It's been nearly four years since Apple ResearchKit was announced - a platform that allowed Apple to harness the iPhone and Apple Watch for clinical purposes and further its health and wellness ambitions.
However, while the iPhone's app ecosystem was already mature and ready to welcome partners for research at that time, the Apple Watch, which only launched in 2015, has taken more time to be adopted successfully in trials. We're now seeing the potential of its innate tracking capabilities, though, and some of the early studies hint at how powerful the device could be in years to come.
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Here's six key studies and health conditions the Apple Watch has been tasked with tackling so far - but check back, as it's likely there'll be more that come to light over the course of 2019.
Apple Heart Study
We'll kick things off with perhaps the most well known study involving the Apple Watch (and one of the few that we've seen the published results of), the Apple Heart Study.
In collaboration with Stanford University Medicine, 419,000 participants from 50 US states across an eight-month period enrolled to the study, with the hope that Apple's smartwatch could accurately detect an irregular heart rhythm. As an irregular beat is indicative of atrial fibrillation, this also tied in nicely with the ECG monitoring feature that landed through the Apple Watch Series 4 - something we'll come onto below.
However, for this study, participants were monitored using the Apple Watch Series 1, 2 and 3 - none of which have an ECG - with the optical heart rate sensor being used to detect irregularities.
The results? Well, 0.5% of participants received warnings of irregular rhythms; 84% of those who did were found to be accurately in AFib episodes at the time of the detection; and one third of participants who got an irregular pulse notification and went on to use the ECG patch did actually have AFib.
Does that mean the Apple Watch can be an effective screening tool for irregular heartbeats? Well, maybe - in truth, it's too early to say. And there was definitely limitations, as we broke down in our Apple Heart Study analysis.
We should also note that, in May 2017, there was a study conducted by the University of California and the Cardiogram app, which found the Watch could be used to detect abnormal heart rhythms with up to 97% accuracy.
Atrial fibrillation (again)
The Apple Heart Study is the study that marks the Apple Watch's big dip into health, but the company has also outlined details regarding the accuracy of its ECG monitor on the Series 4 - this time through a study with less participants than the Heart Study.
In a clinical trial involving 600 people, the ECG app on Apple Watch was compared to a standard 12-lead ECG reading taken at the same time. The findings demonstrated the smartwatch's ability to accurate accurately turn an ECG recording into AFib (99.6%) and sinus rhythm (98.3%) classifications.
Is this better than medical-grade technology, then? Well, not exactly. With the ECG app representing a waveform similar to one of the 12 produced by a 12-lead machine, it can't, for example, pick up on conditions like heart attacks. However, even producing one waveform with accuracy allows the Apple Watch to screen for heart rhythms and AFib.
Binge eating and bulimia
In 2018, Apple donated 1,000 Apple Watch devices to a study related to overeating and bulimia nervosa, conducted by the University of North Carolina.
The study looked to identify biological changes brought on by excessive eating, or even by over-exercising and purging. In the month-long study, the researchers analyzed whether the Watch's heart rate sensor could detect the changes associated with the symptoms.
It also partnered with app Recovery Road, available on both iOS and watchOS, in order to gain more insight into participant's eating patterns and feeling toward eating. This joined the health and heart data already recorded by the Watch, as well as genetic and bacteria tests taken to try expose an underlying cause of the disease.
We're yet to see the results of this study be published.
Johns Hopkins University has already harnessed the Apple Watch to help participants with epilepsy register their seizures.
Working from an app called EpiWatch, built using ResearchKit, participants were able to tap the Apple Watch complication when they felt a seizure starting, with the device then recording heart rate and movements for 10 minutes. It also asked the user to perform tasks in order to gauge responsiveness, with the option to send an SOS alert, too.
Essential reading: What is Apple CareKit?
The findings of the ten-month study showed that stress was the most common trigger of seizures, with a link in 37% of cases. A lack of sleep was also found to be a trigger in 18% of cases, with menstruation (12%) and overexertion (11%) also linked. These triggers, interestingly, did not vary by the type of seizure someone had, either.
The study found that stress was reported more often with people in full-time jobs (35%) than those in part-time (21%), while unemployed (27%) and disabled people (29%) also logged less stress.
Zimmer Biomet, a medical device company, have teamed up with the Apple and its smartwatch in order to create an app called MyMobility.
The aim is to combine this with the data collected by the Watch in order to figure out why certain knee and hip replacement patients recover faster than others. The results of the study are yet to be published, but the company was looking for 10,000 subjects to analyze.
The hope was that if the patient was able to share information such as steps and heart rate data with their doctor, it would provide a clearer picture of they were performing post-surgery. So, for example, if a patient was concerned about the level of pain, the doctor could assess the data and see if the cause was as a result of overexertion.
The University of North Carolina used the Apple Watch to help develop a study surrounding postpartum depression.
Looking to collect data through its PPD Act app, the initiative is aiming to find out if there's a genetic disposition attached to the condition, with the Apple Watch also a way for users to personalize their participation further. If they choose to consent, women are sent a spit kit to test their DNA, with this then combined with feedback given through the app regarding the Edinburgh Postnatal Depression Scale.
The initial goal was to get 100,000 women from around the world to take part in the study, though the findings have yet to be published from the study.