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Why isn't oximetry a sufficient measure of sleep apnea?
#1
Why isn't oximetry a sufficient measure of sleep apnea?
Can the physiological harm of sleep apnea be attributed solely to oxygen starvation? If so, why isn't pulse-oximetry a sufficient measure, replacing the AHI summary statistic (for those of us who have this adjunct equipment)? Can an "area under the curve" number be derived or is it sufficient to count the number of episodes below some red-line, say SpO2 < 90.  

And what of the pulse rate data? Do regions of elevated pulse rate truly indicate REM sleep, and if that is a desirable property, should its extent be totaled as an index of improvement?

I say all this as a newbie, with horrible AHI's (which I attribute to mask leaking), but who nevertheless feels much better during the day! 
Of course I may be deluding myself, but my oximetry data look very clean.
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#2
RE: Why isn't oximetry a sufficient measure of sleep apnea?
A significant part of the harm from obstructive sleep apnea is related to intrathorasic pressure from trying to inhale against an obstructed airway. Positive intrathoracic pressure decreases left ventricular afterload and will augment left ventricular ejection. However negative intrathorasic pressure from obstruction during inspiration, will have the opposite effect and reduce left ventricular ejection. In patients with hypervolemic heart failure, this afterload reducing effect can result in improved left ventricular ejection, increased cardiac output and reduced myocardial O2 demand, but the increase in afterload can be crippling to the individual with low left ventricular ejection fraction. This pressure can lead to cardiac stress, a-fib, congestive heart failure and other less ominous conditions. In addition to the obvious problems with intrathorasic pressure, respiratory effort leads to arousals that disrupt sleep and lead to the common symptoms of fatigue, sleepiness, loss of concentration and malaise. While oxygen desaturation may accompany flow limitation, respiratory effort related arousal (RERA), hypopnea and apnea, it may miss many of these important, treatable conditions.

(post edited to reflect both positive and negative intrathorasic pressure based on a PM question)
Sleeprider
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#3
RE: Why isn't oximetry a sufficient measure of sleep apnea?
(11-15-2020, 10:40 AM)fredkahan Wrote: Can the physiological harm of sleep apnea be attributed solely to oxygen starvation?

No. There is the additional harm associated with sleep deprivation.
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INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#4
RE: Why isn't oximetry a sufficient measure of sleep apnea?
(11-15-2020, 10:40 AM)fredkahan Wrote: Can the physiological harm of sleep apnea be attributed solely to oxygen starvation? If so, why isn't pulse-oximetry a sufficient measure, replacing the AHI summary statistic (for those of us who have this adjunct equipment)? Can an "area under the curve" number be derived or is it sufficient to count the number of episodes below some red-line, say SpO2 < 90.  

Largely, yes.  The reduced oxygen availability produces a strain on all the systems and organs, not least of which are the heart and brain.  The brain consumes roughly 25% of your oxygen uptake at any one time.  It's by far the heaviest user.  The brain requires a sense of security, calm, and reduced activity, but also a circadian rhythm, to enter sleep and to derive the benefits from the ensuing stages.  Not just ensuing stages, but multiple cascades of them.  I am not familiar with any metric that uses the area under part of a curve to establish a diagnosis, but it doesn't mean the case hasn't been made.  It's just not promulgated by the industry.

And what of the pulse rate data? Do regions of elevated pulse rate truly indicate REM sleep, and if that is a desirable property, should its extent be totaled as an index of improvement?

Elevated pulse rate might mean REM, but it could also mean over-training effect for athletes, illness (flu, other diseases), and it could also mean a building de-sat.  You'd want to couple it, or associate it, with de-sats to establish that there is a deleterious condition and to then decide how to ameliorate that condition.  REM takes place cyclically, de-sats not so much.

I say all this as a newbie, with horrible AHI's (which I attribute to mask leaking), but who nevertheless feels much better during the day! 
Of course I may be deluding myself, but my oximetry data look very clean.

It is good that your oximetry is looking good.  The leaks are only an issue if they work against the machine and if you can link them to a chronic diminishment of treatment.  If the leaks awaken you, or leave you feeling less-than-easy about them, if you feel anxious or vexed by them, then you should probably deal with them constructively.  They will possibly affect your mood or your ability to place faith in your treatment and the machine.
Serial Tapist
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#5
RE: Why isn't oximetry a sufficient measure of sleep apnea?
Thanks! That was a thorough workout on cardiopulmonary physiology! The potential aggravation of congestive heart failure by intrapleural (intrathoracic) negative pressure extremes was new to me. 

Regarding the expectation of enhanced quality of sleep, I presently face the impasse that while under the masks I have used to date I have yet to achieve sleep at all!  But how would I really know? I wonder what hallmarks in the APAP or pulse oximetry traces are indicative of periods of sleep?
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#6
RE: Why isn't oximetry a sufficient measure of sleep apnea?
Determining sleep stage or quality from CPAP and oximetry data is not reliable. Some members use watches and other devices to monitor light or deep sleep. These work mainly on movement. It's not practical to hook up an EEG every night, so maybe the best advice is that your sleep is as good as you feel.
Sleeprider
Apnea Board Moderator
www.ApneaBoard.com

____________________________________________
Download OSCAR Software
Soft Cervical Collar
Optimizing Therapy
Organize your OSCAR Charts
Attaching Files
Mask Primer
How To Deal With Equipment Supplier


INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#7
RE: Why isn't oximetry a sufficient measure of sleep apnea?
(11-15-2020, 08:52 PM)fredkahan Wrote: Thanks! That was a thorough workout on cardiopulmonary physiology! The potential aggravation of congestive heart failure by intrapleural (intrathoracic) negative pressure extremes was new to me. 

Regarding the expectation of enhanced quality of sleep, I presently face the impasse that while under the masks I have used to date I have yet to achieve sleep at all!  But how would I really know? I wonder what hallmarks in the APAP or pulse oximetry traces are indicative of periods of sleep?
Sleeprider has answered you.  I use a Samsung Gear S2 Sport that records sleep, and also establishes a percentile score to rate efficiency.  Most nights I range between a low of 91% and often run up to 94/95%.  As SR says, the watches sense movement.  If you move once or twice in a three-five minute period, you're deemed to be 'restless', as my Samsung app tells me. Later, when I am immobile and apparently in a deeper level of sleep, the report shows graphically where I have been 'still' and in deeper sleep.  A few years back, when I was considering purchasing a fit/watch, the Fitbit and one other wrist-worn monitor were considered the top performers.  I believe that Apple and Samsung are currently right at the top, but the latest FitBit watch is also excellent.  As they improve and can convince health authorities of their efficacy, I can see them pairing changes in heart rate and breathing, or some other parameters, to make claims for REM sleep, in which case they'll be able to say how long you were dreaming.

Again, to emphasize what SR says, there is too often a disconnect between what our devices report to us on their displays, or what our morning's OSCAR reports says is the case about last night's 'rest', and how we actually feel.  This is a common complaint.  People find their reports saying they're getting excellent results from their therapy, but they feel, frankly, like crap.  Unfortunately, this can seriously erode the 'face validity' and the credibility that our machines should offer to us.  We counsel people to place a hefty amount of faith in the reports and to tough it out for the long haul.  But, we also acknowledge reports of persistent 'brain fog', feeling sleepy at inopportune times, being irritable, persistent headaches, and other complaints.  If we can offer some coaching to minimize those, we do so.
Serial Tapist
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#8
RE: Why isn't oximetry a sufficient measure of sleep apnea?
I'm glad you're feeling better during the day, but could you post a chart showing the horrible AHI? It sounds as though you're now sleeping with the machine, which is good, but perhaps we could help you see what's going on with the AHI.

A book you might enjoy is Why We Sleep, by Matthew Walker, a professor and researcher at UC Berkeley.
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#9
RE: Why isn't oximetry a sufficient measure of sleep apnea?
Many thanks to Mesenteria and Dormeo for their advice. I have just had very favorable experience with the AirFit F20 and will adopt it to complete my compliance runs and provide you with the results. I had in the past used the AirTouch cushions for both N20 and F20 but found them very irritating. The edges of the AirFit F20 cleverly conform tightly to my cheeks the moment it becomes inflated during the Mask Fit procedure, and of course the full face mask itself takes care of mouth puffing air leaks.

I need no convincing that a good night's sleep is precious. Quantitating it with FitBit-like devices sounds worth pursuing.
Regrettably, Walker's book (if not his entire opus) appears to have been savaged beyond credibility by Guzey and by the highly respected Andrew Gelman at Columbia.
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#10
RE: Why isn't oximetry a sufficient measure of sleep apnea?
Thanks for the links. Gelman's piece is very funny, though it begins by noting that "I’ve not read Walker’s book and I don’t know anything about sleep research, so I won’t try to judge Guzey’s claims. I read through and I found Guzey’s arguments to be persuasive, but, hey, I’m easily persuaded."

Guzey has no record of published research beyond a 2018 "bachelors thesis," a short column co-authored with Gelman with a focus on Walker, and a self-published "investigation" of the life sciences. His piece about Walker focuses almost exclusively on chapter one of the book.

None of this entails that Guzey is wrong in his criticisms, but I would not take them as gospel.
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