AHI Calculation
The AHI for this patient is 5.8 events per hour, calculated by dividing the total number of respiratory events (35) by the total sleep time in hours (6), which classifies as mild obstructive sleep apnea. 1
Calculation Method
The Apnea-Hypopnea Index (AHI) is defined as the sum of apneas and hypopneas per hour of sleep. 1
For this patient:
- Total apnea episodes: 10 1
- Total hypopnea episodes: 25 1
- Total respiratory events: 35 1
- Total sleep time: 6 hours 1
- AHI = 35 events ÷ 6 hours = 5.8 events/hour 1
Severity Classification
According to the American Academy of Sleep Medicine criteria, this AHI of 5.8 falls into the mild OSA category (AHI 5-14 events/hour). 2
The standardized severity thresholds are: 3, 2
- Normal: AHI 0-5 events/hour
- Mild OSA: AHI 5-14 events/hour (this patient)
- Moderate OSA: AHI 15-29 events/hour
- Severe OSA: AHI ≥30 events/hour
Important Clinical Caveats
The AHI alone may not fully capture the physiological stress of sleep-disordered breathing, as it does not account for the duration or morphology of individual respiratory events. 4, 5, 6 Patients with similar AHI values can exhibit significantly different cardiovascular stress related to their disease, with correlation between AHI and obstruction severity parameters showing only moderate agreement (r²=0.604). 4
Longer duration apnea and hypopnea events lead to deeper oxygen desaturations and greater physiological stress, yet paradoxically may result in a lower AHI if events are prolonged enough to reduce their frequency per hour. 4, 5 This means two patients with identical AHI values of 5.8 could have vastly different clinical severity depending on whether their events last 10-15 seconds versus 30-40 seconds. 4, 6
The definition of hypopnea significantly impacts AHI calculation, with the American Academy of Sleep Medicine defining hypopnea as a ≥30% reduction in airflow for ≥10 seconds associated with either ≥3% oxygen desaturation or an arousal. 2 Some respiratory limitations lasting 5-10 seconds with associated desaturation may be clinically significant but excluded from standard AHI calculations. 7