Understanding Your AHI Score: A Complete Guide

What Is AHI?

AHI stands for Apnea-Hypopnea Index — it's the single most important number in your CPAP therapy. It measures how many breathing disruptions you have per hour of sleep.

Your CPAP machine calculates AHI automatically every night by counting two types of events:

• Apneas: Complete pauses in breathing lasting at least 10 seconds
• Hypopneas: Partial reductions in airflow (at least 30% reduction) lasting at least 10 seconds

The formula is simple:

AHI = (Total Apneas + Total Hypopneas) ÷ Hours of Sleep

For example, if you had 12 events over 6 hours of therapy, your AHI would be 2.0.

What's a Good AHI Score?

AHI Range	Classification	What It Means
Under 5	Normal	Your therapy is working well
5 – 15	Mild	Room for improvement — check mask fit and settings
15 – 30	Moderate	Therapy needs adjustment — talk to your provider
Over 30	Severe	Contact your sleep physician promptly

Most sleep physicians consider under 5 the target for effective CPAP therapy. Many well-treated patients achieve AHI under 2.

Types of Events in Your AHI

Not all respiratory events are the same. Understanding the breakdown helps you and your doctor fine-tune treatment.

Obstructive Apneas (OA)

Your airway physically collapses, blocking airflow. This is what CPAP primarily treats — positive air pressure acts as a pneumatic splint to keep your airway open. If you're having many obstructive apneas, your pressure may need to be increased.

Central Apneas (CA)

Your brain temporarily stops sending the signal to breathe. These are not caused by airway obstruction, so increasing CPAP pressure won't help (and may worsen them). Central apneas can be related to sleep stage, medications, altitude, or sleep position.

Hypopneas (H)

Partial airflow reduction — your breathing becomes shallow but doesn't stop completely. These are the most common events for most CPAP users.

RERAs (Respiratory Effort-Related Arousals)

Very subtle breathing disruptions that cause a brief awakening. RERAs are not included in your AHI (they're counted in a separate metric called RDI), but they can still fragment your sleep.

Why Your AHI Changes Night to Night

It's completely normal for AHI to vary. Common factors include:

• Sleep position — Back sleeping typically produces more events
• Alcohol — Even moderate drinking relaxes throat muscles and increases events
• Allergies and congestion — Nasal congestion can increase mouth breathing and leaks
• Mask fit — A leaking mask means the machine can't maintain proper pressure
• Weight changes — Even small weight changes can affect airway anatomy
• Sleep stage — REM sleep naturally produces more airway relaxation

How to Improve Your AHI

1. Ensure a good mask seal — This is the #1 factor. If your mask leaks, your therapy is compromised. Replace cushions regularly (every 1-3 months).

2. Use your CPAP all night — Therapy is most effective with 7+ hours of use. Taking the mask off at 3am means you're unprotected during late-night REM sleep.

3. Check your pressure settings — If your AHI is consistently above 5, discuss pressure adjustments with your provider. Auto-adjusting (APAP) machines adapt in real-time.

4. Manage nasal congestion — Use your CPAP humidifier, consider saline rinse before bed, and treat allergies.

5. Sleep position — Side sleeping reduces obstructive events for most people.

How to Read Your AHI Data

Your ResMed machine stores detailed AHI data on its SD card. While the machine's screen shows a basic summary, tools like CPAP Clarity let you see the complete picture — including event types, timing, and trends over time.

Analyze your CPAP data for free →

Understanding your AHI is the first step to better sleep therapy. Track it consistently, look for patterns, and work with your provider to optimize your treatment.