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Low PulseOx
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Ok, this isn't a medical forum, and I take all the caveats that this therefore will come with.

Over the last few years I've done occasional PulseOx tests off the back of a Samsung phone. Then late last year I got a dedicated finger PulseOx monitor. 6 weeks ago I got a FR955 and have it set to read overnight. Finally, I'll add a few readings at my Doctors as part of just routine test.

I do have very mild asthma, I'm 47 with a RHR of low/mid 40s at the moment, and according to Garmin a respiratory rate of 12 in daytime and drops to 8 overnight. My wife has always complained that she gets freaked when I seems to stop breathing in my sleep. Never really seemed to be an issue to me. I think/thought it was related to my large lung volume - tested as part of my asthma diagnosis.

Anyway, back to the question. I'd always kinda ignored the pulseOx readings from the spot tests - typically in the 90-94 range. I just put that down to the skin on my finger or equivalent impacting the readings. Now with the benefit of consistent readings from the Garmin that shows that 90-92% and dropping to high 80s over night then I'm wondering if there is an issue here with me more than the readings. Note that this is now 4 separate machines reading the PulseOx as consistently lower than normal.

However, these low readings continue through the daytime too, so not 'just' sleep apnea. The low Resp rate and heart rate don't match the medical descriptions either. So is there anything here to be concerned about?
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Re: Low PulseOx [Duncan74] [ In reply to ]
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I have seen similar-ish with my 955 readings. I normally get readings in the 98%-100% range during the day on my 955 and Apple Watch with spot readings. My overnight Pulse Ox with the 955 is in the low 90s (91-93 range). My RHR is around 45 and my sleeping respiration rate is 12-15. have not researched it, but my armchair theory is that everything slows down at night and my body is only processing the oxygen it needs while in max relaxation, so Pulse Ox is low but not representative of my system when processing normally.
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Re: Low PulseOx [exxxviii] [ In reply to ]
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Yeah, but in my case I'm NEVER seeing anything above 95%. Even on a daytime if I do a finger PulseOx or force the FR955 to do one I'll get a 92-94%
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Re: Low PulseOx [Duncan74] [ In reply to ]
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Sounds like you may have sleep apnea, if your wife notices that you stop breathing. Given that we're on this particular forum, I'll assume you're not obese, but don't let that fool you. Yes, plenty of fit, lean, competitive athletes suffer from sleep apnea. Worth getting checked out.
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Re: Low PulseOx [Duncan74] [ In reply to ]
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Yeah, that is different. That is doc worthy to more completely understand.
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Re: Low PulseOx [Duncan74] [ In reply to ]
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Duncan74 wrote:
Ok, this isn't a medical forum, and I take all the caveats that this therefore will come with.

Over the last few years I've done occasional PulseOx tests off the back of a Samsung phone. Then late last year I got a dedicated finger PulseOx monitor. 6 weeks ago I got a FR955 and have it set to read overnight. Finally, I'll add a few readings at my Doctors as part of just routine test.

I do have very mild asthma, I'm 47 with a RHR of low/mid 40s at the moment, and according to Garmin a respiratory rate of 12 in daytime and drops to 8 overnight. My wife has always complained that she gets freaked when I seems to stop breathing in my sleep. Never really seemed to be an issue to me. I think/thought it was related to my large lung volume - tested as part of my asthma diagnosis.

Anyway, back to the question. I'd always kinda ignored the pulseOx readings from the spot tests - typically in the 90-94 range. I just put that down to the skin on my finger or equivalent impacting the readings. Now with the benefit of consistent readings from the Garmin that shows that 90-92% and dropping to high 80s over night then I'm wondering if there is an issue here with me more than the readings. Note that this is now 4 separate machines reading the PulseOx as consistently lower than normal.

However, these low readings continue through the daytime too, so not 'just' sleep apnea. The low Resp rate and heart rate don't match the medical descriptions either. So is there anything here to be concerned about?


I'm curious. Are you at altitude?

While I don't consider my Garmin a medical device, it does always agree with the doctor when I am there. I've never seen numbers that low except at high altitude or with sickness. I generally report a stable level from 96 - 98%. The lowest has been 92 or 93 maybe when I'm unwell. I have diagnosed asthma as well, but uncertain about sleep apnea.

My wife has told me for years that sometimes I stop breathing. After checking back, my watch seems to register that. Its very sporadic though and I've never pursued a sleep study because I feel like I sleep well.
Last edited by: turdburgler: Aug 14, 22 18:12
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Re: Low PulseOx [Duncan74] [ In reply to ]
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Disclaimer here: I am an MD, anesthesiologist to use the American lingo, and obviously dealing with oxygen saturations and that applied physiology on a daily basis.
Firstly: agree, this does not sound quite normal. I would personally be ignoring the Garmin and Samsung readings and using the monitor from your doctors surgery as the best indicator of what your true readings are. The cheap finger sensors that have become more popular with COVID are OK, but still the calibration can be a bit out of whack and you never quite know what your real value is.
Secondly: That data, combined with what your wife has said, is enough information to really warrant having a formal sleep study done. Google the STOP BANG score and enter your own data and see what score you generate....it will probably say you are at intermediate risk and therefore a sleep study is likely to be indicated. This will show whether you do in fact have sleep apnea, which could be leading to a whole raft of other issues. You will not stop breathing in your sleep simply from having a decent lung capacity etc.
This is something to take up with your family doctor as there are potentially all sorts of causes of a lower SpO2 reading during the day like you are getting. But this would be dependant on your age, overall health and any other specific medical co-morbidities. If you are training OK and not feeling unusually out of breath etc then it would be unusual for this to be occurring during the day secondary to significant pathology (assuming, as has been asked, that you are not at altitude). To understand why that is requires an understanding of the oxygen-haemoglobin dissociation curve and why your oxygen levels have to drop a fair bit before we start to see desaturation as such (technically the partial pressure of oxygen in your blood).
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Re: Low PulseOx [Duncan74] [ In reply to ]
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Work-up for hypoxia (or relative hypoxia) is a bit sophisticated. But big picture, there are few key issues to think about. And I am going to think out loud. So take this with grain of salt. Seek a formal evaluation. And hopefully eveyone reading sees this more as physiology class than "what could be wrong with me?"

Breathe in, oxgen goes into your lungs, into your alveoli, the air sacs that are filled with gas (mixture of O2 and CO2 among other gases). Lungs are sponges that absorb the oxygen. Venous blood is passing from right heart -> to the lungs -> through the pulmonary capillaries to pick up the oxygen -> returns to the left heart oxygenated -> and then gets pumped out to the systemic arterial circulation. Deliver your oxygen, return to venous system, back to right heart, back to lungs, repeat.

Sat probes detect oxygen concentration in your arterial circulation, bound to your hemoglobin. If your O2 saturation is low, numerous possiblities. Where is the defect? Is it mild, moderate, severe? And is it transient or persistent?

I am going to presume for this discussion that you don't have a major cardiac or pulmonary dysfunction. Same for most people following,

What you describe sounds mild and more persistent. One plausible explanation for you is your asthma. People with asthma can have airway inflammation/narrowing/obstruction all the way down to their distal, small airways. This can cause some people to have air trapping, +/- some excess mucus. What that means is you don't fully exhale all of your gas, which can impair O2 reabsorption in those distal alveoli. Can lead to slightly lower O2 concentration.

Another very common explanation is some sort of shunt. Shunt is where venous, deoxygenated blood somehow gets mixed into the arterial circulation, thus lowing the arterial oxygen concentration. A patent foramen ovale (failure to close a communication between right and left atria at birth) can cause small shunt. This occurs and is normal in 15-25% of people (depending on the literature). Next, Arterial-Venous malformations. A tangle of venous-arterial capillary beds where for some reason the veins and artery blends and venous blood mixes with arterial blood in that malformation. This puts a small amount of venous blood into the arterial circulation. They can occur various places. People can have random AVM's in the lungs (I actually have a few small ones, and my baseline O2 saturation lives at 94-95%). Cirrhosis and liver disease causes shunts. Many people often have mild shunts and may not know.

Whatever the cause, sleeping can make baseline hypoxia, transiently worse. When you sleep, you lay on your lungs, can get some very mild atelectasis (airways and alveoli can collapse), and then periodic shallow breathing while asleep can lead to some hypoventilation. Which will take someone with mild hypoxia, and make it a little bit worse. This often ties in with sleep apnea.

Obstructive sleep apnea is transient, when sleeping, It is a structural problem. When people fall asleep who have it, their airway occludes, most often from crowding or collapse of soft tissue in the posterior pharynx. Inhalation brings O2 in, then the airway occludes, which inhibits passive exhalation, which then leads to lack of another respiratory effort, which then leads to O2 levels to drift down until your brain tells you don't die, and you startle, wake up and start to breathe again. There are also episodes of low or shallow respirations that can occur in sleep apnea. This hypoventialtion also contributes to low O2 levels.

These are the very common and not overly concerning causes of hypoxia. Again, separate from a more concerning cardiopulmonary diagnosis. There also weird genetic issues and hemoglobinopathies. I am not going to cover those.

I would say make sure you are evaluated. Consider Pulmonary Function Testing (or repeat if you have had in past), and Arterial Blood Gas to get an accurate measurement of your arterial concentration, calculate an A-a gradient, and then determine role for further studies. To include a screen for sleep apnea, and potential formal sleep study.
Last edited by: WannaB: Aug 16, 22 0:21
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Re: Low PulseOx [turdburgler] [ In reply to ]
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turdburgler wrote:

I'm curious. Are you at altitude?

While I don't consider my Garmin a medical device, it does always agree with the doctor when I am there. I've never seen numbers that low except at high altitude or with sickness. I generally report a stable level from 96 - 98%. The lowest has been 92 or 93 maybe when I'm unwell. I have diagnosed asthma as well, but uncertain about sleep apnea.

My wife has told me for years that sometimes I stop breathing. After checking back, my watch seems to register that. Its very sporadic though and I've never pursued a sleep study because I feel like I sleep well.

No, sea level 90% of the time (at work), about 130m altitude when upstairs at home. Although I travel a lot with work, it's almost all at sea level (coastal cities, Auckland, Wellington, ChCh, and Tauranga). Most of my run trails literally get wet when it's king tides.

And the consistency with the different devices, including the doctor/dentist as low 'point' data sources, and then the consistency with the last 6 weeks from the daily garmin is what's made me 'think'.
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Re: Low PulseOx [Amnesia] [ In reply to ]
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;-) Many thanks. From memory of past posts I was wondering/hoping that you'd chime in. I appreciate the response, and the nature of the way you present.

As above, no, not at altitude. As for the 'believe the medical practice' tool, that's what first made me start to wonder. I always paid little heed to the samsung one. But then the finger one I got last year seemed to agree. Still, not a particular issue. But then I paid a bit more attention to the levels at the dentist and then again, when I swapped to a new GP and they did the new patient test, mine was low (92%), but my wife who went in after - hers was 'normal' 98% meaning that the machine was working OK (big generalised leap, but seems likely).

Age 47, weight 24BMI, not at my fittest as a result of soem biomechanical injuries overlast couple of years, but able to hold a FTP of 290w at moment (down from c330w 2 years ago) and currently running sub 50min 10kms,( down from sub 45mins). Peak flow is over 700 so asthma fairly well controlled (88kg, 1.93m tall). So all up I'd say I'm in fair shape overall.

The Stop Bang was 4 - High Risk. (although some versions of the test have 4 as intermediate)

OK, so based on this seems like I need to have a chat with my GP. Nothing particularly worrying in all I've seen, but worthy of a chat with the doc all the same.

(FWIW I was 30 when I was diagnosed with Asthma. I'd spent my whole life just assuming my wheezing was because I was fat and unfit. Was pointed out after my first Ironman I really wasn't either of those.....)
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Re: Low PulseOx [Duncan74] [ In reply to ]
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Duncan74 wrote:
;-) Many thanks. From memory of past posts I was wondering/hoping that you'd chime in. I appreciate the response, and the nature of the way you present.

As above, no, not at altitude. As for the 'believe the medical practice' tool, that's what first made me start to wonder. I always paid little heed to the samsung one. But then the finger one I got last year seemed to agree. Still, not a particular issue. But then I paid a bit more attention to the levels at the dentist and then again, when I swapped to a new GP and they did the new patient test, mine was low (92%), but my wife who went in after - hers was 'normal' 98% meaning that the machine was working OK (big generalised leap, but seems likely).

Age 47, weight 24BMI, not at my fittest as a result of soem biomechanical injuries overlast couple of years, but able to hold a FTP of 290w at moment (down from c330w 2 years ago) and currently running sub 50min 10kms,( down from sub 45mins). Peak flow is over 700 so asthma fairly well controlled (88kg, 1.93m tall). So all up I'd say I'm in fair shape overall.

The Stop Bang was 4 - High Risk. (although some versions of the test have 4 as intermediate)

OK, so based on this seems like I need to have a chat with my GP. Nothing particularly worrying in all I've seen, but worthy of a chat with the doc all the same.

(FWIW I was 30 when I was diagnosed with Asthma. I'd spent my whole life just assuming my wheezing was because I was fat and unfit. Was pointed out after my first Ironman I really wasn't either of those.....)

Thanks for the feedback, happy to help.
I should have stuck with anaesthetist, being a kiwi as well!
It certainly sounds like whatever may be causing your Sp02 to be reading low is not likely to be anything super serious given what you are able to train and hold cycling and running wise.
It is not surprising that your STOP BANG gets a score of 4, it is a screening tool and something you can take to your GP to have a sleep study organised. I think the more we look into obstructive sleep apnoea, the more we find it and the more hidden damage we see that it is doing.
WannaB mentioned your asthma as a potential cause, from experience this would be highly unusual in someone fit and well and otherwise asymptomatic, and it really is because of the shape of the oxygen-haemoglobin dissociation curve. Looking after people with asthma and airways disease on an almost daily basis in theatre, it is unusual that we have anyone present electively for surgery with an Sp02 of >97%, it is only occasionally that we see levels much lower than this and they tend to be in patients who have a long history of lung disease and are not in the best of health overall. Quite unlike the way you function.
As WannaB mentioned, pulmonary function tests (PFTs) and an arterial blood gas (ABG) are also useful for figuring out the cause of the lower saturations, the sleep study is more for the obstructive sleep apnoea side of things!
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Re: Low PulseOx [WannaB] [ In reply to ]
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Wow, many thanks for that - as an engineer this 'how the machine works' stuff is fascinating to me.

As above, and as per your opening - point taken and I will engage with my primary healthcare provider.

Regarding the sleep - my wife reports not that I breath in a shallow way, quite the opposite, I tend to take a breath, then it gets held for ages, and she worries I've stopped breathing, and then I breathe out and then a big breath in, and hold again. So the opposite of the shallow breaths. I do suddenly wake up in the night sometimes though with a 'ok, need to breathe' reaction and feeling like I do when we do breathwork in swim squad (no or 1 breath lengths).

I've never had any of these things tested. My heart has been investigated due to bradychardia (sp, sorry) where in my 30s my RHR was in the upper 30s - 72hour monitor and some other scans/tests. But nothing on this.
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Re: Low PulseOx [Amnesia] [ In reply to ]
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Amnesia wrote:
WannaB mentioned your asthma as a potential cause, from experience this would be highly unusual in someone fit and well and otherwise asymptomatic, and it really is because of the shape of the oxygen-haemoglobin dissociation curve. Looking after people with asthma and airways disease on an almost daily basis in theatre, it is unusual that we have anyone present electively for surgery with an Sp02 of >97%, it is only occasionally that we see levels much lower than this and they tend to be in patients who have a long history of lung disease and are not in the best of health overall. Quite unlike the way you function

Good point, and I think that is probably fair. Especially with how fit and asymptomatic you are. I should add that asthma physiology can in some circumstances increase diffusion capacity. Asthma is a wide spectrum, and if you carry that as a true diagnosis, with wheezing as you note, I think reasonable to factor that in somewhere. Not likely to be the sole explanation. Good luck.
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Re: Low PulseOx [Duncan74] [ In reply to ]
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Skin pigment (wrist readings and fingertip units), hair color/density (wrist readings), and nail polish (fingertip units) will affect accuracy of pulseox devices. Not sure if any of these might apply to you.
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Re: Low PulseOx [Duncan74] [ In reply to ]
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You've had some really great advice here, and I cannot improve upon it. I am finishing up EMT school right now as part of my role as a volunteer firefighter. I can tell you that if I responded to someone like you and measured SPO2 of under 93, I would definitely want you transported to the hospital to get checked out. And this is not a direct comparison, because I suspect when you are sleeping, you could be woken up pretty easily, but if I encountered an unconscious person with a resp rate of 8, I would definitely consider administering naloxone! That's just to say, 8 is not normal for most people, even when sleeping.

All of that is just to say, get it checked out. It's outside of normal so make sure there is not something you need to worry about.

Question - file this in the wild speculation by a lay-person category - did you have a rough case of COVID? I remember reading that some people with COVID had very low SPO2, like below 80, and did not feel out of breath at all. Perhaps some malfunction in the chemoreceptors measuring ph/co2 of the blood? Could this be a long COVID symptom?

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Ed O'Malley
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Founder of VeloVetta Cycling Shoes
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Re: Low PulseOx [Duncan74] [ In reply to ]
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I am similar, low I guess. Usually 90-94 on my Garmin fenix 6 watch.
I wear the watch on the bottom side of my wrist to keep from scraping it, I will try it the other way...

I have year round allergies, and am usually stuffy at night and in the morning.
Lots of workouts where my nose does not breathe in that well, especially at the start.
Would these allergies lower my numbers?

58 years old, fit cyclist, do some swimming , little old man weights, and foolishly still playing basketball.
I live at 2800 feet. I will ask my doctor ahead of my yearly to see if he has any thoughts.

Now I am worrying a little.

Rob
Last edited by: robmitchell: Aug 15, 22 11:21
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Re: Low PulseOx [WannaB] [ In reply to ]
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I thought of a shunt as well. OP, let us know what your doc says.
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Re: Low PulseOx [RowToTri] [ In reply to ]
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MKB wrote:
Skin pigment (wrist readings and fingertip units), hair color/density (wrist readings), and nail polish (fingertip units) will affect accuracy of pulseox devices. Not sure if any of these might apply to you.
Pasty white english guy that first got exposed to sunlight aged 35 when I moved to NZ. The bike club used to put me at the back in dusk as a safety feature so the drivers could see my glow in the dark white legs. Ditto the hair, whilst things have slightly moved on, for the first 10 years we were together my wife referred to my manly mane of chest hair as 'Bill and Ben" - yep she named the individual visible hairs. Only now by judicious use of theatrical glue am I able to transplant the increddible bushes from nostrils, eyebrows and ears to the rest of me to fake macho. Or to conclude, nah, I read and considered those before, but the combination and consistency of the wrist and finger readings, on different machines and different fingers/wrist locations makes me think that the other things are more of a factor.[/quote]


RowToTri wrote:
(Snip)...

Question - file this in the wild speculation by a lay-person category - did you have a rough case of COVID? I remember reading that some people with COVID had very low SPO2, like below 80, and did not feel out of breath at all. Perhaps some malfunction in the chemoreceptors measuring ph/co2 of the blood? Could this be a long COVID symptom?

I caught Covid in May, and so after there was a baseline of 92s. That's stayed similar post covid. I did drop to 85 on day 1 of covid, and I'll admit I felt not that bright - in hindesight if I'd understood what the numbers meant, what normal was, etc at that point I would have called a doctor instead of just staying in my hotel room on my own and hoping I recovered. That wasn't helped by being a numpty and catching it on a business trip where I was supposed to be on a single overnight and was flying carry-on and hadn't thought to take any of my asthma meds with me.... At 85% I was really panting and 'stressed'. Thankfully got my GP to send a prescription to a pharmacist in the town I was staying, then the pharmacist to deliver on to the hotel on their way home, and once the bricanyl was delivered I perked up. And so I am going to go out and say that the covid has brought a focus to me understanding that a long term 'feature' is something I should talk to my GP about.
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