A young gym-goer frantically telephoned a cardiologist after his smartwatch showed a heart rate of 38 beats per minute since the normal is usually between 60 and 100. “When he removed and re-wore the watch, it showed 100 bpm. It was clearly an error, but it caused him immense anxiety.”
Wearable fitness trackers and smartwatches have become quite ambiquitous as we increasingly rely on data to tell us how much we walked, ran, swam, and slept. There are even glucose monitors which tell us, how a particular meal affected us. But what if that turns into an obsession? What if the readings aren’t as accurate as you think them to be?
Medical experts are raising red flags about young patients obsessively monitoring their health metrics and rushing to them in a panic, merely because their smartwatch displayed an elevated or reduced heart rate. “They are constantly checking the heart rates displayed. These devices actually show the pulse rate, and people don’t understand the difference between the two.”
Smartwatches use photoplehysmography (PPG) to measure the heart rate by monitoring changes in blood flow with each heartbeat. “Heart rate is truly gauged via an electrocardiogram (ECG) or by putting a monitor on the heart. PPG does a fair job but it’s not nearly as accurate as an ECG.”
Small movements can disturb the pulse rate, affecting smartwatch readings, which can lead to inaccuracies and a vicious cycle of anxiety. “When there is fear, their heart rate rate increases as per the smartwatch, which makes them even more paranoid. If tracking heart rate or BP becomes an obsessive-compulsive disorder, it’s a psychiatric issue,”
Patients call at odd hours, just because their smartwatch showed high or low heart rates. Too much worry can cause arrhythmias due to hormones released by the body.
“The smartwatch ECG is still limited in terms of accuracy and possible diagnoses ( it only aims to detect AF, there are many other anomalies). The ECG quality can be close to medical grade, but lack of knowledge regarding ECG interpretation and t he limitations of today’s automatic algorithms means perfect results cannot be expected from a smartwatch.”
So it’s risky to place too much faith on the smartwatch. “When there’s a cardiac anomaly and the smartwatch ECG shows as ‘normal’, the patient may not seek medical attention which could be dangerous. Potentially fatal myocardial infarction, with acute blockage of a coronary artery, show up on the ECG. But the smartwatch does not look for those signs so the diagnosis will be missed.”
Newly popular sleep trackers claim to calculate awake, REM (rapid eye movement) and deep sleep stages each night, giving a sleep score on a scaled of 0-100, with higher scores indicating better sleep. But experts caution against taking these scores at face value. Smartwatches use sensors like an accelerometer, gyroscope and heart rate monitor, which don’t detect sleep stages. “Actual sleep is measured through a sleep-electroncephalogram (EEG).
Smartwatches detect sleep based on wearer movement. If the wearer isn’t moving, it’s counted as sleep period. Many patients get unduly worried if they don’t get ideal sleep scores.”
Even calorie-burn estimations can widely vary. “These devices accurately track heart rate across activities, skin tones and body types, but do not estimate calories nearly as accurately.”
It adds to the unconscious bias against people who may not fit the stereotypical profile of ‘healthy’ as imagined by developers. While that may be a bit drastic, doctors say it’s best not to overly rely on data and listen to your body.
STEP COUNT TO SLEEP, HOW ACCURATE IS YOUR WEARABLE?
- Can measure heart rate with an error rate of plus or minus 3%. Can also accurately measure heart rate variability and show good sensitivity and specificity for detecting arrhythmia, a problem with the rate of a person’s heart beat.
- Generally underestimates step counts by about 9%.
- When it comes to calorie burn, error margins range between 21.3% and 14.7%, depending on the device and the activity.
- Overestimates total sleep time and sleep efficiency by more than 10%.
