Heart Rate Variability

Heart rate variability is a new technique in the field of biofeedback that can help provide a more accurate picture of your physical and emotional state. This blog post will explore what heart rate variability is, how it works, and some benefits you may see from using this new way to track well-being. 

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Heart Rate Variability (HRV) is thought to be originally discovered by K. Grinberg back in 1896 but was not researched until the 1960s. Heart rate variability is a measurement of the time between heartbeats. It can be measured in milliseconds, which are 1/1,000th of a second. HRV is measured by your heart’s response to breathing patterns. As you breathe in, your body absorbs oxygen and nutrients that allow the lungs to release carbon dioxide when you exhale. As the body absorbs oxygen, it sends an electrical signal to the heart muscles to contract. This contraction is what pushes blood throughout your body via the circulatory system. During exhalation, there is less pressure on your heart since no new air comes in with each breath (and you exhale carbon dioxide). A low HRV value means that it takes longer for the heart to relax and fill with blood between beats, causing reduced circulation throughout the body. 

HRV AND SLEEP

Sleep is critical to our overall health.  Not only does our body use this time to repair itself, but it is also an opportunity for the brain to go through stages of mental development. The average adult sleeps 7-8 hours per night. However, not all sleep is created equal. There are 4 stages of sleep and two types of sleep: rapid eye movement (REM) sleep and non-REM sleep (which has three different stages). 

Stage 1: is non-REM sleep. It is described as light sleep and you can be lightly stimulated without waking up. Additionally, your brain waves begin to slow down compared to your daytime activity. 

Stage 2: This stage is a deeper non-REM sleep. It is more difficult to be woken up during this phase, your brain waves further slow down and your body temperature begins to drop.

Stages 3: In these final stages of non-REM sleep, there are very slow brain waves called delta waves.  

Stage 4: REM Sleep. Rem sleep is when your eyes move rapidly back and forth behind your closed eyelids, where you are in a deep sleep but dreaming.

RV is very important when it comes to sleep. In fact, HRV has been successfully used to screen people for possible referral to a Sleep Lab. Typically, an individual’s heart rate will vary the most while awake and then decrease at night during REM sleep.  In non-REM sleep, HRV will begin to decline as your heart rate slows down. In REM sleep, however, HRV begins to pick back up again because it is a very active time for the body and you have a faster heart rate. 

Research has shown that an individual with a low HRV value may have a hard time transitioning from being awake to entering deep REM sleep because their nervous system won’t be able to relax between breaths. This may be one reason why those with a low HRV might have difficulty sleeping or even feel tired during the day. An individual with a high HRV will most likely have an easier time transitioning from wakefulness to sleep, and will also maintain their deep REM sleep throughout the night.

WHY IS HRV IMPORTANT

HRV is important in medicine today. HRV analysis is a recognized tool for the estimation of cardiac autonomic modulations.  Cardiac autonomic modulations refer to the changes of cardiac parasympathetic and sympathetic activity in response to variations in respiratory rates. Heart Rate Variability is the variability within your heart rate over time, which is also measured by taking an ECG recording.  It’s widely used nowadays for tracking health and is even a feature on common smartwatches. HRV has been used to predict mortality after a heart attack, among other things. 

HRV is used as a marker for physical and mental stress. How so? The parasympathetic nervous system lowers heart rate and controls the “rest and digest” function. The sympathetic nervous system raises the heart rate, dilates blood vessels to generate a fight or flight response which is particularly useful when dealing with stressful events. As HRV increases, your cardiac output decreases as you enter a state of parasympathetic dominance. For example, those with depression or Post Traumatic Stress Disorder have been found to have a lower HRV. Low HRV may indicate that the individual has a harder time recovering from daily stressors, which could ultimately lead to health issues if left untreated.

HRV may be able to give some insight into how stress has been affecting your mental and physical health. If an individual is having a hard time maintaining good cognitive function, HRV can be used as a gauge to determine whether that person needs more rest or if they need to take time off from work. In the case of those who have anxiety or depression, low HRV may be able to predict the likelihood of an individual experiencing issues with their mental health.

Generally, a low HRV is linked with an increased risk of death and cardiovascular disease. By taking HRV to heart, individuals are able to get a better picture of their health. There are also times when high HRV may indicate that the person’s body is not operating at its best. An example of this would be an individual who does workouts that are too intense for them to handle. 

INCREASING YOUR HRV

When a person is in a stressful situation, their sympathetic nervous system takes over and an increased amount of cortisol will be released. This leads to a lower HRV which signals the body that there is stress present.

In response, one can attempt to reverse this effect by breathing slowly and deeply while engaging in relaxation techniques such as meditation or yoga. People who have a high HRV have been shown to have higher levels of a neurotransmitter called GABA, which is naturally released when a person is present in a relaxed environment.

Increasing your HRV will also increase the amount of energy that your body uses as it requires less energy from cortisol and adrenaline for this process. This leads to better blood pressure, weight management, performance under stress, and other optimal outcomes.

Just like you may use smart technology to count your steps, tracking HRV may be a useful tool to motivate behavioral and lifestyle change. For example, Sleep HRV measurements can provide insight on how you rate compared to other users in similar age groups. While HRV biometric tracking is still a new concept, I am hopeful it will help patients be more participatory in their health journey. 

Disclaimer: The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Additionally, the information provided in this blog, including but not limited to, text, graphics, images, and other material contained on this website, or in any linked materials, including but not limited to, text, graphics, images are not intended and should not be construed as medical advice and are for informational purposes only and should not be construed as medical advice. Always seek the advice of your physician or another qualified health provider with any questions you may have regarding a medical condition. Before taking any medications, over-the-counter drugs, supplements or herbs, consult a physician for a thorough evaluation. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition or treatment and before undertaking a new health care regimen, and never disregard professional medical advice or delay in seeking it because of something you have read on this or any website.

References

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3225923/

https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep

https://pubmed.ncbi.nlm.nih.gov/21658979/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7680518/

https://pubmed.ncbi.nlm.nih.gov/27918706/

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