Apnoea-hypopnoea index (AHI)
The severity rating for your sleep apnoea is based on the average number of apnoeas and hypopnoeas you experience per hour of sleep. It is known as the AHI, or Apnoea-Hypopnoea Index. An apnoea occurs when your breathing stops completely; a hypopnoea is when you breathe less deeply than normal.
What is normal?
Most people have some apnoeas and hypopnoeas when they sleep. Fewer than five per hour is considered normal. With such a low AHI it is unlikely you would experience symptoms such as excessive daytime sleepiness.
What is abnormal?
If you are having five or more apnoeas or hypopnoeas per hour of sleep you will be diagnosed with sleep apnoea. With an AHI of five or above you are likely to experience:
- Symptoms of sleep apnoea, such as daytime sleepiness or lack of energy
- Complications of sleep apnoea, such as high blood pressure.
Mild, moderate and severe
Depending on your AHI score, your sleep apnoea will be classified as:
- Mild: 5 to 14 apnoeas or hypopnoeas per hour of sleep
- Moderate: 15 to 30 apnoeas or hypopnoeas per hour of sleep
- Severe: more than 30 apnoeas or hypopnoeas per hour of sleep.
The greater the severity of sleep apnoea, the greater the risk of complications. However, any diagnosis of sleep apnoea warrants lifestyle changes or treatment.
