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PRODUCT REVIEW: Renpho Pulse Oximeter

Renpho Oximeter on top of its instructions. Note the helpful use of square root symbols in the instructions.
Renpho Oximeter on top of its instructions. Note the helpful use of square root symbols in the instructions.

by Andrew Chalk

Do you have a pulse oximeter? I didn’t even know what it was but it is the name for one of those plastic gripper things that they put on your finger at the doctor’s office. I was just sent an offer by Renpho to get one for free by buying it, reviewing it, sending them a copy of the review, and getting a refund. I normally ignore this kind of offer. They are too post hoc, ergo propter hoc. Plus, I forget to apply for the refund. The difference here was that I have a Renpho bathroom scale. It is the best bathroom scale I have ever owned, and not just because it makes me feel lighter. It sends all the measurements to my cell phone, and I can share them with other people. So I can have weight loss races with my sister in Australia. I could even race a kangaroo in Australia (if it stopped hopping up and down on the scale).

What is an Oximeter? Its primary purpose is to measure your blood oxygen level. It gets this by using red and infrared light sources and a light sensor. The value is reported as a percentage named SpO2. For healthy lungs that runs between 95% and 100%. When I stuck my index finger in the Oximeter it measured zero, confirming that I was dead. After putting batteries in the thing I found that finger placement has a major effect on the reading. It started at 94% but with a bit of wiggling it was back up to 100%. Reassuringly quick health improvement. The SpO2 level drops with the degree of respiratory disease, making it more relevant maybe in these COVID-19 laden times. However, if your SpO2 level drops to 88-92 percent do you need a nipper on your finger to tell you that, or are you already gasping for air?

As a freebee, the display also gives you your pulse, which you already got from your Apple Watch, so I will dwell on it less.

It also gives you something called PI%, which is not mentioned in the instructions or present in the display image in the instructions. A carrier pigeon to Renpho’s excellent support revealed that to be the Perfusion Index. Defined thus: ‘The perfusion index (PI) is the ratio of the pulsatile blood flow to the nonpulsatile or static blood in peripheral tissue. Perfusion Index thus represents a noninvasive measure of peripheral perfusion that can be continuously and noninvasively obtained from a pulse oximeter’. Loosely, it is a measure of pulse strength at the measurement site. It varies from 0.02% for a very weak pulse to 20% for an extremely strong one.

Now, those so-called instructions. Have you ever picked up a prescription to find that it had instructions in the box on what looked like scrap paper folded 40 times? Worse still, printed in 4 point type and covering such things as ‘indications’, ‘contraindications’, and dire warnings not to operate a pregnant machine while taking the drug? Well, the same guy wrote these instructions, and he borrowed the same paper. Even the text is cheerfully illiterate. Consider the following word salad:

“2.1 Principle. Principle of oximeter is as follows: An experience formula of data process is established taking use of Lambert-Beer Law according to Spectrum Absorption Characteristic of reductive hemoglobin (Hb) and oxyhemoglobin (HbO2) in glow and near infrared zones”.

So there.

Should you have an oximeter? I think its results are only important in the same sense that it is important for the average male to know the length of his penis against the population average of six inches -- idle curiosity.

In the meantime it is more important to know what features are in the next generation smartphone.

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