Q: What does the RDI, AHI and ODI represent on the Watch-PAT report?

Dr. Smith: RDI stands for the respiratory disturbance index, which includes apneas, hypopneas and RERAs. If the RDI is high and the AHI is low, this indicates Upper Airway Resistance Syndrome, and most sleep centers will not report this on studies. Oral appliances are great for this condition.
AHI stands for the Apnea-Hypopnea Index, and contains apneas and hypopneas. Put simply, although not exactly correct, this is the number of times you stop breathing for at least 10 seconds each hour.
ODI is the desaturation index, and it means the number of times each hour your hemoglobin (storage facility and transporter of O2 in your blood) lets go of at least 4% of the O2 it contains. This is what you measure with your pulse oximeters you use when sedating patients.

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.

Q: Can an appliance be used with CPAP successfully?

Dr. Smith: At the same time? Yes, it’s called combination therapy, and
allows a CPAP user to have the pressure reduced to make it easier to
use. They can also be used alternately when they are hunting, on
airplanes, etc.. Of course, the right type of mask would need to be
used, and preferably one of the nasal cone type that does not place
any retrusive forces on the maxilla.

Another use for combination therapy is if you would like to prevent
any potential occlusal (bite) changes with the mandibular advancement
devices. If someone wears a MAD during the week, and CPAP on weekends,
for example, they will get no bite changes.