Sleep study
To confirm a diagnosis of obstructive sleep apnea, you must participate in a sleep study. During a study, your sleep is monitored. The subsequent data is evaluated by a sleep specialist.
Testing for apnea falls into two general categories: polysomnography and limited channel monitoring.
Polysomnography
Polysomnography is the simultaneous recording of multiple physiologic signals during sleep. The signals generally included are: brain waves (electroencephalogram, or EEG); eye movements (electrooculogram, or EOG); chin muscle activity (chin electromyogram, or EMG); air flow from the nose and mouth; chest and abdominal movement; blood oxygen levels (oximetry); heart rate and rhythm (electrocardiogram, or ECG); and leg movements (leg electromyogram, or EMG). The EEG, EOG, and chin EMG signals are necessary to determine whether a person is awake or asleep, and also to determine whether his or her pattern of sleep is normal. For an example of the kind of data that can be collected in a sleep lab, visit the Sleep Lab Interactive and check out the apnea example.
Polysomnography is usually performed in a sleep laboratory with monitoring by a sleep technician. In people with OSA, polysomnography recordings demonstrate repetitive episodes of breathing pauses despite efforts to breathe (see Figure 6). It is considered the “gold standard” for diagnosis.
Advantages of polysomnography include the following:
Technician is continuously present to adjust signals for optimal recording
Sleep is recorded
Other sleep conditions may be observed
Disadvantages are:
Recording is performed in an unfamiliar environment
More expensive than limited channel monitoring
Limited Channel Monitoring
With this test, monitors record a smaller number of physiologic signals than during polysomnography. Generally the signals are focused on breathing and blood oxygen levels. With these monitors alone, sleep cannot be precisely determined but can be estimated by recordings of body movement (actigraphy). This test is usually performed in the home in the absence of a sleep technician, but sometimes it is used in a sleep laboratory setting. Increasingly, people who have a high likelihood of OSA and have few other medical conditions are tested via limited channel monitoring. This method is also used for follow-up testing of people with OSA, to determine whether their treatments are effective.
Advantages of limited channel monitoring:
Signals are obtained in a more normal sleep environment
Costs are lower than with polysomnography
Disadvantages are:
Technician is not available to ensure high-quality recordings
Greater failure rate, which can require repeat study
Sleep is not recorded
Other Diagnostic Tests
Sometimes other tests are done in addition to polysomnography or limited channel monitoring. However, by themselves, the following tests are inadequate to confirm a diagnosis.
Oximetry: This is a method of recording blood oxygen levels alone. It is not a substitute for either polysomnography or limited channel monitoring because low blood oxygen levels can be caused by disorders other than OSA. In addition, some people with OSA have little reduction in blood oxygen levels.
Sleep Questionnaires and Diaries: These provide useful information to understand a person’s sleep habits and patterns. However, by themselves they are insufficient to confirm or exclude the diagnosis of OSA.
Blood Tests: There is no blood test for OSA. Some tests, like thyroid hormone level tests, may allow a healthcare practitioner to determine whether an associated medical condition is present.
Why do I need a sleep study?
Your doctor has ordered a sleep study due to a concern that you may have a sleep disorder that is affecting your health. The goal of the study is to obtain data that will help the physician determine the next steps in your care. The most common type of sleep problem, sleep apnea, is a disorder in which your breathing is irregular at night. This causes stress on your heart, which can lead to low oxygen levels, hypertension, and heart rhythm problems. It may also lead to increased plaque build-up in your arteries of the heart and brain, and is associated a higher risk of stroke and heart attack.
Not all people with apnea have sleepiness during the day or insomnia at night. Some people may have other symptoms such as morning headache, fatigue, weight gain or worsening memory. Even if you are unaware of any breathing problems, you may still have sleep apnea if you do not sleep well.
What is measured during a sleep study and why?
While you are sleeping, your body physiology is different from when you are awake. As a result, we need to take several different measurements during the sleep study including heart rate, breathing, sleep level (as measured by the EEG on your scalp), oxygen levels, and movement. These measurements help us determine the causes of your sleeping problem. For example, some people may have abnormal brain waves during sleep that prevent them from reaching the expected types of sleep stages. Their brain waves may be affected by movement, which in turn may be affected by respiration. It is important to evaluate how each of these different factors interact.
What kind of sensors will be used to measure my sleep during the study?
There are no invasive measurements required during the sleep study unless your physician specifically orders something. Most of the sensors used in a sleep study are attached to the skin or on the surface of your body. An exception is the sensor prongs that are placed in your nose to measure the air flow coming in and out. EKG patches are placed on your chest to measure your heart rate. Similar patches are placed on your legs and arms to measure movement. About ten electrode patches are attached to your head with glue to detect your brain waves and sleep level. You may have some glue residue in your hair after the study that will be removed with a cleansing solution in the morning.
We will have you wear some elastic bands around your chest to measure how your chest moves while you breathe. A sensor that is taped on your finger measures oxygen levels. Naturally, you may find sleeping with all these sensors is not as comfortable as sleeping in your normal bed. We expect that your sleep will be somewhat disturbed while being tested, but even if you sleep for only a few hours, we will be able to gather a great deal of information that will be useful.
What kind of room will I be in for the sleep study? What if I need to use the bathroom?
You will be given a private sleeping room with a private bathroom and shower for the night of the sleep study. You will have a television in your room which, you can use prior to the start of the sleep study. Although the study is inside the hospital, you will not be sleeping in a regular hospital room. The room in the sleep laboratory is more private than most hospital rooms, and is in a separate part of the hospital. If you need anything during the night, you can call out and the technicians will hear you on the intercom. They can also assist you if you need to use the bathroom.
Will the bed and pillows be comfortable?
The lab has standard beds that are designed to meet the qualifications for hospitals. Pillows, blankets and sheets are also standard. If you are particularly sensitive to pillows and bedding, you are welcome to bring your own pillow and comforter.
Can I control the temperature of my room?
Each room is equipped with its own thermostat, which can be adjusted according to your request. Please let the technician know if you prefer to have the room hotter or cooler.
Does it matter if I do not sleep well during the study?
The sensors and the new environment are likely to make you feel less comfortable than when you are at home and you may not sleep as well. However, even if you sleep for only a few hours we should be able to gather a great deal of information. It only takes a few hours of sleep for a breathing disturbance such as apnea to be detected, even with less restful sleep.
Will the technician wake me up during the study?
We will try to avoid waking you, but it is possible that the technician will need to do so in order to fix some cables or replace some of the sensors that might fall off. As mentioned previously, we do not expect this night to be entirely typical for you, but we can collect a lot of information within a few hours and sometimes the issues may be obvious early in the study.
If we find that you have a breathing disturbance that meets the criteria for severe apnea within the first two hours of sleep, the technicians may try to give you some treatment. They will wake you up and place a mask on your face that will help blow air into your nose or your mouth. This intervention only occurs if you meet certain criteria and if we are certain that you do not have other options for therapy.
Should I take my usual medications on the night of the sleep study?
Yes, you should take your usual medications on the night of the sleep study unless otherwise indicated by your doctor. You will need to bring any medications you take at night since we will not be able to order them from the pharmacy. If your doctor orders any special medication for you to take on the night of the sleep study, please bring it with you.
Does it matter what position should I sleep in during the night of the study?
Our goal is to collect the best data we can about you while you sleep. To do this, we will want to see you sleep in your usual positions, but we may also ask you to sleep in other positions as well. Some people have severe problems with apnea when they sleep on their back, but none when sleeping on their side. If you have only been sleeping on your side during the study, the technician may come into the room at some point and ask you to try to sleep on your back. If you never sleep on your back or can’t sleep in that position, we will not require it for this study.
Should I drink alcohol on the night of the sleep study?
If you usually drink alcohol more than twice a week, then it is probably a good idea to drink the same amount of alcohol on the night of your study. Alcohol affects nighttime breathing and it is best for us to be able to measure your sleep in its most vulnerable state to determine how it is disturbed. If you drink semi-regularly, then drink your usual amount, and have a friend or family member drive you to the sleep study. You should not drink and drive to the lab.
When will I get the results of the sleep study?
The results of the sleep study are not immediately available.
