“I noticed that the sleep analysis on the web app now includes “Respiratory Rate,” how is that measured and what does it mean?”
WHOOP measures Respiratory Rate while you sleep and reports it in units of “breaths per minute.” The number you see in the sleep statistics box is the median number of breaths per minute throughout the night. Typical values range from 12 to 20 breaths per minute. We calculate Respiratory Rate from the raw heart rate data by taking advantage of a phenomenon known as Respiratory Sinus Arrhythmia. Described simply, when we breathe in our heart rate increases and when we breathe out our heart rate decreases, allowing us to preferentially pass blood by the lungs while they are full of oxygen.
The graph below shows the distribution of all the Respiratory Rates recorded over a recent one-week span among WHOOP users.
WHOOP has actually been tracking Respiratory Rate throughout sleeps for a long time now. We use minute-by-minute changes in Respiratory Rate in our sleep staging algorithm because Respiratory Rate predictably changes during different sleep stages. In the past, WHOOP didn’t store or display median Respiratory Rate because it generally follows a similar trend as HRV and RHR, so we weren’t sure how our users would action this information.
However, in an effort to always improve the analysis and recommendations we provide, we discovered something interesting: While it is true that Respiratory Rate is generally an indicator of cardiovascular fitness and load and therefore increases when resting heart rate increases and decreases when resting heart rate decreases, it is also a remarkably stable metric. From night to night, users should not expect to see much change in their respiratory rate statistic, but when it does change, that change tends to be meaningful.
For this reason, Respiratory Rate is a useful metric because it makes it easy to spot sleeps in which “something was up.” On the other hand, Resting Heart Rate can meaninglessly change a few beats per minute from day to day. In statistics, this property is known as the “signal to noise ratio,” and it determines how much change you need to confidently conclude that a change is meaningful versus random variation. Median respiratory rate has remarkably high signal to noise ratio, making it very easy to interpret and trust.
In my own data, for example, over the past 30 days my sleeping respiratory rate ranged from 14-15 breaths per minute every night except one--when I was sleeping in a middle seat on a red-eye plane from Boston to Reykjavik. My Respiratory Rate was 17 that night, and I slept terribly.
“Ask WHOOP” is a new concept we’re trying out on The Locker. From time to time we’ll answer questions from our members regarding the various features and analysis WHOOP provides, how to better understand the data, and general tips and tricks for optimizing performance and making the most of your experience on WHOOP.
Have a question you’d like to submit for us to answer in an upcoming post? Email TheLocker@whoop.com with "Ask WHOOP" in the subject line.