It took me a while to find some time to write here. But I did some research these days and here are my results:
I found a lot of clinical studies in favor for using oximetry as an effective way to diagnose and monitor sleep apnea, and I didn't find any study who can sustain your observation "Many apnoea sufferers do not desaturate. "
It is pointless to post here all the links from these studies, because no one will have so much time to read them all. But if someone insists...I saved most of them in a document.
However, I will post one study about the effectiveness of oximetry for sleep apnea diagnosis: http://www.ncbi.nlm.nih.gov/pubmed/17283346
TITLE: Diagnosis and initial management of obstructive sleep apnea without polysomnography: a randomized validation study.
ABOUT: Polysomnography (PSG), despite limited availability and high cost, is currently recommended for diagnosis of obstructive sleep apnea and titration of effective continuous positive airway pressure (CPAP).
68 patients with a high pretest probability of moderate to severe obstructive sleep apnea (apnea-hypopnea index [AHI] >15 episodes/h) identified by sequential application of the Epworth Sleepiness Scale (ESS) score, Sleep Apnea Clinical Score, and overnight oximetry.
RESULTS: In the initial management of patients with a high probability of obstructive sleep apnea, PSG confers no advantage over the ambulatory approach in terms of diagnosis and CPAP titration. The ambulatory approach may improve adherence to treatment. When access to PSG is inadequate, the ambulatory approach can be used to expedite management of patients most in need of treatment.
Tens of clinical studies come to the same conclusion. As for the remark with "Many apnoea sufferers do not desaturate", a study says that using unstandardized oximeters can influence the interpretation of sleep apnea severity. So it might be less, or more. It depends on the oximeter's quality, user's knowledge, etc... This study is on my list, so if you really want to read it, please let me know. I forgot which one it is, so I have to test each link.
This investigation took me almost 2 hours, but I hope it's worth it.