Pulse Oximetry explained

A Pulse Oximeter (PulseOx) is a useful tool, but exactly how does one work? Obviously, it’s not magic, though it might as well be. Very few people can tell you what happens in the couple of seconds that occur after you place it on your finger.

Pulse Oximeters were invented in the 1940’s by scientist Glen Milliken, who published his ideas in a research paper titled The oximeter: an instrument for measuring continuously oxygen-saturation of arterial blood in man. But it looked nothing like the Oximeters we have today: those wouldn’t appear until the Japanese refined the technology in 1972.

But the average person still wouldn’t have been able to purchase a Pulse Oximeter. Biox made it into a commercial product in 1981, and it was the late 1980’s before they really began to catch on in the United States.

So how do they work? A Pulse Oximeter emits light from two different sources: a red light that you can see, and an infrared light that you can’t see. As the PulseOx is placed on your finger or ear the lights activate automatically.

The red light (which has a wavelength of 660 nm) shines through the finger and is absorbed by hemoglobin. The problem is, everything else in the body absorbs light, also. So the infrared light is used too – it has a higher wavelength and is absorbed at a different rate than the red light. A receiver picks up the light waves from both sources as they leave the body, and the Oximeter’s computer chip compares the two. The comparison values are entered into a mathematical formula (CLICK HERE and page down to see the formula that makes Pulse Oximetery possible) and the answer is displayed on the screen – all in a matter of moments!

If I had to do the math to figure out the Oxygenation level, It would take all day to get one reading!

Oximetery does have its limitations: while most people think it is a beat to beat accurate measurement, it is not. It is an average over time. Another big drawback is that it can be fooled by Carbon Monoxide poisoning. hemoglobin mated with Carbon Monoxide responds like oxygen mated Hemoglobin, so a patient dying of Carbon Monoxide poisoning will give a PulseOx reading of 90% or higher.  Also, dark skin could cause inaccurate readings. This 2007 report contends that it does; later reports either report no effect or draw inconclusive results.

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3 Responses to “Pulse Oximetry explained”

  1. carolyn compton Says:

    When I was in hospital having my boys, three years ago, I lent some nail polish remover to a new-to-be mum having an in-utero operation on her child. Her family had shouted her a lovely manicure the day before! Poor mum had to remove lovely nail polish because of pulse oximetry “)

  2. Finger Pulse Oximeters Says:

    Not only nail polish but I have seen dark pigmentation get in the way of readings as well.

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