Sleep Apnea
In obstructive sleep apnea (OSA), the upper airway repeatedly narrows or collapses during sleep even though the chest is still trying to breathe. Each event can reduce airflow/oxygen and trigger a brief arousal, producing fragmented sleep that the sleeper may not remember.
The number to know: AHI
The apnea-hypopnea index (AHI) is the average number of complete or partial breathing obstructions per hour of sleep.
| Adult AHI | Conventional classification |
|---|---|
| <5/hour | normal |
| 5-14/hour | mild OSA |
| 15-29/hour | moderate OSA |
| >=30/hour | severe OSA |
An AHI of 60/hour means roughly one scored breathing event every minute and is well into the severe range.
AHI is useful but incomplete. Event duration, oxygen desaturation, sleep-stage distribution, arousal burden, symptoms, and cardiovascular/metabolic context can matter too.
Why CPAP works
CPAP is best imagined as a pneumatic splint. Continuous positive pressure keeps the collapsible upper airway open; it does not simply "breathe for you."
OSA can also distort sleep architecture by producing repeated arousals and more light sleep at the expense of consolidated deeper sleep.