I recently posted an article on how your smartwatch detects sleep. Here is the next series in line—“Is your smartwatch really smart?” With the advent of cardiac arrest cases in the recent past, most of us find ourselves cautious about our heart health. Heart rate is one among the several parameters that our smartwatch detects. Let’s dive deep and understand how our smartwatch detects this crucial aspect of our health.
Understanding heart rate
Your heart beats a certain number of times per minute- yes, 72 times. This is an average number of course. It can beat slower or faster depending on your age, stress, or physical activity. We measure the heart rate in ‘beats per minute’ (bpm).
Youngsters can have a heart rate ranging from 70-100
People aged over 18 may have heart rates as low as 60-100
Athletes have the lowest heart rates among others as their heart is fine-tuned due to the fitness regime. It thus doesn’t need to exert more force and pump harder.
Using light to detect heart rate
A technology that your watch uses is photoplethysmography (PPG). This complex technique involves shining a light on the skin of your wrist and measuring the change in blood volume because the volume of blood changes with each heartbeat! When blood flows through arteries under the skin, it absorbs some of the light, causing variations in the light reflected to the sensor (on your watch). The software present in the watch then translates it into a heart rate by determining the time between each pulse wave. This technology is essentially reading your pulse through your wrist.
Why is the light source always green?
Your smartwatch emits LED green light onto the skin. Have you ever wondered- why not any other color? The color green is well absorbed by your blood and the optical sensors can accurately detect any change in light intensity. Expanded blood vessels absorb more green light, while contacted blood vessels absorb less green light.
Factors that could give false readings
Sweat, skin tone, and the position of your watch on the wrist could result in false readings. So, always keep in mind these factors before you take these readings to heart! A yet another factor to consider before relying on a smartwatch for heart health is the fact that these measurements are made in the extremities like the wrists. However, blood flow near the heart is faster compared to the tips. It is always accurate to measure the heart beats if the device is placed near the chest.
Can the PPG replace an ECG?
ECG, as you all know stands for electrocardiogram. They measure the electrical impulses in the heart, which is responsible for the expansion and contraction of the heart. In contrast to the PPG, ECG also measures an important factor, known as heart rate variability (HRV). This is the interval between two heartbeats. Our smartwatches use the optical heart rate monitoring (OHRM), I.e. they use light to detect heart rate. This is why your smartwatch cannot accurately determine your heart rate.
While medical diagnosis in the form of ECG is the most accurate way to determine your heart rate, your smartwatch can help you get a guestimate of your heart rate.
Dear readers, what is your take on this? Let me know in the comments.
Fascinating, thanks for sharing!