Advanced concepts: Since sleep tests are not all equivalent, the learned society that defines sleep disorders has multiplied the indices according to the technology used. It's enough to make your head spin!

Initially, AHI was defined using the most comprehensive laboratory test, polysomnography with electroencephalogram (sensors on the scalp). Over time, it became clear that other respiratory abnormalities also explained the symptoms, and it is now recommended that these be taken into account when making a diagnosis using ITR or IPR. In summary, the respiratory disturbance index is the AHI plus those obstructions that cause more subtle difficulties in inspiration and brief awakenings of the brain without a drop in oxygen (high upper airway resistance HRVAS or Respiratory Event Related Arousal RERA).

If you take a first-generation home test (they use a cannula in the nose and do not measure sleep per se), you will use the respiratory event index (REI) rather than the AHI, which is the same concept except that sleep time is replaced by recording time.

With the latest generation of home tests (without nasal measurements), an ITR will be obtained and indexed with a "PAT" or "S" depending on the underlying technology.

However, the diagnosis must be based on clinical findings and the available index, the respiratory disturbance index (RDI) or RDI (and no longer AHI as in the past).

The final severity of obstructive sleep apnoea will be the most pronounced between clinical severity (determined by a doctor or nurse practitioner based on symptoms and health problems) and technical severity. Technical severity will be based primarily on the IPR or IER.

• Light: 5 to 15
• Moderate: 15 to 30
• Severe: 30 and above

Every test, regardless of its sophistication, has limitations and must be interpreted within its overall clinical context. No test, however accurate, can replace the clinical judgement of a doctor or specialist nurse.