freshd

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/articleDetail.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