10-06-2021 | | By Robin Mitchell
Recently, Apple launched a new app for their smartwatch devices in Australia that monitors heart erythema and warns users of their condition. How do most smart devices monitor heart rate, why are these devices not true ECGs, and how can they still be helpful?
Measuring heart rate is surprisingly easy to do, and most smartphones are capable of doing this through free apps. In most cases, the device requires that the user places their finger over their camera, and then the flash turns on. During this time, they are asked to remain steady, and eventually, a heart rate is measured as well as the changes in blood flow.
Such devices work by taking advantage of the minute change in optical transparency in body tissue during consecutive heartbeats. As the heart beats, it increases blood pressure, and this forces the blood around the body. At the same time, blood that is rapidly expanding into arteries and capillaries makes the surrounding tissue appear darker as it can absorb more light. As the heart rests and the blood pressure falls, the tissue becomes more transparent (albeit extremely lightly).
When a finger is placed onto the camera and flash of a smartphone, the light from the flash penetrates the tissue in the finger. The camera can detect the resulting colour of the finger, and as the blood pressure rises the colour of the finger deepens (more specifically, the transmitted light falls). The initial use of such apps requires time to calibrate the camera reading to ignore ambient light which is why users need to stay still. Eventually, the “DC” effect of the ambient light is removed from the camera output, and the resulting beats of the heart cause noticeable changes in the detected light. Thus, a basic routine can look at the lows and highs from the camera and infer the BPM using a timer.
Before we look into the new app being released by Apple, we first need to address the incorrect usage of “ECG”. While most recognise that ECGs measure heart rate, the truth is that ECGs actually measure the electrical activity of the heart (hence the term Electro-Cardio-Gram). An ECG requires a multitude of special electrodes placed around the body including the leg and across the chest (sometimes for a total of 12 electrodes). These electrodes measure the electrical potential across the heart from various points and can be used to detect the tiniest fibrillation and flutters.
However, devices that use light are not ECGs, and merely measure the changes in blood pressure that cause changes in the colour of skin. As such, light-based systems cannot be used to detect tiny irregularities in the heart and are more ideal for just measuring heart rate.
Recently, Apple has announced the release of their new heart-rate monitoring app for their smartwatches in Australia. The aim of the new app is not just to measure heart rate, but to measure irregularities in heart rate. If more than 5 irregularities are measured in a given time (around 65 minutes), the app warns the user of the readings. It is hoped that such a system can provide people with a safeguard against potential underlying health conditions that may have gone unnoticed.
It is also hoped that the gathering of heart data from users will help Apple to develop more accurate systems with the use of deep learning. From there, updates to the app will allow for it to be more sensitive and thus produce more accurate results.
It is possible to measure some biological data from a distance (some of the iPads can measure heart rate just by looking at the face), but it is more likely that wearable devices will be heavily used in the medical field. Furthermore, wearable devices can be geared to provide primary functions such as messaging and browsing but provide medical data in the background at all times.
What used to require large surveys and experiments with thousands of volunteers can now be done at no cost with the many hundreds of thousands of users of wearable devices. With the permission of the users, medical professionals will be able to have more data than they could ever dream of, and this could spark a new medical revolution.