Obstructive Sleep Apnea (OSA) is a sleep disorder where your airway repeatedly collapses or narrows during sleep, blocking or reducing airflow even though your body keeps trying to breathe. Each blockage can last 10 seconds or longer and is often followed by a gasp, snort, or brief awakening as your brain signals you to reopen your airway.

Here’s the clinical picture, based on how sleep medicine defines and diagnoses it.

What causes the blockage

During sleep, the muscles in your throat relax. In people with OSA, this relaxation allows soft tissue at the back of the throat to collapse and block the airway. This can happen dozens or even hundreds of times a night.

How it’s measured

Sleep specialists use the Apnea-Hypopnea Index (AHI), which counts the number of breathing pauses (apneas) and partial blockages (hypopneas) per hour of sleep. The American Academy of Sleep Medicine (AASM) classifies severity this way:

• Mild: AHI of 5 to 14.9 events per hour
• Moderate: AHI of 15 to 29.9 events per hour
• Severe: AHI of 30 or more events per hour

How it’s diagnosed

According to both AASM and DSM-5 criteria, a diagnosis requires either:

• An AHI of 5 or more per hour, along with symptoms like loud snoring, gasping during sleep, daytime sleepiness, or witnessed pauses in breathing, or
• An AHI of 15 or more per hour, even without noticeable symptoms

Diagnosis is confirmed through a sleep study, either an in-lab polysomnography or a home sleep study