At a time when usage of smartwatches and rings has become more common, a West Virginia University human performance researcher points out that the heart rate variability—the time between heartbeats—the devices report is different from what would be recorded in a clinical setting. "Heart rate variability has been used for nearly 100 years as a non-invasive measure of the autonomic nervous system, having been linked to overall mortality, cardiovascular health and stress," said Matt Tenan, program director for Human Performance Research and Data Science at the WVU Rockefeller Neuroscience Institute. "Consumer wearables are reporting heart rate variability data and metrics that previously you would only get in the hospital and a lab setting, but they're recording them differently.
" Wearables operate with photoplethysmography, or PPG, a technology that shines a light into the skin and produces a reflection of the blood moving just below the finger or wrist to record heart rate. In a hospital, an electrocardiography—ECG or EKG—machine measures the heart's electrical activity through electrodes placed on the body. "You're looking at two things, one is blood flow and the other is the electrical signal of the heart," Tenan said.
Clinicians and medical scientists are interested in heart rate variability because it's a biomarker for a patient's general systemic health. Tenan said even if people don't pay particular attention to the measure on their wearable, it still plays a par.