The Waveform (or the Squiggly Line on Your Pulse Oximeter)

If it weren’t for high flying aircraft, the oximeter might have taken many more years to be invented. Credit for the very first oximeter is given to Karl Matthes, a German scientist who was studying the effects of low blood oxygen levels in pilots at very high altitudes in 1935. His oximeter was a bit crude, and difficult to use, but it did work using the same principle all oximeters are based on today.

It wasn’t until 1964 that Hewlett Packard introduced the first commercialized ear oximeter – massive by today’s standards. It required a great deal of calibration and upkeep and was very expensive. The first Hewlett Packard oximeter required its own cart to move around and cost $10,000 (or $75,327 in today’s dollars).

digital pulse oximeterIn 1995 the Nonin company introduced the first true digital pulse oximeter. Many companies developed their own line of pulse oximeters resulting in lower pricing and a better product for displaying valuable readings. So it may seem that small, affordable oximeters were always available, but the reality is they have only been around for the past 20 years or so.

We normally focus on the readouts of oxygen saturation and heart rate or pulse. Your oximeter may also display information regarding the effect of your blood as it moves through your circulation with each beat of your heart – we call it the “waveform.” The waveform is an overall reflection of the volume of blood that is circulating with each beat of your heart.

The waveform gives moment by moment information allowing detection of an irregular heart rhythm. This is not an EKG tracing and has nothing to do with the electrical system of the heart. The waveform also shows the strength of the signal itself. A weak signal might cause inaccurate readings of saturation. This may be caused by a decrease in blood flow through the finger (called low perfusion), improper position of the oximeter on the finger or, it even can be due to dirty sensors or LED lights.

It is the shape of the waveform that is easiest to see virtually every time you are checking your oxygen saturation. The shape of a normal waveform is most commonly described as “saw tooth.”

If you see a saw tooth pattern, whose amplitude takes up at least half of the display area, you are probably getting the most accurate readouts of saturation and heart rate. A number of oximeters will show dashes or simply not display any numbers until it “recognizes” a normal waveform configuration. The waveform is an important feature of  more advanced oximeters which is one of  the best investments you are ever likely to make.

John R. Goodman, RRT FAARC

John R. Goodman, RRT FAARC is Executive Vice President of Technical  / Professional Services at Transtracheal Ser­vices, Denver, CO, who says “All You Need Is Love!”