Daily App: digiDoc Pulse Oximeter tries to measure your heart rate and oxygen levels

digiDoc Pulse Oximeter is an iPhone app that uses your camera to measure your heart rate and your oxygen level. Apps that measure your heart rate are a dime a dozen, but this is one that combines heart rate with blood oxygen saturation.

Like most heart rate apps, digiDoc Pulse Oximeter requires you to place your finger over your camera and lens and wait a few seconds while the app takes its measurements. With the digiDoc Pulse Oximeter, there is an extra calibration step in the beginning that turns on the LED flash and adjusts the app before you place your finger on your phone. The app walks you through the calibration and measurement using on-screen prompts, making it easy to use. In a minute or so, the app will report that it is finished and will show your heart rate and SpO2 measurement. A useful running log keeps track of all your measurements in the app.

digiDoc Pulse Oximeter has a beautiful, easy-to-use design that fits in well with iOS 7, but its reliability in measuring SpO2 is questionable. I compared digiDoc Pulse Oximeter against a portable pulse oximeter, and the results varied widely. For evaluation purposes, I used the app on myself while sitting and while exercising at near maximum. I also tested a family member who was being treated for pneumonia.

In my testing, I found the app to be accurate when SpO2 levels were high, but variable when SpO2 levels started to drop. The app never accurately measured my family member, whose SpO2 levels were in the low 90s. The app showed a decrease in his SpO2 levels by measuring it at 96 percent, but it never registered as low as 92 percent, which is what the hospital and home pulse oximeter were registering. When you're talking about pulse oximetry, there is a big difference between those two or three percentage points.

I also noticed variability in readings when exercising, but for a different reason. The digiDoc Pulse Oximeter was widely inaccurate while exercising because it is hard to keep moving vigorously and keep your hand on the camera of your iPhone. It's difficult, if not impossible, to keep your finger and the phone steady while you run or bike. You can take measurements when you stop, but that defeats the purpose of using oxygen levels to measure your exercise intensity.

Overall, digiDoc Pulse Oximeter is a useful app for measuring heart rate. Heart rate measurements were spot on with the portable pulse oximeter, even when exercising. The SpO2 measurements, however, were variable and not reliable enough for me to recommend using it for other than novelty. If you have a medical condition that requires SpO2 measurements, you are better off buying a $50 portable unit from a drug store or medical supply company.

digiDoc Pulse Oximeter is available from the iOS App Store for US$3.99. It requires iOS 7.