Everything You Ever Wanted to Know About Sleep Studies But Were Afraid to Ask
A sleep study is necessary to determine if you have sleep apnea or other types of sleep disorders. An overnight test in a sleep lab monitored by a polysomnographic technician is the gold standard for sleep disorder diagnosis. Home test kits are an option for many people under the right circumstances.
During a sleep study in a sleep lab, you can expect monitoring of airflow, chest and abdominal movement, blood oxygen levels, muscle tone, arm and leg activity, brain activity and cardiac monitoring. Modern sleep labs have patients sleep in an environment that looks much like a hotel room. You will have various types of electrodes hooked up to your chest and abdomen, a sensor or cannula resting inside your nostrils, and a probe on a finger or toe to assess oxygen levels in your blood. The sleep lab staff do not stare at you all night long; they are watching monitors outside your room. A camera may be used to correlate data with your sleeping position during the night.
Sleep Lab Studies and Home Lab Studies
Sleep center studies can provide data from as many as 20 different sources of input about your breathing patterns, muscle activity, heart activity, and brain activity during sleep. Sleep lab studies are also able to differentiate changes in all these systems of your body during light sleep, deep sleep, and REM sleep. In short, sleep lab studies give a phenomenal amount of information and can really help physicians and sleep technicians clarify what is occurring, when, and why.
Home sleep apnea tests (HSAT), on the other hand, provide data about airflow obstruction, heart rate, and oxygen levels in the blood. If you have a home sleep study, you will wear a pulse oximeter during the night. The pulse oximeter probe fits over your finger or toe and uses a light to measure what percentage of your hemoglobin are saturated with oxygen molecules. The pulse oximeter also detects the pulse rate (heart rate). A circular band will wrap around your midsection. This band is called a thoracoabdominal monitor and it has electrodes on it that sense motion in your abdominal and chest regions. Finally, a cannula (small tubing) will rest just inside your nose. If you have worn a nasal cannula for oxygen before or seen one worn, that is basically what this sensor looks like. The nasal sensor detects airflow.
Home sleep tests record your oxygen saturation level and heart rate throughout the night. The monitor watches for airway obstruction by looking for pauses in airflow at the nose and by correlating these pauses with chest and abdominal activity.
Plug your nose and try to take a breath. Notice how your chest and stomach heave, but nothing happens. This is a demonstration of a full obstructive event: No airflow, lots of chest and abdominal movement, as muscles try to generate airflow.
Although home sleep tests do not deliver nearly as much data back to the physician as a sleep lab test, home tests have been proven to be very good for diagnosing moderate to severe obstructive sleep apnea (OSA) in patients with a high likelihood of having OSA based on their risk profile.
Although there are more than fifty types of sleep disorders, OSA is the most common sleep condition. For many patients, home sleep testing speeds up diagnosis and gets them connected to effective therapy quickly with cost-efficiency.
Good Candidates for Home Studies
Home sleep testing is not appropriate for anyone who has restless legs, marked insomnia, heart arrhythmias, or neurological issues. Home sleep tests can confirm obstructions but do not identify respiratory-related arousals.
Home sleep testing is best used as a tool to confirm obstructive sleep apnea in patients in whom it is likely present based on their symptoms and risk profile.
The STOP-BANG assessment tool created at the University of Toronto is used by physicians and other clinicians to identify people at risk of moderate to severe sleep apnea. Many hospitals use this tool, or something similar, to screen people before surgery. If the answer is yes to at least three of these questions, extra steps may be taken to monitor the patient for airway obstruction after anesthesia.
STOP-BANG (Follow the link to screen yourself on the official Stop-Bang site)
- Observed pauses in breathing or choking/gasping
- Pressure, high blood
- BMI >35
- Age >50
- Neck >16 (woman) or >17 (man)
- Gender - male
If you can answer yes to at least three of these questions, and do not have other sleep-related issues, cardiac issues, or neurological issues, then an at-home sleep study may be a great option for you. The Center for Medicare and Medicaid approved home sleep studies in 2009 as appropriate for the diagnosis of uncomplicated obstructive sleep apnea. back to top
Five Tips to Get the Best Results from A Home Sleep Study
At home studies are less expensive and more convenient than a sleep lab study. Testing in your bed gives results relevant to how you sleep every day. The wait time to get a sleep lab appointment is often months or more. A home study may also be a great intermediate step to get therapy started while waiting for a more complete evaluation.
If you are scheduled for a home sleep study, you can expect to receive a kit with all the supplies you need, an instruction sheet, and a number to call if you have questions. You will put the cannula in your nose, the pulse oximeter on your finger, and wrap the belt around your lower chest. Next, you turn the sleep monitor on and go to bed. Generally, home sleep apnea tests really are that easy to set up. Most kits do a bit of a pre-test to verify that all the input devices are working so that you are not wondering if all is well.
Hint 1: Remove any nail polish. Nail polish will interfere with the pulse oximeter's function.
Hint 2: Try to spend some time sleeping on your side and back. Obstructive sleep apnea gets worse in those two positions, and it can be helpful to know if a sleeping position greatly aggravates the condition.
Hint 3: Take note of the time you went to bed and when you got up again.
Hint 4: Avoid caffeine and alcohol so that you get a clearer picture of your baseline sleep breathing.
Hint 5: If possible, have someone peek in on you to make sure all the equipment is still hooked up and in a good position. Waking up in the morning only to discover you had pulled out the airflow sensors or taken off the pulse oximeter in your sleep would be very disappointing.
Understanding Your Home Sleep Study Results
AHI and SpO2 are the two key data points to focus on when you review your own home sleep study results.
AHI stands for Apnea-Hypopnea Index. AHI is a measure of how many times, on average, you had either an apneic event that lasted 10 seconds or longer or a hypopnea event. Hypopnea is just medical jargon for a breath (pnea) that is too shallow (hypo). Shallow breathing is a worry when it results in ineffective ventilation and oxygenation. The frequency of AHI events is a primary diagnostic indicator for OSA and is also used to classify the severity of the disorder.
|None/Normal||AHI is < 5 per hour|
|Mild||AHI is >= 5 per hour, but <15 per hour|
|Moderate||AHI >= 15 per hour, but < 30 per hour|
|Moderate||AHI >= 30|
SpO2 stands for peripheral oxygen saturation. It is measured by the pulse oximeter probe worn on the finger during the study. Pulse oximetry provides information about your heart rate and blood oxygen levels during sleep. Sleep lab testing usually also measures exhaled carbon dioxide (CO2). Although it is common to think that if we do not breathe effectively during sleep that our blood oxygen level will decline, truthfully a drop in oxygen is a very late sign of ineffective breathing. Exhaled CO2 levels rise much more quickly. Consequently, significant decreases in Sp02 at night are worrisome, especially if the value is sustained under 90%. If you have substantial, sustained drops in SpO2 during sleep, your physician may recommend that you go ahead and get a full sleep study completed at a lab.
Once you start sleep therapy, you can use your machine to know if you are getting enough support. Most modern CPAP and AutoPAP machines report your AHI from the night and trend it over time. Following your AHI can give you information to know if your therapy is sufficient enough.