How Chronic Illness Patients Are 'Hacking' Their Wearables
In the months after giving birth to my son in March 2019, my Fitbit started recording some unusual heart rate readings. Pregnancy causes the resting heart rate to rise about 20 beats per minute, then the rate falls back to its usual levels in the weeks following childbirth. Instead, my resting heart rate continued to steadily rise after birth, a trend that was accompanied by other puzzling symptoms, including exhaustion that wouldn't go away no matter how much I slept; constant, low-grade dizziness; and an inability to return to my former fitness levels, no matter how hard I worked out.
Although finding an answer took years and dozens of doctor's visits and tests, this change in resting heart rate was one of the first clues that I had developed a form of dysautonomia called postural orthostatic tachycardia syndrome.
Wearable tech, such as a Fitbit, Apple Watch, Oura Ring, Whoop, or any number of other commercially available devices, offers a convenient way to collect personal data about our health trends, whether it's information about resting heart rate, heart rate variability, sleep duration, or total activity levels.
What is less clear is what all of this data means, especially when some of the readings are unusual or a person is dealing with symptoms for which they don't have a diagnosis. "What we have right now is a health and wellness industry that provides data-driven insights and data-driven advice, so long as their physiology is typical," says David Putrino, a physical therapy researcher at Mount Sinai in New York City. "What there is a critical need for is applying those same principles to groups of folks with complex chronic illness who have atypical physiology."
For the time being, many patients with chronic illnesses are resorting to cobbling together a system that works for them, based on their own knowledge about their condition and the data they can access using a variety of health trackers, all while navigating life with chronic illness, where symptoms fluctuate day-to-day.
For many patients, this creativity is borne out of desperation, as a number of these illnesses, whether it's long Covid, dysautonomia, or myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), have very few treatments available and even fewer specialists who are trained in recognizing and treating them. "We're being forced to do it ourselves, because the system is not set up to address these more complex and invisible conditions," says Spencer Gudewill, a patient with post-concussion syndrome and the cofounder of the Strong Haulers, which aims to help people with chronic illness manage their condition using wearable tech. "A lot of people slip through the cracks."
Resting heart rate has long been used as a metric of overall health, with average values being between 60 and 100. People who are in good health and have a higher level of fitness tend to have lower heart rates, as their hearts are generally stronger and more efficient, with trained athletes often reporting resting heart rates that are lower than 60 beats per minute. A higher resting heart rate, or an increases over time, is often an indicator of poorer health, including an elevated risk for heart attack.
Short-term changes in resting heart rate are often used by athletes to gauge whether they are overtraining, while changes can also be a sign of an infection, such as the flu or Covid. In a study published in the Journal of the American Medical Association using Fitbit data, researchers found that, on average, a Covid infection caused an increase in resting heart rate that took about 79 days to return to normal.
Although changes in resting heart rate can be a useful indicator of a person's health, the disadvantage is that resting heart rate tends to stay relatively stable throughout the course of a person's life, which means that any changes tend to be incremental and can take a while to detect as meaningful.
In the fall of 2021, when I knew something wasn't right but I just couldn't get my doctors to take me seriously, I bought an Oura Ring in a fit of desperation, to wear in conjunction with my Fitbit. One of the reasons for my purchase was that it offered nighttime heart rate variability tracking. In theory, heart rate variability (or HRV) could offer some additional insights, which could be complementary to the changes I was already seeing in my resting heart rate, but only if I knew what to make of it.
Heart rate variability, which is the variation in timing between heartbeats, offers a complementary look at overall health, in part because it is an indirect look at how a person's autonomic nervous system is functioning. HRV values typically range from 20 to 200 milliseconds, with a higher HRV being a sign that a person's autonomic nervous system is highly responsive, whether it's telling your heart to beat faster or slower, your blood vessels to constrict or dilate, or your digestion to speed up or slow down. "The extent to which your autonomic nervous system can make very small but highly specific changes, that's an indicator that you have a highly optimized, healthy system," Putrino says. It's this insight into the autonomic nervous system that is often helpful for patients with chronic illness, as lower HRV is a sign that the body is under a lot of strain.
The major issue with tracking HRV is that the numbers are hard to make sense of, as the values are highly variable, including a wide range in average values from person to person, and even a wide variation from hour-to-hour, depending on a person's health and environment. It's these wide ranges in values that make HRV so confusing to interpret and also doesn't lend well to once-a-year health checkups. However, when these averages are looked at over time, they can offer some useful insights.
For Tess Falor, a patient with ME/CFS, noticing an eight-month decline in average nighttime HRV was what caused her to realize she'd been taking on too many work projects, which was resulting in a worsening of her condition. "You couldn't really tell, because it was happening slowly," says Falor, who cofounded the patient-led organization Remission Biome, which studies the impact of the microbiome on ME/CFS symptoms.
Falor, who has regularly been wearing a FitBit since 2009, also uses heart rate tracking to avoid overexertion, which can lead to debilitating crashes. She has found that keeping her heart rate under a certain threshold helps her avoid these crashes more accurately than if she were just monitoring her symptoms. "Listening to my body is not enough," Falor says.
For Ibrahim Rashid, a patient with long Covid, combining symptom tracking with HRV led him to correlate his levels of increasing leg pain, which at times was so bad he needed a wheelchair, with trends in decreasing HRV.
He has also found that correlating his symptoms with his health data helped him make judgment calls on what helps the most with managing his symptoms, such as limiting stress, and what only has a minimal effect, such as cutting out all sugar. "You spend so much time trying to figure out what works and what doesn't," says Rashid, also a cofounder of Strong Haulers.
For Harry Leeming, the confusion of trying to manage his long Covid symptoms, combined with the difficulties of adapting wearable tech to his needs, were his primary motivation for developing the Visible app. He's now testing out a wearable that gives him feedback on how much time he spends in an upright position, which he's finding correlates to the severity of his symptoms.
In my own case, the fact that my HRV was unusually low and didn't respond in the usual ways to lifestyle changes ended up being another clue that the underlying issue was a disorder of the autonomic nervous system. After months of tracking, I was also able to look at the trends in average HRV and correlate periods of declining HRV numbers with periods when my symptoms were especially bad, my own personal early warning system for when a major flare might be coming. After receiving a formal diagnosis and starting treatment, which included medication and additional lifestyle modifications, my symptoms have started improving, along with my average nighttime HRV. "Arguably, the signals are stronger, and the data is far more actionable" for people living with chronic illness, Leeming says.