If you’ve had an exam, a doctor may have clipped a device to your finger to measure your oxygen saturation (SpO2) and heart rate. Up until last year, that was my only experience with such devices, but during the pandemic, I and many others have purchased our own pulse oximeters to check at home for possible signs of COVID 19 or otherwise
breathing problems. They’re available online for just $15, but, as the FDA warns, “Although pulse oximetry is useful for estimating blood oxygen levels, pulse oximeters have limitations and, in certain circumstances, a risk of inaccuracy that should be considered.” The agency cautions pointed out several factors that can affect the accuracy of a pulse oximeter reading, “such as poor circulation, skin pigmentation, skin thickness, skin temperature, recent tobacco use, and use of nail polish.” A study of six inexpensive pulse oximeters, as reported in the journal Anesthesia & Analgesia, found that “many inexpensive pulse oximeters sold to consumers have grossly inaccurate readings.”
I bought the Zacurate 500BL Fingertip Pulse Oximeter from Amazon for $15 and brought it to a doctor’s appointment. The doctor’s medical oximeter showed my SpO2 at 100 while the home unit showed 97. The SPo2 values can change from minute to minute or even from second to second. So if I had done this comparison at a different time, I might have gotten different results.
levels while sleeping
Most clip-on monitors only show you your real-time SpO2 reading, which of course means you have to be awake to read the screen. But there are some that have memory and a Bluetooth connection to a smartphone so you can track your SpO2 over time, even while you sleep. Some fitness bands and smartwatches also measure SpO2, including some of the higher-end Fitbit models and the Apple Watch Series 6.
I generally wear a Fitbit Sense ($200) to bed, and for the past week I’ve been testing the O2 Ring ($165 at GetWellue.com), one of the most popular oxygen saturation and heart rate monitors designed to be worn while you sleep. Wellue promotes the product for people struggling with snoring, sleep apnea, COPD, pneumonia and asthma, and for pilots who can develop hypoxia at altitude. But, as I will detail below, consult a doctor before relying on any device.
The Fitbit gives you an average SpO2 for your night and a range of the highest and lowest readings. The watch itself shows your real-time heart rate, and the Fitbit app shows a graph of your heart rate over a 24-hour period. Fitbit only reports overnight SpO2 readings.
The O2 ring provides much more granular data. In addition to the average, high, and low for the night, the companion iOS and Android app shows how often it has fallen 4% or more below your baseline, as well as the number of drops per hour. There is also a graph of your SpO2, pulse and movement during the night or whenever you wear it. You can download this report as a PDF to read, print, or email to your doctor. If you want highly granular data, you can download a table that shows your SpO2 and pulse rate in 4-second intervals. So if you notice a drop in the graph, you can use the table to see exactly when it happened, how long it lasted, and what your rate was seconds before or after the drop. The device also lets you set alarms so that it vibrates when your SpO2 falls below the level you set (between 80% and 95%) or when your pulse rate falls above or below a certain level. The vibration will likely wake you up, which may or may not be a good thing. Lookee, which sells the O2 ring, says on its website that a vibration “indicates you need to change your sleeping position to improve breathing,” but I can’t verify the accuracy of that statement.
Too much information
I get some useful information from the O2 Ring, but when it comes to a device that measures fitness or health, I sometimes wonder if there is such a thing as TMI (too much information). I feel the same way about online health searches. Times are stressful enough these days and we have to think about how much information we want to process and worry about and of course whether that information is correct and understood in context.
I emailed Scott Kutscher, an associate clinical professor of psychiatry and behavioral sciences who is a practicing sleep medicine doctor at Stanford Sleep Medicine Center. Kutscher said that “home oxygen monitoring can be a useful screening tool if you suspect a sleep disorder like sleep apnea. It can also be helpful to monitor treatment progress,” but cautioned that such monitors “are not used to diagnose problems.” So if you think they show something is wrong, you should consult a doctor or other trained professional.” According to TMI, he said, “Data can lead to incorrect assumptions or conclusions. When I ask patients how they sleep, they sometimes reply, “Well, my watch says…” but your watch can’t tell you how you slept.”
Searching for health data can sometimes be counterproductive. “In sleep medicine,” Kutchner added, “we have a term orthosomnia that refers to poor sleep caused by the pursuit of perfect sleep.” In fact, an article in the Journal of Sleep Medicine based on three case studies suggests that “Sleep trackers can present unique challenges… and increase sleep-related anxiety or perfectionism in some patients.
I’m not a doctor, but I do have a PhD in Education. And one thing most educators know is that you need to get your information from reliable sources. If you suspect you have a sleep disorder or other medical condition, seek your advice from a qualified medical professional, not a device or technology columnist.
Larry Magid is a technology journalist and internet safety activist.