Many people use a smartwatch to monitor their cardiovascular health, often by counting their daily steps, or recording their average daily heart rate, but researchers have now suggested an enhanced metric, combining the two using basic maths.
Just divide your average daily heart rate by your daily average number of steps, they have said.
The resulting ratio – the daily heart rate per step, or DHRPS – provides insight into how efficiently the heart is working, according to the study by a team at the Feinberg School of Medicine at Northwestern University and published in the Journal of the American Heart Association.
The research found that people whose hearts work less efficiently – by this metric – were more prone to various diseases, including type 2 diabetes, hypertension, heart failure, stroke, coronary atherosclerosis and myocardial infarction, reports The New York Times.
“It’s a measure of inefficiency,” said Zhanlin Chen, a third-year medical student at the Feinberg School of Medicine at Northwestern University and lead author of the study; his co-authors included several Feinberg faculty physicians.
“It looks at how badly your heart is doing,” he added. “You’re just going to have to do a tiny bit of maths.”
Some experts said they saw wisdom in DHRPS as a metric. Dr Peter Aziz, a paediatric cardiologist at the Cleveland Clinic, said it appeared to be an advance on the information provided by daily steps or average heart rate alone.
“What is probably more important for cardio fitness is what your heart does for the amount of work it has to do,” he said. “This is a reasonable way to measure that.”
The metric does not look at heart rate during exercise. But, Aziz said, it still provided an overall sense of efficiency that, importantly, was shown by researchers to have an association with disease.
The size of the study added validity to the findings, Aziz said. The scientists mapped Fitbit data from nearly 7 000 smartwatch users against electronic medical records.
Chen said that a simple way to grasp the value of the new metric was to compare two hypothetical individuals. Both take 10 000 steps a day, but one has an average daily resting heart rate of 80 – in the middle of the healthy range – while the other’s daily resting heart rate is 120.
The first person would have a DHRPS of 0.008, the second 0.012. The higher the ratio, the stronger the signalling of cardiac risk.
In the study, the 6 947 participants were divided into three groups based on their ratios; those with the highest showed a stronger association with disease than other participants did. The DHRPS metric was also better at revealing disease risk than were step counts or heart rates alone, the study found.
“We designed this metric to be low-cost and to use data we’re already collecting,” Chen said. “People who want to be in charge of their own health can do a little bit of maths to figure this out.”
Study details
Daily Heart Rate Per Step (DHRPS): A Wearables Metric Associated with Cardiovascular Disease in a Cross‐Sectional Study of the All of Us Research Programme
Zhanlin Chen, Charles Wang, Carolyn Hu et al.
Published in JAHA on 29 March
Abstract
Background
Simple biometrics such as peak heart rate and exercise duration remain core predictors of cardiovascular disease (CVD). Commercial wearable devices track physical and cardiac electrical activity. Detailed, longitudinal data collection from wearables presents a valuable opportunity to identify new factors associated with CVD.
Methods
This cross‐sectional study analysed 6 947 participants in the Fitbit Bring‐Your‐Own‐Device Project, a subset of the All of Us Research Programme. The primary exposure Daily Heart Rate Per Step (DHRPS) was defined as the average daily heart rate divided by steps per day. Our analysis correlated DHRPS with established CVD factors (type 2 diabetes, hypertension, stroke, heart failure, coronary atherosclerosis, myocardial infarction) as primary outcomes. We also performed a DHRPS‐based phenome‐wide association study (PheWAS) on the spectrum of human disease traits for all 1,789 disease codes across 17 disease categories. Secondary outcomes included maximum metabolic equivalents (METs) achieved on cardiovascular treadmill exercise stress testing.
Results
We examined 5.8 million person‐days and 51 billion total steps of individual‐level Fitbit data paired with electronic health record data. Elevated DHRPS was associated with type 2 diabetes (OR 2.03 [95% CI 1.70‐2.42]), hypertension (OR 1.63 [95% CI 1.32‐2.02]), heart failure (OR 1.77 [95% CI 1.00‐3.14]), and coronary atherosclerosis (OR 1.44 [95% CI 1.14‐1.82]), even after adjusting for daily heart rate and step count. DHRPS also had stronger correlations with max METs achieved on exercise stress testing compared to steps per day (∆ρ=0.04, p<0.001) and heart rate (∆ρ=0.31, p<0.001). Lastly, DHRPS‐based PheWAS demonstrated stronger associations with CVD factors (p<1×10‐55) compared to daily heart rate or step count.
Conclusions
In the All of Us Research Program Fitbit Bring‐Your‐Own‐Device Project, DHRPS was an easy‐to‐calculate wearables metric and was more strongly associated with cardiovascular fitness and CVD outcomes than daily heart rate and step count.
The New York Times article – Using a ‘Tiny Bit of Math’ May Improve Your Heart (Open access)
See more from MedicalBrief archives:
7 000 steps a day can reduce early CVD death risk, global study finds
Under 5 000 daily steps still beneficial, say experts