Vagus Nerve Stimulators tVNS Stimulators

What Is Heart Rate Variability?

Updated on September 6, 2022
Heart Rate Variabilty

What makes the heart rate and its variability very unique? Heart rate variability simply means the measure of the variation in the time interval between each heartbeat in milliseconds. These fluctuations are usually undetectable except with specialized devices. This measure can be a sign of your overall health and well-being. HRV measures how uneven your heartbeat is (1).

The variation is controlled acutely by metabolic processes, hormonal reactions, cognitive processes, and exercise. Contrary to what you might think, HRV isn’t the same as heart rate. Although you can have a sense of what it feels like when you check your pulse by taking deep breaths in and out. Heart rate variation is controlled by a part of the nervous system called the Autonomic nervous system. The ANS is in control of bodily functions like breathing, digestion, blood pressure, and heart rate. It is subdivided into two components.

1. Sympathetic nervous system
2. Parasympathetic nervous system

The brain continuously processes information in the hypothalamus. The autonomic nervous system sends signals to the hypothalamus which it then sends to other parts of the body for stimulation or relaxation. The parasympathetic nervous system is responsible for the rest and digestion system. Digestion enables the body to recover and power down after the sympathetic nervous system’s “fight and stimulation ”is over. The sympathetic stimulates heart stress hormone production, increases the heart's cardiac output and concentration rate, and decreases heart rate variations needed during mentally or physically stressful conditions. The heart rate variation occurs because the autonomic nervous system operates beyond our conscious control.

Even though the ANS impacts the rate at which the heart beats, the sinoatrial node (SA node) allows the heart to beat at its rhythm. The SA node is the natural pacemaker that controls the heart rate and keeps the heart beating 100 beats per minute (bpm). So, for example, if a person has a heart rate of 70 beats per minute(bpm), the average R-R interval would be 1 second but some R-R intervals maybe 0.9 seconds and others 0.13 seconds. The higher the value of your HRV, the better it is for your body to adapt to stressors and changes. When in bad shape due to respiratory illness, overtraining, lack of sleep, etc, your HRV is reduced. This indicates the body is having trouble maintaining homeostasis and adapting to changes in its internal environment. This signals you need to take measures and be balanced.

HRV estimates changes in autonomic inputs in the heart in place of the mean level of autonomic inputs. Withdrawal and saturating levels of the input to the heart can lead to diminished HRV (6). Very high variance can indicate diseases like atrial fibrillation which is the most common type of heart arrhythmia. On the other hand, low variance can indicate an increased bout of illness or stress.

When should HRV be measured?

It is important to measure your heart rate variation while at rest, not after any other activity or exercise that can remarkably influence your baseline HRV reading. Take the measurement a few more times every week and note the mean value.

What does Low Heart Rate Variability Mean?

When your HRV is low, it points to the fact that your body is expending too much time in fight-or-flight mode and isn’t bouncing back from stress. This could mean that you are overwhelmed, you’re falling sick, emotionally depleted or you have sleep apnea. Consistently having a low HRV has a higher chance of developing cardiovascular diseases, chronic pain, insomnia, and anxiety-related disorders. In this case, it is important to increase parasympathetic activity; that is, the rest-and-digest mode.

What does a High Heart Rate Variation Mean?

Healthy people with a high HRV tend to have improved blood pressure, pain tolerance, focus, breathing, access to calmness, performance, and resilience. The parasympathetic nervous system and vagus nerve are where you seek balance in an increased HRV and vagal tone.

Sleeping HRV

When sleeping, your heart rate slows to its resting stage while the muscles relax and the body’s temperature falls. But at deeper sleep stages, the resting heart rate drops to about 20-30%. Heart rate variability should be lower during sleep than when you’re awake.

HRV is more of a symptom of how well a person sleeps than how it affects their quality of sleep. Research has shown that a person's HRV records can be used to detect sleeping disorders. HRV data is also used to determine the effect sleep disorders have on daytime functioning. Any sleep disorders that affect your sleep capacity also impact your heart rate efficiency.

Why Is It Important To Check HRV?

Here are the following reasons why it’s important to check your heart rate variability (3):

⦁ To prevent illness - Having a low HRV point to the possibility of having a cardiovascular disease. Knowing this helps you to begin working on time to prevent the potential of developing congestive heart failure, ventricular tachycardia, or myocardial infarction.

⦁ To detect stress level - People who have low heart rate variability easily experience more stress compared to those who have high HRV as their cardiovascular system is in good condition. Checking your heart rate helps you understand how best to respond to stress.

⦁ It can pinpoint ANS imbalances - When you are relaxed, the difference between the heartbeats is high, but while in fight-or-flight mode, the heartbeats are usually low.

Factors that affect HRV

Genetically, a person’s overall HRV level can be affected, but here are some other core factors.

⦁ Age: As you grow older, your HRV reduces when compared to that of a younger person.

⦁ Disease: HRV is usually lower in people suffering from certain diseases when compared to healthy people. Some of them are Heart diseases; Chronic kidney disease; Liver cirrhosis; Psychiatric diseases (panic attacks, epilepsy, depression, post-traumatic stress disorders, personality disorder, anxiety disorder, panic attacks, and anorexia - HRV is shown to be reduced in people who worry more; poor survival in premature babies.

⦁ Lifestyle: Being sedentary, stressed, and eating a poor diet can significantly impact your HRV negatively. Choosing to live a lifestyle can improve your HRV.

⦁ Medications: The medication you use can greatly impact your HRV, such as beta-blockers.

⦁ Inflammation: when there’s a higher level of inflammation in the body it causes a difference in the HRV. Inflammation is an indication of a variety of conditions, eg. Diabetic neuropathy.

⦁ Pregnancy: Alterations of HRV occur in healthy pregnancies, as with pregnancies with gestational diabetes which gives lower HRV mean values.

Devices for Monitoring Heart Rate Variability

Several medical and fitness devices that use sensors to detect heartbeats are now available. These sensors are for examination of the heart (sound), blood pressure measurement, pulse oximetry, and electrocardiogram( ECG). An ECG is the most accurate device used to measure heart rate variability. This device provides a graph gotten from electrical signals sent from electrodes placed on your arms, chest, and legs. The ECG measures different electrical signals to ascertain the timing between your heartbeat and how fast it is. HRV is also called the R-R interval. The spike in the wave pattern is the ‘R’ phase of the heartbeat.

There are also wearables for your fingers, wrist, and ankles that can collect heart Rate Variation data. Engaging in HRV analysis and HRV awareness is a good motivator for behavioral change. Outside of an ECG, if you want the best reading of your HRV, chest strap heart monitors are the best way to go. They are more accurate than fingers or wrist. A good HRV score is relative to each person. HRV is a highly sensitive metric and responds uniquely to everyone.

What is a good HRV score?

By general guidelines, HRV values below 50 mean a person is unhealthy. 50-100 ms means a person’s health has been compromised and a value above 100 ms classifies you as healthy. Although HRV responds uniquely to everyone because it is highly sensitive, a person's normal could be abnormal for another person. These scores can pass as a baseline for a good HRV score. Frequently wearing a tracking device for a few weeks can help you determine your baseline HRV measurement.

How is HRV measured?

In understanding your heart rate variation data, the most important measurements to take note of are;

1. Interbeat intervals- the time between individual beats)
2. RMSSD- a measure of high-frequency HRV)
3. SDNN- Standard deviation of NN intervals
4. VLF - Very low-frequency band

The most important rule is that a greater high-frequency heart rate variation indicates higher digest activity and parasympathetic rest. While a greater low-frequency HRV means more fight or flight (sympathetic activity).

Why is HRV a sign of fitness?

Having a high heart rate variability means that your body is reactive to both sets of inputs, sympathetic and parasympathetic. It is a sign that your nervous system is balanced, and that your body is very capable of adapting to its environment and performing at its best.

Can Vagus Nerve Stimulation alter HRV?

The vagus nerve is the 10th cranial nerve in the body that carries many indicators from the organs to the brain. It majorly constitutes the parasympathetic nervous system and serves many internal body functions: immune response, digestion, control of mood, heart rate, and muscle sensations. Stimulating the vagus nerve simply sends mild and consistent electrical stimulation to help control the irregular electrical brain activity, being a special activator of the parasympathetic nervous system.

Studies have shown that activation of VNS changes the intricacy of heart rate variability differently during wakefulness and sleep. During sleep, the value of HRV increases, while at wakefulness, the Vagus nerve stimulation (VNS) decreases. (5). In conclusion, an increase in parasympathetic tone is associated with increased HRV even in the presence of decreased HR. Even though the vagus nerve activity is indirectly measured in some diseases, HRV is a clinical tool that assesses vagal activity, called vagal tone. When there’s an abnormal vagal tone, it is usually associated with conditions like heart failure, hypertension, and diabetes.

Ways to improve heart rate variability

1. Stay hydrated. Your level of hydration determines the amount of blood you have in your system. So, the more hydrated you are, the more effortlessly it supplies oxygen and nutrients with enough blood circulation. Drink enough water every day (5).

2. Get good, consistent sleep. It is not enough to get quality sleep, it’s also necessary to maintain a regular sleep schedule. Regular sleep pattern helps you have more deep sleep and REM, thus increasing your HRV and improving your cardiac rhythm.

3. Practice intentional breathing. Taking deep and controlled breaths has been shown to boost HRV and help fight stress, which can decrease HRV.

3. Get exposed to natural light. Biological processes that regulate energy levels, hormone synthesis, and sleep-wake times are triggered when you are under natural sunlight. Other benefits of getting natural light exposure include increased physical strength, increased vitamin D production which is essential for healthy immunity, and improved alertness and mood.

3. Taking cold showers. the practice of exposing your body to cold temperatures is called cold thermogenesis. The parasympathetic system (digest and rest) increases when your body adjusts to cold, while your sympathetic system (flight or fight) decreases. The vagus nerve is stimulated by exposing your body to ice baths and cold showers for brief periods. This Vagus nerve controls HRV and activates the parasympathetic branch of your ANS.

3. Regular Exercise. Regular exercise is one effective way to improve your Heart Rate Variation. Note that rigorous exercise in a short time can put the body under too much strain and lower HRV. So, ensure you do less strenuous exercises.

Others include
⦁ Avoiding excess alcoholic consumption
⦁ Eating more Whole Foods
⦁ Breathing slowly and deeply
⦁ Practicing meditation.

What is heart rate variability? 

HRV is the measure of the variation in the time interval between each heartbeat. This measure can be a sign of your overall health and well-being.

When should HRV be measured?

 It is important to measure your heart rate variation while at rest, not after any other activity or exercise that can remarkably influence your baseline HRV reading. Take the measurement a few more times, every week and note the mean value.

Is a higher HRV always better?

Yes! Having a high heart rate variability is generally considered an indicator of a healthy heart. Healthy people with a high HRV tend to have improved blood pressure, pain tolerance, focus, breathing, access to calmness, performance, and resilience.

How to improve heart rate variability?

⦁ Stay hydrated 
⦁ Practice intentional breathing by taking a deep and controlled breath to improve HRV
⦁ Get exposed to natural light.
⦁ Exercise regularly
⦁ Take a cold shower 
⦁ Get good and constant sleep





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