Sleep Study Explained

Sue cuddles Ryan before the sleep study begins

There was a comment yesterday asking what can be learned from a sleep study. It got me thinking; I realized that I didn’t really know completely. In Ryan’s comatose state, we simply wanted to know if he even experiences “sleep” as we know it, and go from there. I can tell you, this deeply scared me that he might not. That would not be good at all. So I did some investigation and research to see what else the study might provide.

Technical Mumbo Jumbo

First, for those of a more technical nature (which includes myself), a sleep study is called a polysomnography. The actual results are called a polysomnogram (or, PSG). The sleep study is a measure of many biological and physical responses (biophysical) that happen throughout sleep. Specific measurements are: brain waves (EEG), eye movements, facial movements, muscle activity (to include the skeletal muscles), heart rhythm (ECG), heart rate, breathing patterns and intensity, nasal and oral airflow, oxygen saturation, and vocalization.

Interpretation

A sleep technician analyzes data by evaluating the data in thirty second intervals. What I loved about the technician for Ryan is he was analyzing and updating the results in real time. He was very accommodating, answering all my questions throughout the night when I would pop out of Ryan’s room. The best is when he came into the room two hours into it and told me Ryan just had REM sleep! Yes!  You see, the first episode of “normal” REM occurs between sixty and 120 minutes from falling asleep.

Analysis Contents:

• Onset of Sleep. measured from the time the lights are turned off. This is called “sleep onset latency” and normally is less than twenty minutes.
• Sleep Efficiency. A simple calculation that takes the number of minutes of sleep divided by the number of minutes in bed. Normal is roughly 85% to 90%.
• Sleep Stages. These are based on three sources of data coming from seven channels: EEG (4 channels usually), Chin (1), and Eye Movement (2)

From this information each 30-second interval is scored as “awake” or one of four sleep stages: N1 and N2 (light sleep), N3 (deep sleep/slow wave), and REM. Stages N1, N2, and N3 are called non-REM sleep (hence the “N’ designation). The percentage of each sleep stage varies by age, with decreasing amounts of REM and deep sleep in older people. Most sleep is Stage 2. REM normally occupies about 20-25% of total sleep.

• Breathing Irregularities. Mainly apneas and hypopneas. I don’t think Ryan experiences these, but we might be surprised.
• Arousals. These are sudden shifts in brain wave activity caused by numerous factors (including breathing abnormalities, leg movements, environmental noises, etc). I know for certain that Ryan would experience these arousals when he heard me talking, adjusting his position, or fiddling with electrodes. There should be arousals, but not an abnormal amount, indicating “interrupted sleep” that could make him tired during the day.
• Cardiac Rhythm Abnormalities – I don’t anticipate Ryan having any.
• Leg Movements.
• Body Position.
• Oxygen Saturation – Ryan stayed above 95% the entire night.

What Next?

Once interpreted, the sleep physician writes a report which is sent to the referring physician (in Ryan’s case, this is IBRF). What I think would be especially useful (and will ask for) is to have this study performed throughout a normal day of activity in our home.