What Do Your Sleep Study Results Mean?
You have had sleep disturbances that make it hard for you to get restful sleep, so your doctor recommended that you undergo polysomnography, commonly known as a sleep study. Now you’ve received your sleep study results based on the polysomnogram (PSG), but you have no idea how to interpret them. You can expect your doctor to give you the high points at your next visit, but it’s useful to have some sleep study knowledge of your own so that you can fully understand what the report saysand what your doctor is explaining to you.
The "What" and "Why" of Sleep Studies
When you underwent your sleep study, you were monitored overnight in the sleep clinic so that disturbances in your sleep throughout an entire evening could be monitored and captured. The sensors you were fitted with detected and measured various vital signs (such as blood pressure, heart rate, oxygen saturation and brain activity), as well as eye and limb movement, while you slept.
Each of these was measured and monitored for different reasons, and the results are collectively used to diagnoseor rule outsleep disorders, such as sleep apnea, restless legs syndrome and narcolepsy.
Here is an explanation of how some of the results may come together to indicate the source of your sleep difficulties.
Eye Movement, Brain Activity and Limb Movement
Measuring eye movement, brain activity and limb movement can help determine whether you are experiencing normal cycles of REM and non-REM sleep.
As you fall asleep, you enter a sleep stage called non-rapid eye movement (NREM), in which your brainwaves slow down. After around two hours, you enter rapid eye movement (REM) sleep. Your brainwaves begin to speed up, and eye movement is noticeable.
During a normal night of sleep, the average person experiences between four and six of these cycles, with the REM stage of sleep lasting longer in each successive cycle. Measuring brain activity can help determine whether your sleep disturbances are occurring in a certain stage of sleep, whether or not you are experiencing the normal amount of complete sleep cycles, and how severely a sleep cycle is being disrupted. These findings can help identify a variety of sleep disorder possibilities.
For example, the frequency of limb movements that occur within a given time period can help pinpoint a sleep movement disorder such as restless legs syndrome (RLS). Someone with restless legs syndrome often experiences twitches or jerks in the legs every fifteen to forty seconds while sleeping. These episodes can last a few minutes, or might last an hour or more. For some people, a single episode might last the entire night.M2> Blood Oxygen Level, Heart Rate and Breathing Rate
Measurements of blood oxygen level, heart rate and breathing rate are collectively used to diagnose sleep apnea, a disorder in which the body is periodically starved of oxygen, typically due to temporary airway obstruction. During an episode of apnea, breathing ceases for ten seconds or longer.
Experiencing more than five such episodes during a single hour of sleep is considered an indication of sleep apnea. Between five and fifteen episodes per hour is classified as mild apnea, fifteen to thirty is classified as moderate, and more than thirty events per hour is considered severe.
A blood oxygen level of less than 85 percent for more than half of sleep time is considered a threshold for severe sleep-related oxygen deprivation. Heart rate is somewhat variable, just as it is when awake, with most people averaging in the region of 60 to 70 beats per minute during normal sleep. Episodes of variation of up to eight beats per minute are normal.
Sleep latency measures how long it takes you to fall asleep, and it is used to help diagnose disorders such as narcolepsy and insomnia. A sleep latency average of less than five minutes (as measured over multiple episodes) can be an indication of narcolepsy.
Sleep latency is sometimes measured during a daytime sleep study. In this case, it’s assessed in conjunction with daytime sleepiness, a measure of how often you fall asleep involuntarily. Daytime sleepiness can be categorized as mild, moderate, and severe, depending on how disruptive it is in your daily life.
Talking With Your Doctor About Your Sleep Study
In most cases you'll be able to meet with your personal physician to review your sleep study results two or three weeks after the study. The intervening period is a good time to think about any further questions you want to ask your doctor about the study and the results.
Write questions down as they come to you to make sure you're well prepared to talk over any issues that concern you.
By: Emma Lloyd
The College of Physicians & Surgeons of Ontario. Clinical Practice Parameters and Facility Standards. Sleep Medicine 3rd Edition, September 2010 (revised January 2011). Available at http://www.cpso.on.ca/uploadedFiles/policies/guidelines/facilties/Sleep.pdf. Accessed: June 6, 2011.
Hensley MJ, Hillman DR, McEvoy RD (Chair), Neill AM, Solin P, Teichtahl H, Thompson BR, Tolhurst S, Thornton AT, Worsnop CJ, for the Australasian Sleep Association & Thoracic Society of Australia and New Zealand. Guidelines for Sleep Studies in Adults. Available at: http://www.sleepaus.on.net/guidelinesforadultsleepstudies.pdf. Accessed: June 6, 2011.
The Mayo Clinic. Polysomnography. Available at http://www.mayoclinic.com/health/polysomnography/MY00970. Accessed June 6, 2011.