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How Pulse Oximeters Work (2015)

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Re: How Pulse Oximeters Work (2015)

#31

Post by DangerousPie »

mturmon wrote: post #22
DangerousPie wrote: post #17

Does anybody have any suggestions for how to check whether a pulse oximeter actually works properly? I bought one online from a not particularly trustworthy shop. I have never seen it show any value other than 99%. How can I figure out whether it actually does anything and doesn't just show 99% no matter what?

I purchased a relatively cheap one from Amazon a couple of months ago. Less than $50, I believe. I tried some simple stuff when it arrived. I believe I was able to get it to swing within the 94-99% range by holding my breath and by deliberate, deep breathing, over the span of just a minute or two. It definitely was not pegged at 99%. The changes were surprisingly fast. My wife was able to get the same response. If it…

How long did you hold your breath for?

Re: How Pulse Oximeters Work (2015)

#32

Post by alkonaut »

asveikau wrote: post #29
popotamonga wrote: post #5

Earlier quoted context omitted.

I discovered i have a problem with one. Every one else who tried it had 98-100 all the time. I had < 94 no mater what

I thought I recall reading that 94 is not dangerous or abnormal, and 90 is when you should get checked out.

This is something that is still not quite understood by doctors.

I take my kid (Who has a respiratory condition) to hospital at 90.

In my experience if you are in hospital with oxygen because of a respiratory illness, the oxygen would probably be given once you dip below 92-93 assuming they know you have a respiratory condition. Not because that’s the danger level but because they want to be able to tweak the O2 if you fall even lower. Doctors then usually instruct nurses to adjust the flow so saturation stays in the 90-95 range.

People at high altitude or in airplane cabins can be at 70% for hours without even noticing. Meanwhile someone having a dip from 90 to 80 with pneumonia might be gasping for air.

Re: How Pulse Oximeters Work (2015)

#33

Post by amiga_500 »

Does anyone know the degradation in blood oxygen levels under moderate exercise for a person who is fairly health (not athlete but slim, does regular exercise)?

I had covid, so bought one of these, and I'm now building my way back to being able to jog, after months of shortness of breath. I would like to be able to understand what level my blood oxygen %, for a normal, healthy person, would drop to when say jogging.

Re: How Pulse Oximeters Work (2015)

#34

Post by brucen »

pizza wrote: post #25
monty5811 wrote: post #6

Earlier quoted context omitted.

Pulse oximeters are not all that simple. The general idea is easy enough to get across and it's possible to build a fairly simple one that will work some of the time. But the top end, highly reliable ones that work well at low sats are pretty complicated things.

Interesting. You're probably not the right person to ask about this sort of thing and I should probably stick with a doctor's opinion, but you may have a better intuition than I do about the reliability of these things' readings. Suppose I use a pulse oximeter and I get readings of 90%, 91%, 92%, and 99%, all taken ~one minute apart. Is it most likely that I am fine and there were some issues either with the hardware…

It often takes a while for the probes to stablise and get an accurate reading, so this is a very common pattern, but I haven't looked into why. I think part of it may be the machine calibrating to the flow of blood through the area of skin you have chosen. You often apply the probe and sit it there for 30-60s waiting for it to stabilise.

If you are worried, ask them to leave it on throughout your consult. You should see it sit at 99-100% for the rest of your stay.

Re: How Pulse Oximeters Work (2015)

#35

Post by VectorLock »

deadmutex wrote: post #23
wlesieutre wrote: post #18

Speculated to be included in the Apple Watch S6 this fall. https://9to5mac.com/2020/03/08/apple-watch-blood-oxygen-satu... At the time they reported that there were mentions of it in an iOS 14 leak, but it wasn't clear if it would be a software update to existing watches (somehow able to detect it with existing heartrate hardware) or in a watch hardware revision. Since it wasn't mentioned in the watchOS news at WWDC,…

IIRC, Fitbit has products on the market that has them. Works both on iOS and Android. https://www.wearable-technologies.com/2020/01/fitbit-adds-bl...

Wow they finally did it. After the hardware being there for _years_ they managed to get around to enabling the software. I already jettisoned them for Garmin after waiting so long.

Re: How Pulse Oximeters Work (2015)

#36

Post by VectorLock »

DangerousPie wrote: post #17

Does anybody have any suggestions for how to check whether a pulse oximeter actually works properly? I bought one online from a not particularly trustworthy shop. I have never seen it show any value other than 99%. How can I figure out whether it actually does anything and doesn't just show 99% no matter what?

Hold your breath. I've done that with a fingertip pulse oximeter I have.

Re: How Pulse Oximeters Work (2015)

#37

Post by supernova87a »

wlesieutre wrote: post #18

Speculated to be included in the Apple Watch S6 this fall. https://9to5mac.com/2020/03/08/apple-watch-blood-oxygen-satu... At the time they reported that there were mentions of it in an iOS 14 leak, but it wasn't clear if it would be a software update to existing watches (somehow able to detect it with existing heartrate hardware) or in a watch hardware revision. Since it wasn't mentioned in the watchOS news at WWDC,…

Does anyone know, in general, if a watch device already has a pulse measurement LED system, whether that can also serve as a pulse ox measurement? or are they different hardware requirements?

Re: How Pulse Oximeters Work (2015)

#38

Post by oehtXRwMkIs »

Fun fact about pulse oximeters: in California EMTs are regulated so strictly that it is illegal for them to use a pulse oximeter as it is deemed "invasive". So if anyone is experiencing a medical emergency that could successfully be delayed following the algorithm involving checking blood O2, they better hope the EMT is experienced/lucky enough to suspect low O2 or that there's a paramedic or nurse on board. It's definitely one of those laws that aren't really enforced but it's weird that in California EMTs have to break the law to do basic screening.

Re: How Pulse Oximeters Work (2015)

#39

Post by alister »

dmitrygr wrote: post #27

It is really grating that all the visualizations are wrong. Blue is shorter wavelength than red. Infrared is longer wavelength than red. Every single image is wrong. :(

The author explains his visualization as follows:

One is a red light, which has a wavelength of approximately 650 nm. The other is an infrared light, which has a wavelength of 950 nm. (Throughout our description, we will show the infrared light in light blue. In reality, infrared light is invisible to the human eye.)

Re: How Pulse Oximeters Work (2015)

#40

Post by hakcermani »

dmitrygr wrote: post #27

It is really grating that all the visualizations are wrong. Blue is shorter wavelength than red. Infrared is longer wavelength than red. Every single image is wrong. :(

The blue color is being used for infrared so the wavelength is right. The author could have used a '-- red' for infrared rather than blue to be less confusing.
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