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 possiblities to list them here.

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.

Dr. Smith: OK, here are some articles, Ross.
1. http://ajrccm.atsjournals.org/cgi/content/full/163/6/1294 (not compared to CPAP)
2. SLEEP 1995;18:501-10 Oral Appliances For The Treatment Of Snoring And Obstructive Sleep Apnea: A Review
Summary: This paper, which has been reviewed and approved by the Board of Directors of the American Sleep Disorders Association, provides the background for the Standards of Practice Committee’s parameters for the practice of sleep medicine in North America. The 21 publications selected for this review describe 320 patients treated with oral appliances for snoring and obstructive sleep apnea.
3. http://findarticles.com/p/articles/mi_hb4345/is_3_35/ai_n29337679 (compares to CPAP)
4. http://www.journalsleep.org./ViewAbstract.aspx?pid=26465 Oral Appliances for Snoring and Obstructive Sleep Apnea: A Review
Abstract:
We conducted an evidence-based review of literature regarding use of oral appliances (OAs) in the treatment of snoring and obstructive sleep apnea syndrome (OSA) from 1995 until the present. Our structured search revealed 141 articles for systematic scrutiny, of which 87 were suitable for inclusion in the evidence base, including 15 Level I to II randomized controlled trials and 5 of these trials with placebo-controlled treatment. The efficacy of OAs was established for controlling OSA in some but not all patients with success (defined as no more than 10 apneas or hypopneas per hour of sleep) achieved in an average of 52% of treated patients. Effects on sleepiness and quality of life were also demonstrated, but improvements in other neurocognitive outcomes were not consistent. The mechanism of OA therapy is related to opening of the upper airway as demonstrated by imaging and physiologic monitoring. Treatment adherence is variable with patients reporting using the appliance a median of 77% of nights at 1 year. Minor adverse effects were frequent whereas major adverse effects were uncommon. Minor tooth movement and small changes in the occlusion developed in some patients after prolonged use, but the long-term dental significance of this is uncertain. In comparison to continuous positive airway pressure (CPAP), OAs are less efficacious in reducing the apnea hypopnea index (AHI), but OAs appear to be used more (at least by self report), and in many studies were preferred over CPAP when the treatments were compared. OAs have also been compared favorably to surgical modification of the upper airway (uvulopalatopharyngoplasty, UPPP). Comparisons between OAs of different designs have produced variable findings. The literature of OA therapy for OSA now provides better evidence for the efficacy of this treatment modality and considerable guidance regarding the frequency of adverse effects and the indications for use in comparison to CPAP and UPPP.
Citation: Ferguson KA; Cartwright R; Rogers R et al. Oral Appliances for Snoring and Obstructive Sleep Apnea: A Review. SLEEP 2006;29(2): 244-262.

5. http://www.springerlink.com/content/j4w6r21256314131/fulltext.pdf Review of oral appliances for treatment of sleep-disordered breathing
Abstract Between 1982 and 2006, there were 89 distinct
publications dealing with oral appliance therapy involving a
total of 3,027 patients, which reported results of sleep studies
performed with and without the appliance. These studies,
which constitute a very heterogeneous group in terms of
methodology and patient population, are reviewed and the
results summarized. This review focused on the following
outcomes: sleep apnea (i.e. reduction in the apnea/hypopnea
index or respiratory disturbance index), ability of oral
appliances to reduce snoring, effect of oral appliances on
daytime function, comparison of oral appliances with other
treatments (continuous positive airway pressure and surgery),
side effects, dental changes (overbite and overjet), and
long-term compliance