Wrist-worn Fitness Monitor Helps in Tracking Changes in PAH Severity

Small study compares Fitbit step and heart rate data with findings of in-clinic tests

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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An illustration of a woman walking.

Step count and heart rate data from wearable sensors can be of use as real-world approximations of common clinical tests of fitness, a study drawing on data from people with pulmonary arterial hypertension (PAH) shows.

“Activity tracker-measured health parameters could serve as proxies for clinically measured health parameters of patients with chronic disease,” Peter Searson, PhD, a professor at Johns Hopkins University and the study’s senior author, said in a press release.

The study, “Evaluation of physical health status beyond daily step count using a wearable activity sensor,” was published in the journal npj Digital Medicine.

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Fitness monitor as proxy for tests of fitness, cardiovascular health

Wearable activity trackers that measure step count and heart rate are becoming commonplace, and an emerging area of research is examining how data collected by these trackers might be used to improve healthcare.

Scientists analyzed data collected from 22 people with PAH, mostly female with average age of 50. All participants underwent two comprehensive clinical assessments, several months apart, where they completed a battery of standardized tests of fitness and cardiovascular health.

Between the two evaluations, patients were given wrist-worn Fitbit fitness trackers. The researchers looked into what could be learned by comparing the 3.5 million minutes of Fitbit data with findings from the clinical assessments.

“Minute-to-minute heart rate and step rate measurements contain a rich array of data associated with physical and cardiovascular function and have the potential to provide much more detailed insight into an individual’s health status based on activities of daily living,” the researchers wrote.

In one analysis, sensor data were used to generate an analog of the six-minute walk distance test (6MWD), a test of physical fitness that measures how far a person can walk in six minutes. Changes in the 6MWD test are a common endpoint, or goal, in pulmonary hypertension clinical trials.

“Timed walk tests provide information on distance and speed, but are labor intensive and hence are impractical to implement at high frequency during hospitalization or outside the clinic,” the researchers wrote.

Insight into a person’s health status based on activities of daily living.

The so-called “free-living” version of the 6MWD was calculated by searching weekly chunks of data for the six-minute period of time with the highest total step count. The step count was then used to calculate distance according to the individual’s height and sex.

Some patients showed a very close association between their free-living 6MWD and their 6MWD tested in the clinic, results showed. Other patients, however, were “underperformers,” meaning their free-living 6MWD was markedly lower than their clinic test.

“These results suggest that the daily activity for the ‘underperformers’ was below their physical capacity,” the researchers wrote.

Subperformance findings “could potentially contribute to the identification of patients who would benefit from more frequent clinic visits or specific medications,” Searson added.

In other analyses, the scientists demonstrated that various other clinically relevant measures of fitness could be approximated using healthcare data. For example, the team used data on average step and heart rate to calculate approximations of physical working capacity — the maximal amount of physical work a person is able to do, usually measured in clinics by assessing how much exercise is needed for a patient’s heart rate to reach a high point.

“These parameters provide weekly signature of an individual’s status that could be used for identifying subgroups within patient populations or assessing changes over time,” the researchers wrote.

Across these measures, the scientists showed statistically significant associations between the data derived from the wearable sensors and those from the in-clinic tests.

“Finding so many statistically significant differences in a relatively small cohort suggests to us that activity-tracker data may make it possible to identify surrogate markers of disease severity that can be monitored remotely,” Searson said.

The team noted that this was a small, single-center study, and further research is needed to validate its results.

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