A person’s heart rate varies throughout the day. At night, a person’s heart rate lowers in order to conserve energy. During a person’s waking period, their heart rate speeds up in anticipation of activity.

The circadian rhythm is an internal clock located in the brain’s hypothalamus that synchronizes all of the physiological functions in the body.

Researchers have developed a statistical method that accounts for all of the noise that might affect a person’s heart rate and extracts a person’s circadian rhythm based on heart rate data provided by their smart watch.

“I think a big question has been, can we measure circadian rhythms with wearables, and how can we do that?” said Forger, also a research professor of computational medicine and bioinformatics at Michigan Medicine.

Researchers developed an algorithm that works by discarding data collected during sleep and focusing on data collected during a person’s waking period.

They also considered whether a person’s heart rate is affected by the person’s activity or cortisol because of exercise, posture, or meals. The result is the underlying daily timekeeping signal controlling heart rate.

To test whether this statistical method worked, the group used a dataset from an ongoing study of medical interns, called the Intern Health Study. The study provides more than 130,000 days of data from 900 interns who continuously wore wrist-based sleep-tracking devices collecting motion and heart rate data.

“Smart watches collect heart rate data using optical sensors, which aren’t very accurate, and there are so many things affecting heart rate throughout the day that measurements tend to be all over the place, so it’s a big result to be able to identify a circadian rhythm in that kind of data at all,” said Bowman, now a professor of mathematics and statistics at Hamilton College.

Smart watches can track circadian rhythm only if measurements are taken frequently and provide information about activity to help account for cardiac demand.

This study also shows that taking a wearable signal and directly measuring circadian rhythms in the real world considers many factors that affect circadian rhythms, which is not possible to measure in the lab.

The researchers also developed the Social Rhythms app, available for iPhone and Android devices, where you can upload your wearable data and receive a report on how your internal circadian clock has changed recently.

Using this information, we will be able to track how the body adjusts to new schedules, how physical activity affects each individual’s heart rate differently, and even quantify the effect of being active at different times of day on the body’s internal clock.

Source: Medindia