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The Pulse of the Nation

The most important vital signal in our analysis is the resting heart rate. Since an increased heart rate could be a possible indicator for fever, which alone is a core symptom of COVID-19, the resting heart rate marks the basis for this study. More on this topic can be found here.

Each day, every connected device delivers information about a donor’s resting heart rate. By collecting this information for a number of days, we can establish a baseline resting heart rate for each donor. Because these values vary under normal conditions, we calculate this reference baseline on an individual-basis. This way, as we receive more and more data, we will be able to detect sytematic deviations from a normal resting heart rate that is unique to each person.

The distribution of the average resting heart rate

Because resting heart rate is our reference point, we need to better understand how this value varies amongst our donors. In short, what is “normal”?

The figure below depicts the distribution of the average resting heart rate over all donors. It shows that values vary roughly between 40 and 90 beats per minute.

Nation-wide average resting heart rate: The daily average resting heart rate is determined for each donor. This baseline follows a nicely shaped Gaussian distribution with values between approximately 40 and 90 beats per minute.

Using this, we can further determine the average resting heart rate over all donors:

Nation wide average heartrate: 60,94 beats per minute

However, one must take into account that the community of donors is not representative of the entire nation.

Temporal stability of the baseline

Naturally, people behave differently in different situations, i.e. on weekdays or weekends or holidays, which has a natural effect on their heart rate. This effect shall be taken into consideration when analyzing the above described baseline. The figure below describes the nation-wide average heart rate as a function of time

Average resting heart rate as a function of time: The nation-wide baseline, aggregated over all donors, is represented by the red line, whereas the red shaded regions show the variability within the population, i.e. the width of the distribution in first figure.

We can see that the nation-wide average resting heart rate at 60,94 beats per minute is nearly constant over the given time frame. In addition, the individual variabilty appears fairly consistant.

A nation-wide resting heart rate map

We can examine the regional variation of this baseline resting heart rate by averaging the values of users in each administrative district in Germany. The results are shown in the map below.

Regarding the community of donors, we can map the resting heart rate for each administrative district in Germany. It shows, values are roughly distributed between 58 and 64 beats per minute.

The average resting heart rate map: This map depicts the color-coded average resting heart rate for each administrative district in Germany. The heart rate varies roughly between 58 and 64 beats per minute on average. These variations appear to be minor, but they are of high importance to this study.

We can see from this map that resting heart rate differs regionally. These differences are snall, but systematic and not by coincidence. In urban areas, the resting heart rate appears consistently lower than in rural settings. Also, we typically see slightly higher values in eastern Germany.

The reasons behind this phenomenon may be multifaceted, yet, are not the focus of this study. The average resting heart rate as a baseline, however, constitutes our most important measure in computing a nation-wide Fever Map.

Note that we cannot yet identify potential COVID-19 Hot Spot regions nor provide information about possible cases of infection or fever from this resting heart rate map

What next?

With the map of the average resting heart rate as a reference, we can now analyze local and temporal deviations. This map is one of the most important intermediate steps on our way towards the Fever Map, which we are currently working on. Further results and intermediate steps are described in our subsequent posts.

In our next post, we will determine the average daily step count of our donors. Most fitness trackers measure daily step count as an indication of daily activity. So, in addition to heart rate, the step count provides us with another important signal.