Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: vhfpmr on 26/03/2021 14:51:07
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Since covid made pulse oximeters toy of the moment, the published advice seems to be:
>=95%: You're fine.
92% - 95%: ask your doctor for advice.
<92%: Call 999.
So from this, it would appear that the higher the oxygen saturation the better, IE there's no 'optimum', nor any homeostasis striving to achieve it.
Of the pulse oximeters on the consumer market, it would appear that the accuracy of most, if not all, is ±2%, but professional machines don't seem to quote any accuracy at all in the specifications. So if your SpO2 were 93.5% for example, your course of action upon checking it with a pulse oximeter would be either do nothing at all or call an ambulance, depending only on whether your instrument lays at the top or bottom of its tolerance range.
I have a pair of oximeters, both the same model, and the difference between them is 1.16%, based on an average of 80 pairs of readings, which is well within tolerance, but the instantaneous difference between any one pair of readings is ±6%, so you might reasonably wonder whether they're of any use at all.
My own SpO2 is all over the shop, varying from 88% to 98%, but usually 93%. If I make an effort to breathe more deeply it will rise to 95%, but if I continue it then falls back to 93%, which rather seems to suggest that there's some sort of homeostasis at work. If I breathe hard enough for long enough it makes me go dizzy, which also suggests that more isn't necessarily better.
Any thoughts?
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The breathing reflex is prompted by a rise of carbon dioxide levels in the blood.
- That's why nitrogen asphyxiation is so dangerous, as it doesn't lead to increase in carbon dioxide in the blood.
You don't want to breathe too deeply for too long. Hyperventilation can cause dizziness, loss of vision and fainting.
It's also hard work, so your body does not naturally breathe too much.
See: https://en.wikipedia.org/wiki/Hyperventilation
Scarring of lung tissue due to COVID-19 infection reduces oxygen flow across the alveoli, and reduces blood oxygen levels.
- But because this scarring occurs gradually over a period of days to weeks, your body adapts to the reduced oxygen levels, and you may not notice it around the house
- You are more likely to notice it if you exercise; normal levels of exercise may leave you unusually breathless
- A pulse oximeter will pick up the reduced oxygen levels, even if you don't feel breathless
- This slow adaptation to reduced oxygen is similar to the process when mountain climbers spend a week or two at Everest base camp to acclimatize
With an average SpO2 of 93%, it sounds like you should mention it to your doctor, next time you visit.
- It SpO2 stays consistently below 92% (but you still feel ok), make an immediate medical appointment - a chest X-Ray will reveal if you have the "ground glass" pattern indicative of COVID scarring, or other respiratory problems.
See: https://en.wikipedia.org/wiki/Ground-glass_opacity
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I don't have/haven't had covid, it's another issue.
I've already been taken to A&E, but my SpO2 was 96-100% then.
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The trend of SpO2 is what saved my friend's life. As a fellow aviator he had a pulse oximeter in his flight bag for long trips above 10,000 ft. Realising that he had COVIDs symptoms he tracked his oxy sat over a couple of hours and realised it was trending increasingly downwards, so called an ambulance and spent the next 3 weeks in hospital.
IIRC 100% is an arbitrary figure assigned to 20-year-old athletes at rest, and used for the primary calibration of simple pulse oximeters. The reading you get at home depends on accurate and consistent positioning of the gadget and the quality of the clip mechanism - the full-blown hospital gadget has a very reproducible clip compared with the amateur devices, but any information is better than none.
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After engaging in this discussion, I bought a pulse oximeter today - the finger-clip type.
- Useful for home health monitoring, along with a thermometer and blood pressure monitor.
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The reading you get at home depends on accurate and consistent positioning of the gadget and the quality of the clip mechanism - the full-blown hospital gadget has a very reproducible clip compared with the amateur devices, but any information is better than none.
The stand-alone monitors have an expanding hinge, so they adjust for jaw spacing as well as angle, and fit very well. The clips that are integrated with the bedside monitors I've used in hospital are just like rubber thimbles, and don't fit very well at all. They seem designed primarily for easy cleaning.
Taking multiple readings from consecutive display updates gives fairly wide variations even with the monitor held absolutely still.
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I bought a pulse oximeter today
Is it giving consistent readings?
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Is it giving consistent readings?
I've only tried it on myself 3 times in a day, and got a range of 95-98%.
This averages in the recommended range - nothing to worry about!
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I've only tried it on myself 3 times in a day, and got a range of 95-98%.
I was just curious whether it varies between consecutive display updates as you sit and watch it, like mine does.
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I've only tried it on myself 3 times in a day, and got a range of 95-98%.
I was just curious whether it varies between consecutive display updates as you sit and watch it, like mine does.
You might be interested in this https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5539125/
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Taking multiple readings from consecutive display updates gives fairly wide variations even with the monitor held absolutely still.
If nothing else changes, believe the data!
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When I was looking at the pulse oximetry devices available on display, I saw another device which did pulse oximetry, but also claimed to be able to detect atherosclerosis.
- The implication on the box was that it analyzed the pattern of the pulse of blood reaching your finger to determine the stiffness of the arteries between the heart and finger.
- The aorta acts as a shock absorber between the heart and the rest of the circulatory system
- Furring of the arteries in your arm would conceivably change the waveform too.
But because it was almost 4 times the price, I didn't bother with this one.
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I'm convinced that the handheld oximetry is all over the place. Although it can give some information about you if you see major shifts from your "normal".
Mom has been in the hospital a few times for surgery, and regularly plunges down to 90% or so, and often with relatively low BP. Eventually they had to reset all the alarms to lower values, otherwise the alarms would be blasing false negatives all the time.
You forgot the "pulse" part of the pulse-ox.
If you are in respiratory distress, your breathing rate will increase, as well as your pulse. Each person's normal resting pulse will be a little different.
I got pneumonia a couple of years ago (I'm blaming it on stupidly not getting the Swine Flu vaccine, them missing the disease the first time around, but getting it the second or third time it swept around).
My oximetry dropped down into the upper 70's, and my HR stayed around 100-105 BPM for over a week. I was walking, but struggling. Never admitted to the hospital, although I would have been close. I think I actually had broken the fever and was improving by the time friends and family drug me to the clinic. But I still had to cough up the whole lungs.
To a large extent, the oximetry slowly recovered, but the pulse was most representative of my overall condition.
Oh, I tried the pulseox on an acquaintance. Apparently he had a hand cut off and reattached years ago, so his right/left oximetry varied by about 10%. Take it on the wrong hand and it looks like it could be very serious.
I think temperature also impacts the oximetry. I think my hands are comfortable down to about 50°F, perhaps even lower. But, the blood flow may slow down a bit. I'm not convinced the hand is the best place to measure it. In some cases a clinic will measure it on the ear lobe, or perhaps other places.
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Peripheral blood flow is reduced at low temperatures, but 50C is not a low temperature - it is actually the maximum permitted surface temperature for tools and household gadgets, above which the skin can blister and burn.
"Pulse" is the clever bit. The oximeter measures the relative transmissions of red and infrared light at the maximum and minimum intensities of both, thus correcting for the unknown constants such as skin color and thickness and ignoring venous flow which is much less pulsatile.
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I have a pair of oximeters, both the same model, and the difference between them is 1.16%, based on an average of 80 pairs of readings, which is well within tolerance, but the instantaneous difference between any one pair of readings is ±6%, so you might reasonably wonder whether they're of any use at all.
My own SpO2 is all over the shop, varying from 88% to 98%, but usually 93%. If I make an effort to breathe more deeply it will rise to 95%, but if I continue it then falls back to 93%, which rather seems to suggest that there's some sort of homeostasis at work. If I breathe hard enough for long enough it makes me go dizzy, which also suggests that more isn't necessarily better.
Any thoughts?
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I've already been taken to A&E, but my SpO2 was 96-100% then.
Sounds like your pulse oximeters are rubbish. A lot of the ones you can buy aren't properly calibrated. Even the properly calibrated medical ones have a known issue- they're rather less accurate for non white people (which they were mostly calibrated for). If you happen to have darker skin, that can be a significant problem because you may need to go to hospital, but the pulse oximeters may say you don't need it.
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If you are in respiratory distress, your breathing rate will increase
They're currently being publicised because people have been getting dangerously low oxygen levels without any sense of breathlessness.
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Sounds like your pulse oximeters are rubbish.
Mine is the model that the NHS are currently loaning to covid patients, it's specified accuracy is ±2%. I have looked up monitors made by Fukuda Denshi, who make the ones that I've been on in hospital, and they don't specify any accuracy at all.
https://www.england.nhs.uk/coronavirus/wp-content/uploads/sites/52/2020/06/Pulse-Oximeter-Easy-Read-final-online-v4.pdf
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Yes, pulse oximetry is really very helpful & must have product.
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Yes, pulse oximetry is really very helpful & must have product.
Ah yes, but if you try to spam us you will quickly run out of that which keeps you alive here