oxygen meters

[RichD]

Anybody know anything about the innards of those fingertip
O2 rate meters? sensor, theory of operation, silicon, etc.?

I recently had some medical treatment, they were checking it
3 times / day, and I'm curious -

I don't expect chemists to be experts on the electronics,
but maybe the chemistry -

--
Rich

[Andy Burns]

RichD wrote:

> Anybody know anything about the innards of those fingertip
> O2 rate meters? sensor, theory of operation

Shine a red light and an infrared light through* a blood vessel onto an
opto sensor.

check the relative absorption of the two wavelengths in the blood, there
is a correlation between oxygen saturation and their absorption ratio.




[*] not reflected off the blood vessels like the phone versions.

[dlzc]

On Tuesday, February 16, 2021 at 5:02:47 PM UTC-7, Andy Burns wrote:
> RichD wrote:
>
> > Anybody know anything about the innards of those fingertip
> > O2 rate meters? sensor, theory of operation
> Shine a red light and an infrared light through* a blood vessel onto an
> opto sensor.
>
> check the relative absorption of the two wavelengths in the blood, there
> is a correlation between oxygen saturation and their absorption ratio.

And they can be fooled by CO in the blood too.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7301832/
... just as we can produce acid in our muscles under stress, we can produce CO as well as part of an abnormal respiration...

David A. Smith

[RonTheGuy]

On Feb 16, 2021, Andy Burns wrote
(in article<news:i934p3...@mid.individual.net>):

> Shine a red light and an infrared light through* a blood vessel onto an
> opto sensor.
>
> check the relative absorption of the two wavelengths in the blood, there
> is a correlation between oxygen saturation and their absorption ratio.

Why red?
TIA

Ron, the humblest guy in town.

[dlzc]

Dear RonTheGuy:

On Thursday, April 1, 2021 at 11:22:44 PM UTC-7, RonTheGuy wrote:
> On Feb 16, 2021, Andy Burns wrote

> > Shine a red light and an infrared light through* a blood
>> vessel onto an opto sensor.
>

> Why red?

Most efficient.
1) Red LEDs are very efficient and low voltage,
2) If you put a "white light" flashlight up against the palm of your hand the only light that makes it through is red, and
3) Red blood cells change color based on the amount of oxygen (or carbon monoxide) they contain.

Ride the horse in the direction it is going.

David A. Smith

[Härra Ramob]

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[Info Libera]

Maybe tha the red light penetrates deeper than blue light.
The reason is that skin consists of a range of chromophores which have scattering and absorption coefficients which are highly wavelength dependent ...
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5653719/