U-M, Apple Watch study: An unprecedented look at health status of a diverse patient population

October 26, 2021
Written By:
Kelly Malcom

Illustration of an Apple Watch.Wearable technology such as the Apple Watch is allowing researchers to recruit a more diverse group of participants to health and wellness studies, helping them better understand the underlying health conditions they could only dream about glimpsing at before, according to a new three-year landmark observational University of Michigan study.

Published in The Lancet Digital Health, the study looked at data from nearly 7,000 participants who wore their Apple Watch on almost 90% of the study days for an average of 15.5 hours a day. Overall, 1.1 million blood pressure and more than 200 million heart rate measurements were collected through study devices.

The paper examines the first 90 days of the study, describing blood pressure, heart rate and activity data collected with the Apple Watch or iPhone and blood pressure measurements collected with the Omron wireless blood pressure cuff.

Participants 65 and older had significantly lower resting and walking heart rates, and women had resting heart rates on average 3 beats per minute higher than men. When stratified by self-declared race, Black participants had the highest heart rates and white participants the lowest. Activity levels also varied by race and ethnicity and by the presence of certain clinical conditions.

Together, these differences demonstrate that patient-specific context is an important consideration when clinicians interpret wearable and home blood pressure data, said study co-investigator Jessica Golbus of U-M Health’s Division of Cardiovascular Medicine, noting that 10% of participants had diabetes, a third had hypertension and more than a quarter of participants reported depression.

“As a cardiologist who takes care of patients dealing with heart failure, it’s important that more than 200 patients in our study have heart failure,” she said. “Understanding what their baseline information looks like is going to be really informative and allow us to start with more accurate estimates of patients’ activity levels in daily life.”

Golbus said that one of the biggest successes of the study so far was their ability to recruit from groups that have largely been underrepresented or unrepresented in digital health research. For example, 18% of the nearly 7,000 participants were 65 or older, 17 percent were Black and 17% were Asian.

Researchers also note that unlike other studies, this paper includes 90 days of data provided by the MIPACT study, but also offers a more representative sample of participants’ long- term experiences.

For the study, participants were recruited through phone calls, social media, in clinic recruitment and community events. They were asked to complete baseline surveys, donate a blood sample, wear the Apple Watch 12 hours a day and complete breathing and blood pressure checks twice a day during the first phase of the study.

From a technology standpoint, the study revealed a significant discrepancy in activity levels as measured by the watch and phone, with the latter underestimating step counts.

“I think what this means is that not all mobile device signals are created equal and that, in the future, interpretation of these signals will require knowledge of the device from which these signals were collected,” Golbus said.

Summary data across participants is available in a web-based research tool developed by the study investigators.

“With this tool, researchers and participants can choose certain clinical and demographic criteria—age, body mass index, sex—and see not only how many participants fall into that cohort but their average resting heart rate, blood pressure and other activity data,” said Nicole Eyrich, clinical research project manager for the MIPACT study. “It provides more context in the form of normative data for researchers.”

The study, which aims to enroll a diverse set of participants across a range of ages, races, ethnicities and underlying health conditions, is led by Sachin Kheterpal, associate dean for research information technology and professor of anesthesiology and launched in 2018 as a collaboration with Apple.

Golbus said the ultimate results of the study will be important clinically for physicians.

“Pretty frequently, I get asked by my patients what their wearable device data means, and it’s really challenging to understand its implications for their long-term health,” she said.

She says that the three-year follow-up period will be most informative as they seek to contextualize the data signals from the Apple Watch with information from participants’ electronic medical records and survey data. The data may also provide the unexpected ability to examine the effects of the COVID-19 pandemic.

“We have data on participants both before and after the onset of the pandemic, so we really have the capability to evaluate how physiologic parameters changed over the course of the pandemic both as a result of illness but also due the global impact the pandemic has had on all of our lifestyles,” Golbus said.


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