How does an O2 sat monitor work?

Hiya, first post - sorry if i'm a little vague, as I'm don't fully comprehend how these things work myself (not a physicist).
So, from what I gather, the LED (light emitting diode) in the finger thingy (the technical term) sends out 2 wavelengths of red light (which you saw already). The light travels through the finger, appendage, or whatever and reflects against the RBCs and the hemoglobin they contain (carrying oxygen or not), and out to the other side where the sensor on the other side of the probe sends the data to the computer. Using (apparently) well-established algorithms, we're able to extrapolate the percentage of oxygenated blood at the measurement site.
Incidentally, here's an interesting article about the benefits and shortfalls of using pulse oximetry:
http://www.rnweb.com/rnweb/article/a....jsp?id=107354
If you have one molecule of hemoglobin that's fully oxygenated travelling around in your body, your SpO2 is 100% - but obviously not perfusing adequately!
I've heard anecdotally that this technolgy was invented by someone at Stanford in the 90's - there are some interesting research articles on it's use on animals over on PubMed.
All the best and keep asking questions!
dave

The pulse oximeter is actually a computerized gizmo that gives you a ratio of the saturated hemoglobin compared to the unsaturated hemoglobin that it detects expressed as a percentage. It actually emits two different lights, a plain old red light and an infrared light which noninvasively pass through tissue. A sensor which is opposite the two light sources is able to compute the amount of light that is passing through tissue. One of the lights is absorbed by hemoglobin molecules and the other is not. The results of what the light sensor detects from the two different lights is what forms the ratio of saturated to unsaturated hemoglobin that is then mathematically expressed as a percentage.

The aparatus must be able to detect a pulse that is strong enough to bring enough blood flow into the area so the little light is going to be able to bounce off an adequate number of hemoglobin molecules so the ratio can be computed. The pulse must be rhythmic. Pulse ox doesn't work very well in people who have very irregular heart beats.

Wow, good question. Very good answers too! You guys are SO smart!!

as a side note they can also give one a false sense of security in a patients condition. the bigest example is a pt with carbon monoxide poisoning. the will and can read 100% saturation. the pulse ox cant tell the difference between o2 and co. although is did just see the other day that they now have a pulse oximeter that can.

http://www.masimo.com/

rj
:uhoh21:

The best answer I've found on the internet is a pdf at this address:
http://www.maxtecinc.com/docs/pulsox...seOximetry.pdf

Although this thread is 8 years old.......it is good to re-visit some information as it always valuable. Thanks!