1. Your Apnea-Hypopnea Index (AHI)

The AHI is the single most important number in your sleep study report. It measures the average number of breathing interruptions — apneas (complete stops) and hypopneas (significant reductions in airflow) — per hour of sleep.

Here is how severity is classified:

Your physician will use the AHI alongside your symptoms and overall health profile to determine whether and what type of treatment is appropriate.

2. Types of Sleep Disruptions

Your sleep study does not just count apneas. It captures three distinct categories of disruption:

Apneas

A complete pause in breathing lasting at least 10 seconds. These are the most recognized characteristic of sleep apnea.

Hypopneas

A partial reduction in airflow — not a complete stop, but significant enough to lower blood oxygen or cause an arousal. Hypopneas are counted alongside apneas in your AHI score and can be just as clinically significant.

RERAs (Respiratory Effort-Related Arousals)

Partial airway narrowings that cause brief arousals from sleep without fully qualifying as apneas or hypopneas. RERAs fragment sleep architecture and can cause significant daytime fatigue even when AHI appears normal. They are often tracked in a related metric called the Respiratory Disturbance Index (RDI).

Sleep disruptions — regardless of type — have real short-term and long-term health consequences, from daily cognitive impairment to increased cardiovascular and metabolic risk.

3. Your Sleep Stages

A healthy night of sleep cycles through four stages multiple times:

• N1 (Light Sleep): The transition from wakefulness into sleep
• N2 (Established Sleep): Where most adults spend the majority of the night
• N3 (Deep / Slow-Wave Sleep): The most physically restorative stage — critical for tissue repair, immune function, and memory consolidation
• REM (Rapid Eye Movement Sleep): Where most dreaming occurs; essential for emotional regulation, learning, and memory

Sleep apnea fragments these cycles. Patients with significant sleep apnea often spend little or no time in N3 or REM sleep — which is why they wake feeling exhausted despite seemingly sufficient hours in bed.

Research has shown that AHI can actually worsen during REM sleep in many patients, meaning the deepest, most important stage of sleep is also the stage where breathing is most disrupted. Your report will note how much time you spent in each stage and in each body position (supine, lateral, prone).

4. Oxygen Desaturation (SaO2) Levels

Every time you stop breathing, your blood oxygen level drops. Your sleep study tracks these desaturation events continuously throughout the night.

Reference ranges:

• Normal: 96–99% blood oxygen saturation
• Mild desaturation: 90–95%
• Moderate desaturation: 80–89% — associated with cardiovascular stress
• Severe desaturation: Below 80% — can be dangerous; seen in severe untreated OSA

Your report will include your lowest recorded SpO2, the percentage of time spent below 90%, and your average nocturnal oxygen saturation. These numbers directly influence treatment decisions — particularly whether you may need supplemental oxygen alongside PAP therapy.

Effective PAP therapy restores normal airflow, which stabilizes oxygen saturation and eliminates desaturation events. Most patients see significant improvements in SaO2 within the first week of consistent CPAP or BiPAP use.

What Happens After Your Sleep Study Results?

Based on your report, your interpreting physician will typically recommend one of the following:

• CPAP or APAP titration if OSA is confirmed and moderate or severe
• In-lab titration study if a home sleep test was used and more detailed data is needed
• PAP therapy setup with a DME provider to get your equipment and learn how to use it
• Alternative evaluation if the results suggest central sleep apnea or a different sleep disorder

If you have questions about your results or are not sure which PAP device is right for you, our licensed Respiratory Therapist at My Respiratory Company can walk you through everything. Our $49.99 RT Consultation is designed exactly for this — reviewing your sleep study data and helping you make an informed, confident decision about your care.

Browse our CPAP and BiPAP devices — or continue learning with our guide on types of PAP therapy devices.