Q: I was able to get a copy of my sleep study from my doctor, but I don’t understand what I am looking at. Can you tell me what these numbers mean?
Dr. Smith: I read 2 or 3 of these every day, and rarely do they resemble each other. However, I can help with some of the acronyms and numbers even without seeing the study.
AHI: Stands for the Apnea-Hypopnea Index. Very simply, this means the number of times you stop (or significantly hinder) breathing for at least 10 seconds every hour. These “events” can be due to an obstruction or due to your brain’s respiratory center being a bit lazy.
RDI: This stands for Respiratory Disturbance Index. There is some controversy here, but generally this number is derived from adding the RERAs to the AHI. So, the RDI should always be higher than the AHI.
RERA: Respiratory Effort Related Arousal. These do not need to last 10 seconds, but they are related to an obstructed breathing effort that created a sleep arousal. If you have many RERAs but a low AHI, this is called Upper Airway Resistance Syndrome (UARS)
ODI: Oxygen Desaturation Index. This is generally considered to be the number of times per hour that your oxygen became desaturated at least 4%. This usually occurs concurrently with or shortly after a respiratory (breathing) interruption, or apneic event.
If you (or anyone) would like to know more about the numbers or acronyms on your sleep study, just let me know. There are far too many possibilities to list them here.