Dr. Smith: PLMD often accompanies sleep disordered breathing. However, since his AHI and SpO2 are relatively normal, these movements do not appear to be related to his breathing at all. One movement every minute of the night is very excessive, and since he is also aroused out of normal sleep architecture every 2 minutes, I have to think this is affecting his sleep, even though he does not admit to sleepiness.

I have picked up early Parkinsons in a patient like this, so I am a bit sensitive to the issue, and would discuss a referral to rule this out if he was may patient. As the sleep MD is a pulmonologist, and not a neurologist, he would be less likely to make the connection. However, hopefully, I am just an alarmist, and the patient has little to worry about. Maybe you can make him an appliance for his snoring, then get him retested to see if the PLMD has improved. Let me know how it goes!

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: That is an excellent and thought-provoking (for me) question that has me wondering who came up with the 90% rule and how did that become the standard CMCP (conventional morbidity cut point) accepted in the field of sleep. It is oft quoted, and almost all sleep software talks about the time spent under 90%, but after some surfing, I have not yet been able to find out why they chose this many years ago. When they study hypoxemia, they use the time under 90% to define nocturnal hypoxemia.

In a study on dialysis, the abstract states “It is well established that nocturnal hypoxemia in sleep apnea causes an inversion of the circadian arterial pressure rhythm and triggers nocturnal hypertension.”

In a study on advanced cancer, The Prevalence of Nocturnal Hypoxemia in Advanced Cancer they quote:
“Nocturnal hypoxemia was defined as SaO2 < 90% for 2% of the monitored nighttime." They further state "Of 100 patients, 35 had nocturnal hypoxemia. These were more likely to have lung disease (P < 0.05), a lower forced expiratory volume in one second % predicted (P = 0.01), lower daytime SaO2 (P = 0.01) and higher levels of mental fatigue (difficulty concentrating) (P = 0.02), compared to those without nocturnal hypoxemia.

In a study on pulmonary hypertension, they quote “Patients who spent > 10% of the total sleep time with oxygen saturation by pulse oximetry (Spo2) at < 90% or who needed oxygen to maintain their Spo2 level at > 90% were classified as nocturnal desaturators.”

Basically, it is well accepted that 90% is the cut point, but I am still unaware of the original source. I will continue to search, and thanks for the question!

Dr. Smith: I realize this is the least expensive screening method, and it’s better than nothing, as the oxygen saturation closely follows (as a rule) apneic events. However, this is misused by many health practitioners. I received a report from an ENT who used pulse oximetry, but with this specific patient, he desaturated to 77% and stayed under 90% for 42 minutes. The ENT stated that the patient needed no further study, did not need CPAP and that an oral appliance was the best thing. In my opinion, that is malpractice.

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.