The A to Z of HRV and to use it in your digital health app

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If you count how many times your heart beats per minute, you might arrive at a similar number from one minute to the next. But did you know that the amount of time between those heartbeats can vary? This is called heart rate variability, or HRV.

Researchers have found that HRV can be a useful biomarker in analyzing a person’s fitness levels, stress levels, adaptability, and risk for some diseases and conditions, as well as in understanding other aspects of health and wellness. In fact, more and more digital health companies are incorporating HRV measuring and tracking tools into their technology products and services, resulting in the general population having more access to this important information.

HRV facts

If your heart beats 60 times per minute, for example, those 60 beats are not perfectly spaced out one second apart. There are subtle fluctuations in the amount of time between heartbeats. It’s the variability in these fluctuations that can provide insight into a person’s health.

What do HRV trends tell us?

Our heart rate is controlled by a part of our nervous system known as the autonomic nervous system (ANS), which also regulates other bodily functions like blood pressure, breathing, and digestion.

Within the ANS, there are the sympathetic (fight or flight) and the parasympathetic (rest and digest) nervous systems. Together, the sympathetic and parasympathetic nervous systems send signals to the heart to beat faster or slower — and heart rate is another thing that affects HRV: when your heart is beating faster, there are typically fewer variations between heartbeats; when there is more time between heartbeats, there is more time for variations.

Having a high rate of variability often means that your body is responding efficiently to both parasympathetic and sympathetic inputs. In other words, your body’s nervous system is capable of adapting to its environment. This allows you to perform at your best in a variety of situations — including under high stress. As Frontiers in Public Health reports, “The oscillations of a healthy heart are complex and constantly changing, which allow the cardiovascular system to rapidly adjust to sudden physical and psychological challenges to homeostasis.”

So a higher HRV is one indicator of health, and it’s a sign that your body is able to get into a relaxed state more readily. A lower HRV may indicate that your body is operating too often in, or moves too frequently into, “fight or flight” mode.

What is the relationship between HRV and other metrics?

In addition to being a sign of potential health problems, low HRV may indicate certain diseases or conditions, and it’s often accompanied by other signs of poor health. If you consider the ways that HRV is influenced by the autonomic nervous system, you can see how HRV impacts a wide range of bodily systems.

Blood pressure: Hypertension and lower HRV tend to go hand in hand. In one study, HRV was shown to be significantly lower in hypertensive men and women. Also, among men with normal blood pressure, lower HRV was associated with a greater risk of developing hypertension.

Cardiovascular health: In another study, lower HRV was linked with a twofold increased risk for the presence of myocardial ischemia — a serious heart condition — in individuals without known coronary artery disease (CAD). HRV values have also been shown to be low in patients with CAD, “and low HRV has been shown to be an independent predictor of cardiovascular mortality and sudden cardiac death,” according to researchers.

COVID-19 and HRV: According to research published in the journal PLOS One, higher HRV predicts greater survival rates in people with COVID-19, particularly those who are 70 years old or older. Meanwhile, lower HRV presents a greater risk for admission into intensive care within the first week after hospitalization with COVID-19.

It’s important to note that lower HRV will not typically cause a medical emergency immediately. However, over time, it can indicate the possibility of current or future health issues.

Also, a healthy HRV level for one person may be unhealthy for someone else, due to the complex nature of HRV. A higher HRV does not necessarily mean someone is free and clear of health issues, either. Working together with a doctor to address any questions or concerns is always the safest bet.

How is HRV measured?

Measuring HRV requires either a medical device called an electrocardiograph (ECG or EKG) or a non-medical device you can purchase for personal use. An EKG measures the electrical activity of your heart via sensors attached to your chest. Non-medical devices function similarly but may have a sensor that picks up data through a different part of the body, such as a wrist or an ear. These wearable devices have become more widely available and affordable with the increase in HRV research in recent years.

Whether in a medical setting or a non-medical one, HRV monitors collect and analyze data on the milliseconds of time between heartbeats, known as RR intervals. These intervals appear between the “spikes” you see on a heart rate reading when a heartbeat occurs.

What affects HRV, and how can you improve It?

By tracking HRV data, you can see trends over time and take steps to improve your HRV. Research has shown that HRV is affected by a wide variety of factors, including:

Age: Older adults tend to have lower HRV than younger people.

Fitness levels: Research has found that fit people tend to have higher HRV than unfit people.

Stress levels: Stress can suppress our parasympathetic nervous system's ability to regulate our heart rates effectively. Over time, this may lead to low HRV.

The good news is that it’s possible to improve HRV with simple lifestyle changes. Exercising and eating a healthy diet can help to boost heart health (and overall health), which can improve HRV. Taking steps to reduce and manage stress, as well as to address mental health issues such as anxiety and depression can help, too. In addition, controlling your breathing through biofeedback training is another step toward better HRV.

How can digital health companies leverage HRV in their offerings?

The era of wearable tech has presented many opportunities for the development of new devices aimed at measuring, tracking, and analyzing HRV..

Use cases

Nutrition app

As we’ve discussed, the ANS is closely linked with bodily processes, including digestion and inflammation.

So measuring HRV could help uncover a need to make dietary changes. A lower HRV could indicate inflammation or digestive issues, and a nutrition app that lets users track HRV alongside their dietary intake could help them see any patterns linking lower HRV with certain foods. They could then better understand whether any foods are triggering a negative physiological response and eliminate them from their diet before the foods cause symptoms.

Fitness app

In the context of fitness, understanding HRV may help to better inform workout sessions. Measuring HRV before a workout provides insight into stress levels and how ready a person is for any particular workout. A higher HRV could mean the body is recovering from prior training sessions and any other stressors.

In contrast, a lower HRV may indicate that a person is still in recovery mode and might not be up for a challenging workout. While the body recovers, it’s important not to place more demands on it, as this could interfere with proper fuel utilization and hormone production or result in overtraining, injury, or a further lowering of HRV.

With this kind of insight built into a fitness app, you could easily see what kind of workout is best from one day to the next. Personal trainers using such technology would also have a better way of designing customized workouts, informed by HRV, for each client.

Remote patient monitoring platform

From a doctor’s point of view, having greater insights into a patient’s HRV can prove to be a useful noninvasive research tool in cardiology. In clinical practice, HRV measurements can help a physician to estimate the risk of arrhythmias. In addition, any decreases in HRV may be helpful clinical markers for diabetic neuropathy or other developing diseases. Having HRV tools integrated into an app could allow doctors to monitor HRV data based on patient-specific thresholds and be proactive when changes occur.

How can digital health companies collect HRV data?

Digital health companies have an opportunity to make HRV an integral part of their offerings. So how can these companies collect HRV data? Here are two options:

Build integrations with all of these devices separately: This route is costly and time-consuming, potentially overstretching your resources and budget. It is also challenging to maintain each of these integrations over time and would likely take an entire engineering team.

Vital Wearables API: Vital connects digital health companies with the infrastructure they need to incorporate high-quality HRV data into their own offerings from wearables and medical devices. Instead of building integrations with hundreds of devices in-house, Vital’s API lets you collect all of this data from one integration. Vital supports the majority of fitness and wellness devices, so your company can start collecting health or fitness data, build your remote patient monitoring or fitness app, and begin getting insights from data to display for your users in less than a day.

The ability to collect accurate and precise HRV data is an essential component of digital health and wellness monitoring. As more companies develop HRV measurement tools, digital health companies have the opportunity to use this metric as a key part of their offerings. By partnering with a company like Vital or developing their own in-house solutions, digital health companies can make use of HRV data to improve all areas of their customers’ health.

To learn more about how Vital can help you save thousands of dollars in engineering costs (see how we saved Fastic $450k in wearables integration costs) and help you make use of HRV (and other health) data, check out our developer documentation to get started!