apnea.

• If you have undiagnosed narcolepsy, you may also experience "complex" sleep apnea that has to be diagnosed by a physician.

Traveling With CPAP

Unless you have an auto-PAP unit yes. Your CPAP unit will come with instructions in how to do this. If your machine does not have instructions for operation at high altitude, then turn the setting up and then check your readout the next morning to find out what the 95% pressure level should be.

CPAP Machine Troubles

More often than not the problem is that people stop using the machine for a number of reasons that are easy to correct. There is a great deal more information on CPAP maintenance on this site. However, if you are using your machine as directed, the problem may be:

• CPAP pressure is too low to completely resolve sleep apnea. It is the pressure against an exhalation (which lowers carbon dioxide levels and prevents apnea) that is most often the problem. If you have a BiPAP machine, only the exhalation pressure might need to be adjusted. But you should consult your physician to do this.
• If you didn't drink the night you had your polysomnography test but you usually have a nightcap, your machine may be set too low. Again, your doctor should be involved in making this change of setting.
• Men who start taking Viagra (sildenafil) often have increased frequency of apnea.
• Weight gain increases frequency of apnea.
• If you have undiagnosed narcolepsy, you may also experience "complex" sleep apnea that has to be diagnosed by a physician.

BiPAP is a breathing therapy also known as bilevel positive airway pressure. The machine provides higher pressure for breathing in and lower pressure for breathing out.

If your doctor has put you on BiPAP, you need to use it every time you go to sleep, even when you take naps

of the time BiPAP is not covered by Medicaid. Medicare requires extensive documentation of your apnea before it will pay for the machine. Your doctor has to document that your inability to sleep at night causes excessive fatigue, morning headaches, difficulty breathing, or cognitive issues, and the doctor also has to run tests showing that you have:

• A health condition interfering with the normal function of the muscles surrounding the rib cage, such as Lou Gerig's disease or a nerve injury,
• Severe chronic obstructive pulmonary disease, such as chronic asthma or emphysema,
• Central sleep apnea, or
• Obstructive sleep apnea.

Medicare requires sleep apnea to be documented by an overnight sleep study. Medicare also requires followup visits with the doctor in the first 31 days and again before the first 90 days have passed to ensure that your BiPAP or CPAP device is properly titrated (set at the right air pressure) and that you are using it properly. Medicare will also need a download showing that you have used the device 70% of the time during the first 30 days. Most insurance companies have similar guidelines for reimbursing the device.

No, your doctor has to determine the right titration of the air flow to support breathing for you. You should never "borrow" someone else's BiPAP or CPAP machine. Even if someone were to make a gift of a used BiPAP or CPAP machine, it would need be cleaned, you would need your own mask and hoses, and your doctor would have to determine the settings that work best for you.

No, BiPAP works with almost every mask type. However, it is very important that the mask does not leak, since the machine would interpret the lower air pressure caused by the leak as a central sleep apnea event. It's best to use a mask that has been prescribed by a physician to get a good fit.

Make sure the machine is running before you put on the mask. The tighter the straps, the more likely the mask is to leak. BiPAP will not work well when the mask leaks.

You may need to add a humidifier to your machine. If you are already using a humidifier, then a saline mouth or nose rinse may be what you need. Don't use any product that contains alcohol, since the amount of alcohol in most personal care products is high enough to dry out the mouth and mucus membranes but too low to kill germs.

Your BiPAP settings were determined during your sleep study. They may feel high while you are awake but they are needed to help you breathe while you are asleep. Give yourself at least the first month to get used to the feel of BiPAP, then if you still have issues with the way the treatment feels, see you physician.

Sometimes sleep clinics can arrange a 30day athome trial out of a BiPAP machine for people who have to buy their own equipment and are concerned about the price of the machine.

In the United States, companies that provide breathing equipment that is reimbursed by Medicare are not allowed to make solicitation calls to current or potential customers. They are allowed to return calls and to contact you with urgent information about your machine.

Maintaining a BiPAP machine is similar to maintaining a CPAP machine. You should clean the bues and masks every morning. You can use a solution of 10 parts of water with 1 part of vinegar, or you can occasionally use a mild antibacterial soap. Don't use antibacterial soap every day. Some antibacterial soaps kill all but the most resistant strains of bacteria, which can then multiply in your equipment unchecked by competition.

You will also need to change filters once a month. Dust accumulates on top of the machine as it sits next to your bed. If the noise of the machine interferes with sleep, you will need ear plugs. Ear plugs with a porous surface are less irritating to the ears. If you use a humidifier, it needs to be set on your nightstand at a lower level than the BiPAP machine itself.

One way of overcoming an aversion to wearing a face mask while you are asleep is taking an hour or so every evening to practice wearing it while you are awake. Try wearing your face mask (with the machine turned on, of course) while sitting up reading in bed. Then take off the mask and sleep as usual. After a few nights, try wearing the mask to sleep. It may take a few weeks to get used to the mask. Slowly but surely is the best way to adjust to BiPAP.

You probably will. Your doctor will be able to advise you how to connect the machines. Be sure to ask if you need to use a pulsOX meter (finger meter for oxygen levels) to make sure the connections are made properly.

The SV in AutoSV refers to "servo ventilation." When the BiPAP machine is equipped with Automatic Servo Ventilation, a timer ensures that breathing continues by forcing another breath with high pressure air within four minutes of the last exhalation. At the right settings, this prevents obstructions and maintains breathing even when the brain forgets to tell the body to breathe.

A BiPAP machine with Auto SV will automatically deliver higher-pressure air to maintain breathing when breaths drop below a certain level.

Auto SV is keyed to the length of time between respirations. It keeps you breathing even if your brain "forgets" to send a message to your rib cage for you to breathe. The amount of pressure is set by the doctor. This prevents central sleep apnea. Auto BiPAP is designed to change the amount of pressure in the hose to prevent your tongue from slipping back into your throat or your windpipe from collapsing. It prevents obstructive sleep apnea.

Yes, BiPAP is inconvenient. But it's better to suffer the inconvenience of BiPAP than the illness and disability that can be caused by sleep apnea.

Sleep apnea is a condition in which breathing completely stops, for a few seconds up to about a minute, during sleep. Sleep apnea is usually accompanied by snoring, but it is not the same as snoring. In most kinds of sleep apnea, a loud snore or snort restarts breathing when the brain senses falling oxygen levels in the bloodstream.

Snoring is caused by the vibration of soft tissues at the back of the throat behind the tongue. The tissues include the soft palate, which is the pliable muscle tissue at the back of the roof of the mouth. They also include the uvula, the pear-shaped structure hanging down from the palate behind the tongue. The uvula plays a role in speech. It is also responsible for the gag reflex that initiates vomiting and for keeping food from coming up through the nose and maintains the flow of air into the lungs. Snoring also causes vibration of the tonsils, and is louder when the tonsil are inflamed. In snoring the muscles lining the air passageways stay tight, but in obstructive sleep apnea these muscles around an affected airway passage relax while sleeping occurs.

Snoring is most noticeable during dream or REM (rapid eye movement) sleep, when muscles relax. Obstructive sleep apnea prevents non-REM or deep sleep. Every time breathlessness is interrupted by a snore or a snort, the person who has sleep apnea goes back into REM sleep. Snoring does not cause noticeable reduction in the amount of oxygen reaching the bloodstream, but obstructive sleep apnea can cause drastic reduction in the amount of oxygen reaching the bloodstream.

People who have sleep apnea don't completely wake up at the end of each of the up to 500 episodes of breathlessness and snoring that can occur every night. They just don't get NREM (non-rapid eye movement) sleep because of the constant interruption caused by the snore or snort that restarts breathing.

NREM sleep is the time the brain organizes the memories of the previous day. It's also the time that the pituitary gland makes growth hormone, which protects the muscles and the immune system. During NREM sleep the brain recycles the hormones that trigger appetite and creates the hormones that tell you when you are full.

When these functions don't occur during six or seven hours of uninterrupted sleep, the result is an inability to learn new skills and difficulty dealing with stress. Muscle growth is slower, but fat storage is easier. And many people who develop sleep apnea also develop high blood pressure, heartburn and gastroesphageal reflux disease, sexual dysfunction, and obesity. Sleep apnea makes weight gain easier and weight gain makes sleep apnea more severe. Deprivation of NREM sleep also causes a tendency toward emotional outbursts and inattention that leads to accidents.

In obstructive sleep apnea, the passage of air from the nose and throat become blocked so that air does not enter the lungs. There are several locations that can become blocked, but most often the soft palate fails to keep the tongue from falling back into the throat. The intracostal muscles in the diaphragm keep trying to bring air into the lungs until the brain sends a message to wake up—just a for a moment, just long enough to get the tongue out of the throat. This brief interruption of sleep is essential to restart breathing, but cancels out the benefits of NREM sleep.

In central sleep apnea, the muscles in the diaphragm don't keep moving, so air does not flow in through the nose and mouth, even if the passageways of the upper respiratory tract are unobstructed. In mixed sleep apnea, there is an initial period of central sleep apnea. Lower air pressure causes the tongue to fall into the throat, causing obstructive sleep apnea. When a little breath makes it way past the obstruction, the result is "not enough air," or hypopnea.

Stopping snoring doesn't hurt. Your bed partner will appreciate it, and you make get slightly better sleep. But sleep apnea is not just about snoring. A Breathe-Right strip, for example, helps keep the nostrils open, but it can't do anything about obstruction of the throat by the tongue and it can't restart diaphragm muscles. Treating sinusitis and nasal obstruction improve air flow and reduce snoring, but they also don't have any effect on obstruction of the throat or the neurological problems that cause central apnea.

The single best indication that you may have sleep apnea is being informed by a sleeping partner (or by a member of your family who sleeps in a nearby room) that you have long periods of breathlessness at night that are ended by a loud snore or snort. If you sleep by yourself, the almost-certain signs of sleep apnea include:

• Snoring yourself awake once or more every night.
• Waking up feeling tired even though you have spent eight hours in bed.
• Heartburn in the middle of the night that does not occur at any other time.
• Waking up with a dry mouth. And most importantly,
• Waking up feeling that your are fighting for breath or suffocating.

If you have these symptoms, you almost certainly have sleep apnea, but you will still need to see a doctor for diagnosis and treatment. Other signs of sleep apnea include throwing off the covers even when the bedroom is not overheated, morning headache, memory lapses, and inattention. Adults who have sleep apnea often need to get up to urinate in the middle of the night, as increased blood pressure sends more blood through the kidneys. Children who have sleep apnea may wet the bed. ADHD in children is also sometimes associated with sleep apnea.

The only approved surgical technique for sleep apnea in the United States is a procedure known as uvulopalatopharyngoplasty. The surgeon removes part of the uvula and all of the palate, then sews the edges together. It gets lasting results but it is intensely painful for several days.

Several oral appliances are used to relieve the severity of apnea. They are discussed in more detail on the page Oral Appliances for Sleep Apnea.

Traditional sleeping pills and tranquillizers relax the muscles. Lying on your back puts pressure on your throat that is not counterbalanced by tension in the throat muscles, causing the airway to collapse. These medications may also reduce the strength of the signal from the brain to the intracostal muscles in the diaphragm to power breathing, aggravating or sometimes even triggering central apnea. Drinking alcoholic beverages may have a similar effect.

We breathe in oxygen and we breathe out carbon dioxide. Sleep apnea usually is not fatal because sensors lining the arteries can detect rising carbon dioxide levels and send a message to the respiratory centers in the brain, which it turn send a message to the muscles in the diaphragm to cause the lungs to inhale air. If the action of the diaphragm does not result in lower carbon dioxide levels, then the brain sends an alarm signal that temporarily wakes us up so any obstruction is at least temporarily removed.
This mechanism is based on blood carbon dioxide levels, not blood oxygen levels.

Sometimes the system does not work. Morphine may stop the sensors from sending the high-carbon dioxide message to the brain. Alcohol, tranquillizers, or sleeping pills may interfere with the action of the brain's respiration centers. If the muscles in the diaphragm are weak, they may not be able to create the snore or the snort that removes the obstruction to the airway. When the heart is weak, so little oxygen may circulate that the body does not create enough carbon dioxide to activate the alarm signal.

The most dangerous coexisting condition for sleep apnea is congestive heart failure. In a research study in China, researchers found that 30% of men who had both sleep apnea and congestive heart failure died within 2 years.

Sleep apnea deprives the bloodstream of oxygen. The heart tries to ensure that the brain gets the oxygen it needs by pumping harder and faster. At first high blood pressure is only a problem at night, but it may spill over into waking hours.

Sleep apnea can cause high blood pressure that increases the risk of strokes and heart attacks, and when strokes cause damage to the breathing centers of the brain and heart attacks cause congestive heart failure, they can cause sleep apnea.

you aren't abducted by extraterrestrials and then beamed back to a nearby location, there is a good chance that your symptoms are related to sleep apnea. People who don't get enough sleep at night may experience microsleep during the day. For a fraction of a second to a few seconds they "blank out" their environment. This can cause accidents, but sometimes it just cancels out any conscious memory of short-term events. However, these symptoms can also be caused by a condition called narcolepsy, so medical diagnosis is necessary. It's best to see your doctor before you have a serious accident.

And on a related topic,

No, the two conditions are unrelated. Nighttime sleep deprivation caused by sleep apnea, however, may lead to microsleep incidents that mimic narcolepsy.

This story has been going around since Dr. Stasha Gominak, who is a licensed physician who practices in Tyler, Texas, where a number of MDs use nutritional supplements in treating various diseases, released a video in which she claimed that vitamin D could cure sleep apnea. Most people who have tried her suggestions have not noted improvement in their sleep apnea.

It is well established that people who have sleep apnea usually have low vitamin D levels, but it is not established that taking vitamin D cures sleep apnea. It could be that people who feel tired during the day simply don't get as much time in the sun so their bodies don't make as much vitamin D. For now, taking up to 10,000 IU of vitamin D per day probably won't help sleep apnea, but it won't hurt, either.

You should consult your physician, but the answer is usually yes. The reason is that the higher you travel, the less oxygen there is in the air. Your body receives less oxygen with each breath, and in extreme cases your brain could become so poorly oxygenated that it would not send the signal to "kick start" your breathing with a snore. There are things your doctor can do for you besides giving you a prescription for an oxygen bottle, such as giving you a prescription for a medication called acetazolomide, that also help. It actually helps to sleep in a room heated with a fireplace, since the carbon dioxide released by the burning wood raises bloodstream concentrations of carbon dioxide and stimulates breathing.

Everyone develops sleep apnea at an elevation of 7600 meters (25,000 feet). Most people develop sleep apnea at an elevation of 5000 meters (16,500 feet). When the problem is low oxygen at high altitude, however, the time between snoring events is shorter, usually just 12 to 34 seconds, instead of the full minute of breathlessness that is experienced by people who have sleep apnea at lower altitudes.

Yes. Most people will have more incidents of sleep apnea when the air pressure is low, especially during stormy weather.

Cardiac pacemakers usually do not cause sleep apnea, but vagus nerve pacemakers for chronic pain disorders, post-traumatic stress disorders, seizure disorders, Parkinson's disease, obsessive-compulsive disorder, and eating disorders sometimes do.

Home sleep studies can measure breathing effort, blood oxygen levels, snoring, head and neck movement, and airflow. Together, these measurements are enough to diagnose obstructive sleep apnea. The problem is that they are not enough to diagnose mixed sleep apnea or central sleep apnea, and they will not capture neuromuscular problems that cause interruptions of REM sleep. To make sure all your sleep issues are addressed, your doctor will prefer to do your sleep study in a sleep laboratory.

The American Academy of Sleep Medicine (AASM) approves home sleep studies only when:

• The patient is between 18 and 65 years of age. Younger and older patients are referred to the sleep laboratory.
• There is a high probability that the patient has moderate to severe obstructive apnea. The AHI score that measures the number of sleep apnea events per hour is more accurate when patients are able to sleep all night. It is easier to sleep without being hooked up to electrodes.
• There are no indications of any other sleep problem, such as restless legs syndrome, circadian rhythm disorder ("sundowning" in older people), or extreme obesity interfering with the movements of the chest muscles.
• There are no other major medical problems. People who have diabetes and/or high blood pressure typically will be allowed to take home sleep testing if they meet the other criteria, but people who have congestive heart failure or any neuromuscular disease will not.

Almost no one gets a good night while wearing electrodes in a sleeping cap. Many people have trouble falling asleep when they know they are being watched. It's not unreasonable to be concerned about doing something embarrassing while asleep. As long as some sleep is recorded in each of the various stages of sleep, however, the doctor should be able to make an accurate diagnosis. The process is not perfect, but it is sufficient for the doctor to prescribe treatments that will help you sleep better.

The sleep technician counts incidents of apnea, complete cessation of breathing, and hypopnea, shallow breathing that last at least 10 seconds. Hypopneas occur when airways allow some air to pass despite their being partially blocked. Apnea can last up to two minutes, and hypopnea can last up to ten minutes.

The technician will calculate the total number of apneas added to the total number of hypopneas observed during the entire sleep study and then divide that sum by the total number of hours of sleep. The resulting number is known as the apnea-hypopnea index or AHI. This index number is used to measure the severity of sleep apnea. An AHI of 5 or less is considered normal. An AHI of 5 to 15 represents mild sleep apnea, 15 to 30 is moderate sleep apnea, and more than 30 is severe sleep apnea. Sometimes the AHI is 100 or higher.

A respiratory effort related arousal, or RERA, is a change in brain activity caused by repeated struggles to continue breathing. The brain is aroused from deep sleep but does not become fully awake. A RERA typically lasts no longer than 15 seconds, and there is no recollection of them the next morning. Each RERA, however, interrupts deep sleep. RERAs can be measured in the sleep lab but they cannot be measured in home testing.

The second sleep study is conducted to "titrate" continuous positive airway pressure, or CPAP. This procedure involves wearing a small face mask through which a machine blows air to prevent airways from closing. CPAP is started at low pressure that is increased until it stops sleep apnea. Different people require different CPAP settings, depending on the severity of their apnea, how much they way, the narrowness of upper airway passages, and the "floppiness" of the palate and tonsils. A sleep study can also be conducted to determine whether an oral appliance works or not.

Overnight pulse oximetry uses a sensor attached to a finger or an earlobe to monitor oxygen levels through the night. It is an alternative to a blood test that requires tapping an artery in a hand, which is a painful and unpleasant procedure.

Sometimes episodes of sleep apnea cause respiratory effort related arousals but do not last long enough to cause hypoxia, lower bloodstream oxygen levels. Sleep apnea may be causing fatigue without causing circulatory problems. Also, conditions other than apnea can cause low oxygen levels. Sometimes overnight pulse oximetry is used to ascertain whether CPAP is correcting low oxygen levels after the patient has been on the treatment for several months.