Pulse Oximeter

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A Pulse Oximeter is a device for checking how much oxygen is in your blood (Blood Oxygen Saturation or SpO2). They work by shining two different colored lights through your finger and seeing how much of each color is absorbed. A healthy person at sea level should have a SpO2 of 96-99%. A pulse oximeter is primarily used in Altitude Training or when traveling to altitude, but it is also handy for measuring Resting Heart Rate. I recommend two Pulse Oximeters – the cheap ($30) Octive Tech CEN and the more expensive CMS-60C.

1 Getting an Accurate Reading

Because a Pulse Oximeter is indirectly measuring SpO2 via the light traveling through your skin, there are a number of factors that can impact the accuracy of the reading.

  • Fingernail polish. Any polish or covering over the fingernail can create problems for the Pulse Oximeter. If you can use a finger that is clear, that is ideal, but you can twist the Pulse Oximeter sideways to get a reading across the finger rather than down through the nail.
  • Skin color. Dark skin pigmentation can result in an over-estimated SpO2 reading when it the levels are below 80%. Try to find an area of lighter skin color if possible.
  • Movement. Any movement tends to disrupt the measurement, so stay as still as possible.
  • Bright lights. A good Pulse Oximeter will tend to shield out any external light, but try to keep light levels reasonably low and avoid shining a light onto the Pulse Oximeter.
  • Carbon monoxide poisoning. The pulse Oximeter will show the overall saturation of the blood, without telling the difference between oxygen and carbon monoxide.
  • Blood insufficiency. Low blood volume, anemia or poor circulation can all cause problems with the reading.

2 Positioning the Oximeter

These pulse oximeters can be positioned on the finger or the toe. While the toe is the most accurate location[1] there is a delay in the reading[2] that makes it unsuitable for Intermittent Hypoxic Exposure.

3 Recommended Pulse Oximeters

3.1 Octive Tech CEN

This is one of the cheapest pulse oximeters I found, and provides the basic functions adequately. It will display current SpO2 and Heart Rate, and is easy to use. It doesn't have the more advanced features of the CMS-60C or CMS-50E, such as values overnight or interfacing to a computer. I use a similar pulse oximeter to record my Resting Heart Rate each morning.

Fingertip Oximeter Entry Level Octive Tech CEN

3.2 CMS-60C

This is a significantly more expensive and more sophisticated pulse oximeter. Unlike most pulse oximeters the main unit and the fingertip sensor are separate. I find this makes it much easier to use for Altitude Training as there is little weight on the fingertip. Like cheaper pulse oximeters, the CMS-60C will display current SpO2 and Heart Rate, but it will also record the values for up to 24 hours. However, the biggest advantage of the CMS-60C is that it will interface to a computer. I have written some custom software, the Hypoxic Timer, that helps record and evaluate Intermittent Hypoxic Exposure training. The CMS-60C sensor is also easily replaceable, which is nice.

Palm Size CMS-60C Pulse Oximeter with software and probe for Sleep Study

3.3 CMS-50E

Before I got the CMS-60C I used the CMS-50E with my Hypoxic Timer software. I upgraded to the CMS-60C for convenience and the price is not radically different, so I would not recommend the CMS-50E unless you particularly want the compact form factor. Note that this is the only pulse oximeter other than the CMS-60C that I know will work with my Hypoxic Timer software.

CMS-50E OLED Fingertip Pulse Oximeter

4 References

  1. NareshKumar Aggarwal, Jyotirmoy Das, Amit Aggarwal, Pulse oximeter accuracy and precision at five different sensor locations in infants and children with cyanotic heart disease, Indian Journal of Anaesthesia, volume 54, issue 6, 2010, pages 531, ISSN 0019-5049, doi 10.4103/0019-5049.72642
  2. EA. Hamber, PL. Bailey, SW. James, DT. Wells, JK. Lu, NL. Pace, Delays in the detection of hypoxemia due to site of pulse oximetry probe placement., J Clin Anesth, volume 11, issue 2, pages 113-8, Mar 1999, PMID 10386281