Summary
- Wearable devices can make non-intrusive measurements of digital biomarkers.
- Regular digital measurements can help recognize disease development.
- Wearables are a good screening tool for disease, but can be followed up with more sophisticated and specific tests once disease potential has been identified.
“I have to get my 10,000 steps.” How many times have you said that or heard a friend or colleague say that? Before 2009, probably never. But in the fall of 2009, the fitness tracker called Fitbit was first introduced. The success of the Fitbit has led to the proliferation of other fitness trackers from Apple, Garmin, Samsung, and others. These were not the first fitness trackers (pedometers have been around for decades), but these allowed people to incorporate the device in a form they might be wearing anyway. So now everyone has a way to know if they are near or have passed their 10,000 steps. Why 10,000 steps? Ten thousand steps approximately meets the Centers for Disease Control and Prevention’s recommendation of thirty minutes of daily exercise per day, and makes an easily remembered goal for people. With the addition of digital sensors, these fitness trackers can measure a lot more than just your steps. They can measure heart rate, sleep quality, stairs climbed, and time spent performing active exercise, among other variables that can be routed to an app on your phone, so you can analyze how you are doing.
What are wearable devices, and how do they work?
Wearable devices capture activity and movement through the incorporation of an accelerometer. This electromechanical device measures forces associated with acceleration, such as in a vibration, shock, or when you move your arm or body for exercise. Acceleration is classically calculated by dividing the change in velocity over a specific time period (acceleration = ∆ velocity / ∆ time), so the device measures the changes in movement per period of time to determine activity level. The green lights on the back side of a Fitbit are light-emitting diodes (LEDs) that flash many times per second. Each time these flash through your skin, photodiodes in the Fitbit can detect the blood volume changes in the capillaries just below the surface, allowing for the measurement of heart rate. The Fitbit can also estimate how many flights of stairs you walk up, whether you are walking up actual stairs or walking up a steep hill on a mountain climb. Visible as a small hole in the side of the Fitbit, an air pressure sensor measures the elevation. The distance you travel in a day is tracked either by the Global Positioning System (GPS) or by calculation based on the number of steps you make and the length of stride (as calculated via the height input into the app). All of these functions and features make wearable devices potentially valuable tools in determining an individual’s health without needing to travel to a doctor’s office or take blood samples.
How can wearable devices be used in medicine?
The vast amount of continuous data generated by these wearable devices is being used to determine if people can be screened for a previously unknown disease. A study presented at the 2021 American Heart Association Scientific Sessions showed that by accumulating data of activity levels over long durations, software algorithms could identify people experiencing atrial fibrillation (AF), putting them at higher risk of later stroke1. This screening tool of everyday data was then used to have subjects come into a doctor’s office to confirm the AF with an electrocardiogram (ECG) patch monitor.
An ongoing study at Duke University is recruiting subjects to investigate if using the data from a digital device can help study SARS-CoV-2 infections2. The device would measure blood oxygen levels and heart rate, and researchers would determine if these measurements can predict infection or severity of SARS-CoV-2. These predictions could then be confirmed with the results of an RT-qPCR assay for SARS-CoV-2 such as the
AMPIPROBE SARS-CoV-2 Test System, which is used in the extraction, purification, and amplification of SARS-CoV-2 RNA.
Another multi-institutional group gave subjects accelerometers to measure activity levels after having heart failure but preserved ejection fraction3. They gave the subjects a placebo or isosorbide mononitrate, a nitrate commonly given to patients with heart failure to increase their ability to exercise. They found that isosorbide mononitrate was unexpectedly associated with decreased activity levels, with no differences in levels of N-terminal pro-brain natriuretic peptide (NT-proBNP), a peptide associated with previous heart failure (HF). Similar future explorative studies can monitor this important HF biomarker with the
BNP Fragment ELISA kit. The use of mobile accelerometers allows for studies of activity to be incorporated into people’s everyday lives and outside of an office with sophisticated metabolic chambers.
The US Food and Drug Administration (FDA) describes the use of “computing platforms, connectivity, software, and sensors for health care” as Digital Health4. Digital Health includes the use of radio frequency (RF) wireless devices that use Wi-Fi, Bluetooth, or other wireless communication to interact with a cell phone or other computer to monitor data. Some exciting applications of non-invasive Digital Health are in the fields of Diabetes and Heart Disease monitoring. In the past (and still today), diabetic patients monitor their blood glucose multiple times over a day after pricking the skin with a needle. Measuring blood glucose without causing physical pain would be an excellent quality of life improvement for Type 1 and Type 2 diabetics. Some companies have developed Continuous Glucose Monitoring (CGM) systems that utilize a sensor under the skin (Table 1), so there are fewer skin breaks. After initial placement, measurements can be monitored on a smartwatch or phone app. By being able to sample multiple times in shorter periods than with finger sticks, the user can also have more information about how fast their blood glucose levels are rising or falling and can take appropriate compensatory actions if necessary.
Monitor |
FDA Approval |
Manufacturer |
Time to Sensor Replacement |
FreeStyle Libre |
2017 |
Abbot Diabetes Care |
14 days |
Eversense CGM |
2019 |
Senseonics |
90 days |
Dexcom6 CGM |
2018 |
Dexcom |
10 days |
Guardian Connect |
2018 |
Medtronic |
7 days |
|
Table 1. Selection of Available Glucose Monitors
|
High amounts of cholesterol, the fat-like substance that builds up on blood vessels and clogs arteries, is one of the significant risk factors for heart disease. Cholesterol is commonly detected after a fast of 8 to 12 hours , followed by a blood draw in a doctor’s office. Companies and researchers have also been trying to develop non-invasive devices to measure cholesterol without the need for a blood draw. The first such test approved by the FDA, from International Medical Innovations in 2002, was called Cholesterol 1, 2, 3, and measured the amount of cholesterol in the skin. Unfortunately, while Cholesterol 1, 2, 3 measures the build-up of cholesterol in tissues, results from this device are not representative of blood cholesterol level. Others also measure skin cholesterol but claim the results correlate to the blood. One such system uses chemicals that fluoresce in the presence of cholesterol in skin oil from the palm of the hand and can be scanned by light scatter to measure the spectral signature before and after the addition of the chemical. 5
How can Enzo help guide your research?
Wearable devices are now a part of everyday life, and we will only be seeing more uses developed to improve human health. Do you have more questions on wearable devices and how to find the best assays to confirm digital data? Reach out to our
Technical Support Team. We will be happy to assist!
