Measuring Sleep: the Sleep Study and Daytime Sleepiness

What polysomnography records

Polysomnography is the full overnight sleep study, usually done in a lab. A web of sensors records several streams at once so that breathing can be read against the backdrop of sleep itself.

1. EEG, eye, and chin sensors stage sleep — light, deep, and REM — and catch each brief respiratory arousal.
2. Airflow sensors at the nose and mouth detect apneas and hypopneas.
3. Chest and abdomen belts show breathing effort — the clue that separates obstructive from central events.
4. [[pulse-oximetry|Pulse oximetry]] on a fingertip tracks oxygen saturation through every dip.

Because the EEG knows when you are truly asleep, the lab can compute the AHI against real sleep time and tell apnea apart from quiet wakefulness. Simpler home tests record breathing and oxygen but not brain waves; they are convenient and often enough to confirm clear-cut obstructive sleep apnea, yet they can miss milder or mixed cases.

The daytime price of broken sleep

Every arousal drags you out of deep sleep for a moment. Stitch together hundreds of them and a full eight hours in bed delivers the rest of a far shorter night. The result is excessive daytime sleepiness: nodding off in meetings, fighting to stay awake at the wheel, foggy thinking, low mood. It is the most common daytime symptom of sleep apnea — and the one with real safety stakes.

To put a number on sleepiness, clinics often use the Epworth sleepiness scale: eight everyday situations, each rated 0 to 3 for how likely you are to doze. The total runs from 0 to 24, and higher scores flag a stronger tendency to fall asleep when you should be awake.

Epworth Sleepiness Scale — sample scoring

Chance of dozing (0 = never, 1 = slight, 2 = moderate, 3 = high)

  Sitting and reading ............................ 2
  Watching TV .................................... 3
  Sitting inactive in a public place ............. 2
  As a passenger in a car for an hour ............ 3
  Lying down to rest in the afternoon ............ 3
  Sitting and talking to someone ................. 1
  Sitting quietly after lunch (no alcohol) ....... 2
  In a car, stopped a few minutes in traffic ..... 1
                                                  ----
  Total .......................................... 17

Rough interpretation:
  0  to 10  ..... normal range
  11 to 24  ..... above-normal daytime sleepiness  <-- score 17

Note: the Epworth measures perceived sleepiness, not
severity of apnea. It guides discussion; it does not
diagnose on its own.