This sleep study guide will help you better understand the numbers and data presented from your sleep study.
1. Time Scale: Across the top is the bar indicating what time it is during the night. It is written in a 24-hour clock format; for example, 2300 is 11:00 pm, and 0500 is 5:00 am.
2. Stage Plot: This section of information, a combination of thick and thin black lines, shows your stage of sleep by looking at brainwaves. W=awake, and is the very top line. 1 & 2 are light sleep; 3 is deep sleep. REM is rapid eye movement sleep, which is also known as dream sleep. REM sleep is indicated by the thick black line. On average, most people have between 3-5 REM sleeps per night.
3. Transient Arousals: These are “mini-brain wakeups,” and this section also looks at your brainwaves. Each red vertical line means that something happened to jolt your brain to the “awake” switch for a few seconds—for example, a noise in the room or an episode of sleep apnea. This is a great way to look at how much sleep you are getting; if you have lots of “mini-brain wakeups,” your sleep is very interrupted and not usually refreshing.
4. SaO2: This line represents the amount of oxygen in your bloodstream throughout the night. “Perfect” oxygen is a reading of 100%; we want at least an oxygen reading of 95%. An oxygen reading of at least 90% is the lowest amount of oxygen that will still keep all parts of your body from getting the oxygen it needs. Anything lower than 90% means that your body is operating in a “low oxygen environment,” meaning that organs like the brain, heart, and kidneys are not getting enough oxygen—not a good thing.
5. Apneas/Hypops: This section registers the number of times your upper airway actually collapsed shut (also known as apneas, or “no breathing”) and the number of times your upper airway got very narrow and restricted (also known as hypopneas, or “little/shallow breathing”). It is normal to have a few of these during the night, but they should average out to be less than 5 events per hour. The markers along the side indicate to the physician the specific type of airway closure or narrowing that is occurring.
6. Snores: This line measures your snores. Each vertical line is one snore.
7. Limb Mvmnt: This line shows the number of leg kicks you have throughout the night. Each vertical line is one movement, twitch, or kick.
8. Position: This line shows an estimate of what position you were lying in at a given point in the night. Up indicates that you were awake and up in the room (for example, a bathroom break). Further designators of position are right side, left side, belly, and back.
9. Heart Rate: This line shows the number of times your heart beats per minute; also known as your heart rate. Normally, a healthy person’s heart rate ranges anywhere from 60-100 beats per minute (bpm); this varies based on the medications you are on, how much you are moving at a given time, and what type of cardiovascular shape you are in (athletes and very fit people have lower heart rates). When we sleep, it is expected to be at the low end of normal, or even below; for example, a healthy, fit person can have a heart rate of 50-60 bpm while sleeping.
Medically reviewed by Mark Reploeg, MD, Sleep Medicine