The worst effect of sleep apnea is a low level of oxygen in the blood throughout the night (and a bed partner who keeps elbowing you to kick-start your breathing or to shut up your snoring, but that's another issue). Oxygen saturation should never fall below 90%, but in cases of sleep apnea the saturation level can drop below 70%. Over time low oxygen saturation can have a devastating impact on a human body (even more so than those viscious elbows). Sleep apnea isn't always considered a cause of chronic hypoxia - or long term oxygen deprivation - but the fact remains that if left untreated, sleep apnea will deprive a human body of the amount of oxygen necessary for normal, healthy cell function. The end result: daytime sleepiness, sluggishness, and an inability to perform physical and mental tasks. Waking up in the morning and beginning to breathe normally again doesn't make up for eight hours of oxygen deprivation. Everyone who has sleep apnea knows this to be true. The good news for those who suffer from sleep apnea is that CPAP therapy is a very safe and effective treatment that keeps the user's airway open and oxygen levels up throughout the night.

During a polysomnography, two of the many channels of information that are recorded are the pulse rate and the oxygen saturation. This is important information to record during a sleep study because a low level of oxygen in the blood - which often corresponds to an increase in heart rate - can indicate hypopnea or apnea events and can help a doctor diagnose sleep apnea. This information can also be used to show a patient the importance of addressing the sleep disorder.

Pulse oximeters are instruments that can be used by individuals at home to view these two important pieces of information on a regular basis. They're useful for instantaneous spot-checks, and the pulse oximeter models which record data are especially useful for monitoring pulse and oxygen saturation during sleep. Reporting software can be used with the pulse oximeters that have recording capability, so that after a sleep session (whether a nap or an entire night) all the details can be printed out and analyzed.

In this article I'll cover very briefly the history of pulse oximeters, and then I'll focus on the various pulse oximeters we sell while highlighting the CMS 50E model and the software that is included with it.

Really Brief History of Pulse Oximeters
Developments that would eventually lead to modern pulse oximetry began in the early 1930s when German researchers first experimented with light transmission through human skin, presumably with an interest to develop an oxygen meter for pilots. In the early 1940's a British researcher by the name of Millikan produced an oxygen meter for aviators, and he coined the term "oximeter". In the early 1970s, two Japanese engineers working independently further developed a non-invasive method for measuring oxygen saturation using light transmission through translucent tissue. Their efforts were followed shortly by the Biox Corporation in the United States who marketed their pulse oximeters directly to healthcare professionals including anesthesiologists, who before the invention of pulse oximetry had little visibility of oxygen saturation during surgery. Pulse oximeters became widely available to consumers in the 1980s. The most common pulse oximeters still use the 2-wavelength method of light transmission. A big advantage of small fingertip pulse oximeters today is their small size, recording capability and computer connectivity capability. (Eighty years of history sounds so easy, doesn't it?)

The following is a chart showing the pulse oximeters we sell and a brief comparative description for each:

Pulse Oximeter ModelPulse Oximeter Model Description
CMS 50DL Pulse OximeterThe most basic model we sell. Great for spot checks, athletics, climbing, general healthcare. FDA approved. CE marking.
CMS 50D Pulse OximeterThe next step up from the CMS 50DL, the 50D features a color OLED screen. FDA approved. CE marking.
CMS 50D Plus Pulse OximeterFeatures alarm function, USB connectivity to computer, and includes reporting software and USB cable. Uses regular alkaline batteries. FDA approved. CE marking.
CMS 50E Pulse OximeterSimilar to the 50D Plus but with an upgraded display and a rechargeable lithium battery. FDA approved. CE marking.
CMS 50H Pulse OximeterAll the features of the CMS 50E with the capability to record perfusion index (or intensity of pulse). Pending FDA approval.
CMS 50F Pulse OximeterThe only wrist-mounted display unit we sell. Functionally equivalent to the CMS 50E. FDA approved. CE marking.

The 50D Plus, 50E, 50H and 50F are the four models with recording capability. If you're interested in using a pulse oximeter when you sleep with your CPAP machine then you should select one of these models. The 50DL and the 50D do not record, so they're more suitable for instantaneous spot-checks rather than for prolonged use. Note, too, that although the recording models can record for up to 24 hours, each time you start a recording session the previous data will be erased. So, it's important to download your data after each session before you start another session.

Setting Up the CMS 50E Pulse Oximeter
The first step in using the CMS 50E is charging the battery. Using the included AC wall adapter/USB cable as the power cord, charging only took about two hours. A light on the oximeter indicates charging is taking place, and when the light goes out the charge is complete. To turn the pulse oximeter on you just press the button for a second and wait for the display to light up. If you haven't already inserted your finger into the oximeter the display will show a "Finger Out" message. If you don't insert your finger within about five seconds the unit will shut down. If you insert your finger (or if you already had your finger inserted when you turned on the oximeter) then the screen will show your pulse rate and oxygen saturation level within a few seconds.

CMS 50E Pulse Oximeter
The CMS 50E Pulse Oximeter 'Finger Out' Message

Once the pulse oximeter is on and working, you really don't have to do anything at all. Just look at the screen and you'll see your pulse rate and oxygen saturation percentage. The display shows the following:

Alarm Indication: A symbol of a bell. A red X through the bell indicates the alarm is turned off.
Pulse Sound Indication: A symbol of a speaker. A red X near the speaker indicates the pulse sound is turned off.
Battery Capacity Indication: A symbol of a battery. Full green means the battery is full.
Pulse Rate: A 2- or 3-digit display showing the pulse rate.
Pulse Bar Graph: An animated bar graph to the right of the pulse rate that moves with each pulse.
Pulse Waveform: An animated waveform graph at the bottom of the display that represents the pulse rate and pulse intensity.
SpO2 Low Alarm Indication: A number to the lower left of the SpO2 number which indicates the SpO2 level below which the alarm will sound if the alarm function is turned on.
SpO2: A number to the left of the pulse rate which shows the saturation of peripheral oxygen in the blood.

CMS 50E Pulse Oximeter
The CMS 50E Pulse Oximeter In Use at Lowest Brightness Setting (This Thing is Bright!)

The main button on the front panel of the pulse oximeter is used for a few different things:

  1. press to turn the unit on
  2. press when the unit is on to go to the settings menu
  3. click to navigate from one menu setting to another
  4. press to change a setting in the menu

A click is a short press of the button, and a press is a prolonged push of the button.

Recording and Uploading Data Using the CMS 50E Pulse Oximeter
To record data, press the button until the settings menu appears. Then click the button until Record is highlighted. Press the button with Record highlighted, then set the current time by clicking to the appropriate hours/minutes field and pressing the button to adjust that field. Then click the button to underline the Y and press the button to exit the time setting menu. It's much easier to do it than to write how to do it, so just figure it out on your own if this all sounds like nonsense.

CMS 50E Pulse Oximeter
The CMS 50E Pulse Oximeter Settings Menu with Record Function Highlighted

When I first setup the pulse oximeter for recording I thought I was entering the duration of the recording, not the current time. So I set the time to 01:00 thinking that meant it would record for an hour then stop. When it didn't stop recording after an hour I figured out you have to stop recording manually, and that I had set the time incorrectly on the device. The only negative effect of this was that the reports show that my recording session occurred from 1:00 AM to 2:30 AM when in fact the session occurred from about 11:00 PM to 12:30 AM.

While recording there's an REC indicator and a flashing red dot on the screen. After a few seconds the display goes into power saving mode. If you click the button the display will show a message that simply says "recording", and then the display goes dark again. If you press the power button while recording and in power save mode, the screen will turn on like normal. Then you can press the button again to go to the settings menu to manually stop recording.

Once you've stopped recording you'll want to upload your data to your computer. Here are the steps for uploading.

  1. First, be sure to install the software that was included with the pulse oximeter.
  2. Then hook up your pulse oximeter to your computer with the included USB cable.
  3. After installing the software launch the SpO2 Review application. Your pulse oximeter device will show up in the connection field of the software.
  4. Click on New Session, enter your name (which will be part of the saved file name) and click OK
  5. Turn on the pulse oximeter, go the settings menu and turn on the Upload setting

Pulse Oximeter Software

After about ten seconds all the data will be uploaded and you'll see two graphs on your screen.

Pulse Oximeter Software

There's a printer icon in the lower right corner of the SpO2 Review application window. Clicking on it will give you the option to print four different reports: summary, full study, oximetry, strip chart. The summary report and oximetry report contain the most detailed information so I'll highlight those here:

Summary Report
The summary chart is good because it includes summary data in columnar form so that you can easily see your average SpO2, your average pulse rate, desaturation events, pulse events, and more.

Pulse Oximeter Software

Oximetry Report
The oximetry report is very similar to the summary report but adds detail regarding the SpO2 (oxygen saturation) measurments. For example, on the oximetry report you'll see a table that shows SpO2 events, a table that shows time at different saturation levels, and two charts that correspond to each of these tables.

Pulse Oximeter Software

Saving Data
A file will be saved automatically on your computer, so that the next time you start the software you can open the file. You don't have to re-upload the data from the pulse oximeter.

Viewing The Pulse Oximeter Data On-Screen in Real Time
When you installed the software earlier, you installed two applications. The SpO2 Review software is for generating reports from saved data. The other application is called SpO2 and allows you to view real-time data on your computer screen. The practical application of this software is somewhat limited for most people if you're connecting the pulse oximeter to the computer with a USB cable. However, in the event you're caring for someone else and you want to monitor their pulse and oxygen information and you want to be able to see the information on a big computer screen rather than the small fingertip screen, this might be quite useful. You could use this software to monitor yourself in a similar fashion. Of course, it's very nice for the visually impaired who might find the small fingertip screen difficult to read. Here's a screen shot:

Pulse Oximeter Software

Managing Your Health
Any pulse oximeter can be used to effectively manage your health. They're handy to have for everyday exercising (I use one when I walk or run on a treadmill). The alarm feature found on many models, including on the CMS 50E, can signal you to an oxygen or pulse event of which you might not otherwise be aware. For example, with an alarm-enabled pulse oximeter you could set a high pulse rate of 90 and a low SpO2 percentage of 85 so that when you sleep with the oximeter you'll be awakened if your pulse skyrockets or if your oxygen saturation plummets. This type of alarm could make you aware that you've removed your CPAP mask during the night, or that your CPAP machine stopped working during the night. If you're a pilot in a small, non-pressurized aircraft and you're flying above 10,000 feet then an alarm like this can literally save your life. If you have a condition other than sleep apnea that results in chronic hypoxia, and if you're on oxygen for that condition, then a pulse oximeter is a really good device to have.

If you have any questions about any of the pulse oximeters on our website, feel free to contact us. We'd be happy to help you!

Andrew Senske
President is a leading online retailer of CPAP equipment. Located in Spokane, WA has been serving thousands of customers around the world since 2001. Founded on a belief that patients are their own best primary care providers, understands the importance of educating patients and customers on both the effects of and treatment for obstructive sleep apnea. For more information visit or call toll free 1-888-955-2727.

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