AHI vs RDI

generally, all people experience sleep apneas one way or another. It’s just that there are some people who experience such more often than not. The result is a condition that is recognized as a disorder of sleep. Sleep apneas happen when there’s reduced or absence of breathing at sleep. Common in adults, this condition is diagnosed based on the patient’s medical background as well as after doing some tests. In this connection, there are two popular indices that are used to spot for this condition ‘“ AHI and RDI.
Apnea can also refer to the 4% reduction of oxygen in one’s blood. This is the immediate effect when one stops breathing, even for a short moment. Thus, oxygen is not transferred to the blood for circulation.
Apneas are measured usually over a period of two hours during one’s sleep across all sleep phases. Dividing the total number of apneas noted during this timeframe by the total number of sleeping hours will give the AI or apnea index. Obviously, the greater the AI value the more severe is the condition.
Hypopnea is an event wherein there’s just a sort of decrease in one’s breathing. Although this is not that severe compared to apneas, hypopneas is the breath amounting from 26 to 69% of one’s normal breath as opposed to apnea wherein it is 25% and below. Like the AI, you can also get the HI when you divide the number of hypopneas by the total number of sleeping hours.
With the two indices of AI and HI, one can arrive at the AHI or the apnea-hypopnea index. This is a combination measure of the two indices. Hence its formula is AI plus HI divided by the total hours of sleep.
The other combination index, often mistaken as a completely similar index to the AHI is the RDI. Completely known as the respiratory disturbance index, the RDI is the AHI plus all other phenomena that can disrupt sleep. These events do not fall under the definition of apnea and hypopnea but still cause some disruptions in sleep like the RERA (respiratory effort related arousal) i.e. snoring. The formula to get the RDI is (RERA + Hypopnea + apnea) divided by the number of testing hours
Sleep apnea is likely if the AHI reaches 15 times per hour, that is, granting that the patient doesn’t have any other existing medical conditions that may have resulted from sleep apnea. This is roughly one hypopnea or apnea every four minutes. In the presence of conditions like, hypertension, CHF (congestive heart failure), daytime sleepiness, mood disorders and insomnia, an AHI of 5 per hour is suggestive of sleep apnea. The value has been lowered because these patients may have already begun experiencing the symptoms associated with sleep apnea and that it is integral to commence treatment the soonest.
Once you have been diagnosed with sleep apnea, your doctor may prescribe one of the two methods for treatment which are the invasive approach and the non-invasive approach. The former entails an ENT surgery while the latter involved a form of nasal CPAP therapy.
In short, RDI is just the same as AHI but it includes the RERA or other occurrences that may disrupt sleep.

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