Scoring of hypopneas on NPSGs is, unfortunately not uniform. The sleep docs diagnosing us with SDB all believe hyponeas should be counted---or at least some hypopneas should be counted, but which ones should count still seems to be a bone of contention. Which is why we've got the confusing mess of the American Academy of Sleep Medicine (AASM) having two official definitions for scoring hypopneas: The AASM Recommended Standard and the AASM Alternative Standard for hypopneas. See http://www.ncbi.nlm.nih.gov/pubmed/19238801
for a scholarly discussion of how and when these two standards affect a patient's diagnosis of OSA as well as the formal definitions of the two standards:AASM Recommended Standard:
requires at least a 30% reduction in airflow for at least 10 seconds AND a corresponding O2 desaturation of at least 4%. Such a hypopnea does NOT require an EEG arousalAASM Alternative Standard:
requires at least a 50% reduction in airflow for at least 10 seconds AND one or both of the following conditions: A EEG arousal OR a corresponding O2 desaturation of at least 3%.
Of course, under both standards, the hypopnea has to occur during an epoch when the patient is ASLEEP according to the EEG evidence.
It's my understanding that Medicare requires hypopneas to be scored under the AASM Recommended standard, but that the folks working in sleep medicine are increasingly leaning towards believing that the arousals triggered by large numbers of "Alternative Standard hypopneas" can be just as damaging to the body as the O2 desats triggered by the hypopneas scored under the Recommended Standard. And it's also my understanding that some sleep doctors (such as mine) are deeply concerned that Medicare insists upon a 4% desat to score an hypopnea.
So my best guess is that your lab, like the lab where my diagnostic PSG was done, uses both rules, but distinguishes between them in the data. I've never seen my raw data--I had no luck in getting that released to me. But on the full summary report all of my hypopneas were listed as "hypopneas with arousal" (i.e. Alternative standard) and did not got into the computation of my (Medicare) AHI. In my case, I had a handful of OAs on that study, so my AHI was listed as 3.5, not enough to get an OSA diagnosis by Medicare standards. But with the 75+ hypopneas with arousal, my RDI = 23.1, and that got me formally diagnosed with moderate OSA because either the RDI or the AHI can be used to diagnose OSA. And my insurance company was perfectly willing to cover the cost of my treatment based on that study.