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Understanding Apnea Hypopnea Index

Apnea Hypopnea Index is a method to record the number of hypopneas and apneas per hour. It is an important sleep study mechanism to determine the severity of sleep apnea.

Person suffering with severe sleep apnea are shortly awakened for almost hundreds of times every night due to low level of oxygen to the brain (Think about someone waking up every other minute and tapping on your shoulder.) leading to insufficient sleep and excessive tiredness during the day. To record these episodes, Apnea Hypopnea Index is used. This index calculates number of complete pauses (apneas) and partial obstructions (hypopnea) of breathing every hour of sleep.

Read Also: Sleep Apnea-Hypopnea Syndrome

apnea hypopnea indexBased on the Apnea Hypopnea Index, the sternness of OSA is categorized as follows:

  • Normal – AHI Less Than 5 per hour
  • Mild – AHI Between 5 to 15 per hour
  • Moderate – AHI between 15 to 30 per hour
  • Severe – AHI greater than 30 per hour

Along with AHI, RDI (Respiratory Disturbance Index) is also recorded. It not only includes apneas and hypopnea but also records subtle breathing irregularities.

Taking AHI as an Average

For instance let’s take AHI of 14.3 as an index, which is an average considered for one night. Now, it does not relate that you actually stopped breathing for 14.3 times at every hour of your sleep. You could be experiencing no hypopneas or apneas during few hours of the night, and then experience sudden breaks or pauses when REM was about to happen.

Most people experience hypopneas and apneas during REM (Rapid Eye Movement) sleep. REM is the sleep phase when we start dreaming. People usually have 3 to 4 cycles of REM sleep, with each REM cycle getting longer than the previous one. The first REM cycle starts after 1.5 hours after a person hits the bed and might have duration of 3 to 5 minutes—what if your wife suddenly wakes up? You could develop a large number of apnea and hypopneas each time when you’re entering the REM cycle. These arousals from deep sleep due to either apnea or hypopnea prevent your brain to get into REM phase of sleep and lead to excessive daytime sleepiness. So sleep disordered breathing isn’t just about a specific breathing disturbance but that are long enough for a person to be aware that he is awake.

Full Sleep Study with Apnea Hypopnea Index

apnea hypopnea indexIf you are having breathing difficulties in night even at a very small level, please consult your doctor for a complete study with AHI and RDI.

During the sleep study, sleep technicians will conduct a number of tests to detect any breathing problem during the night. A full sleep study records graphs through EEG (Electroencephalogram) to measure:

  • Breath intake pressure
  • Sinus pressure and temperature
  • Levels of carbon dioxide exhaled
  • Oxygen saturation levels

In addition to the above, your sleeping posture, pH balance in your throat and heart beats per minute will be assessed. During this full test, physician will also use Apnea Hypopnea Index and Respiratory Disturbance Index to analyze and understand the type of sleep disorders and frequency of pauses or obstructions in nighttime breathing.

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