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What Is Heart Rate Variability (HRV) And Why Does It Matter?


What Is Heart Rate Variability (HRV) And Why Does It Matter?

Heart rate variability (HRV) refers to the measure of the variations in the time interval between consecutive heartbeats.  These periods of time between successive heart beats are also known as RR intervals and is measured in milliseconds. This physiological phenomenon of variation in the time interval between heartbeats is controlled by the autonomic nervous system (ANS).

The heart may seem to beat evenly but the time between the heart beats can vary by milliseconds.   The amount of time variations between heartbeats varying very slightly in a fraction of a second and are detectable only with specialized devices. 

Every person has their own distinctive heart rate variability.  A person’s HRV may vary day to day and from season to season, and may also vary with age, gender and circadian rhythm.

Heart beat variations can be an indication of health problems such as heart conditions and mental health issues like anxiety and depression.


What Is The Difference Between Heart Rate And HRV?

Heart rate variability is not the same as a heart rate. Heart rate indicates how many times a person’s heart beats in each minute and is measured as beats per minute (bpm).

HRV indicates the time interval between two adjacent heartbeats and measured in milliseconds (ms).  

If a person’s heart rate is 60 beats per minute, the heart does not beat evenly once every second. Within that minute the time interval between two heart beats may be 1.15 seconds, whereas the next two heart beats may occur at an interval of 0.9 seconds. Greater the heart rate variability, greater is the body’s readiness to execute at a high level.


What Controls The Heart Rate Variability?

The autonomic nervous system (ANS) controls the heart rate variability in a person.

The hypothalamus, which is located above the brain stem, continuously process information from the sense organs and transmit the signals to the rest of the body through the ANS. 

The ANS operates on its own without a person’s conscious thinking even when a person is asleep.  The ANS can either relax or stimulate different functions in the body, including HRV.  

ANS is divided into two parts, the sympathetic nervous system and parasympathetic nervous system.

  • Sympathetic Nervous System: It increases the heart rate and blood pressure in an emergency situation causing fight-or-flight response.  The fight-or-flight response stimulates the heart to speed up, reducing time interval between consecutive heart beats causing lower HRV.
  • Parasympathetic Nervous System: The parasympathetic nervous system is responsible for the relaxation response which helps the body to recover, rest and digest. It balances the sympathetic nervous system and controls the normal relaxation response, especially after a fight-or-flight response. The relaxation response helps the heart to slow down, increasing time interval between consecutive heart beats causing higher HRV.

The autonomic nervous system helps to keep the body in balance and respond effectively during stress, unhealthy diet, poor sleep, isolation, dysfunctional relationships, overtraining or lack of exercise.   When these conditions occur chronically the ANS goes off-balance and HRV is affected.

Though the ANS affects the rate at which the heart beats, rhythmic heart beat occurs due to the Sinoatrial node (SA node) which is the natural pacemaker in the body that controls the heart rate. The SA node helps to maintain the heart beat around 100 beats per minute. 


How Does Heart Rate Variability Work?

The Sympathetic nervous system and the parasympathetic nervous system work together to control the HRV. 

The heart beats constantly at a specific rate. That heart rate becomes variable (HRV) depending on what a person is doing at a particular time and respiration and the needs of the body.

The heart rate slows down when a person is relaxed or is resting. The heart rate increases and becomes faster when a person is stressed, is in danger or involved in an active activity. 

When a person is in danger or is anxious, scared or startled, the sympathetic nervous system kicks in and stimulates the fight-or-flight response. The body releases adrenaline to react faster. The heart rate increases to meet the need of more blood and oxygen by the muscles.

Once the situation that put the body into fight-or-flight mode is over, the parasympathetic nervous system takes over. It controls the heart rate slowing it down, lowers blood pressure and signals the various systems of the body to relax or function normally.

When the body is in fight-or-flight mode, the difference between heartbeats is low as compared to when a person is in a relaxed mode where the difference between the heartbeats is high. 


What are the Benefits of Checking Heart Rate Variability?

Heart Rate

Checking heart rate variability can help identify many health conditions such as:

  • Detect reaction to emotions and environment: When the HRV is checked it can tell how a person is reacting to the environment, feelings and emotions. 
  • Detect stress levels: People with low HRV easily experience acute stress while people with high HRV rarely experience stress and their cardiovascular system is in good condition. Checking HRV can help to people to understand what stress factors are present in their life and how to better cope with them in a healthier way.  For example, if HRV is low it may be an indication that rest is required.
  • Have better understanding: Helps to gain better understanding of a person’s mental health, nutrition, risk of disease, sleep and warnings signs of sickness. If the daily routine remains the same, but HRV decreases, it may be an indicator of increased stress or oncoming illness.
  • Identify ANS imbalances:  The autonomic nervous system keeps the body in balance. ANS imbalance is an indicator of overall stress or poor health.
  • Increases awareness of lifestyle habits: Checking HRV helps to know if a person’s lifestyle habits are healthy or unhealthy for the heart. It can help to motivate behavioral change. 
  • Increases self-awareness: HRV measure can help increase self-awareness of how a person lives and thinks, and how their behavior affects their nervous system and bodily functions.


How to Check Heart Rate Variability?

The variations in heart rate are very small in milliseconds, hence it requires specialized devices to detect them.  Heart rate variability can be checked by using:

  • Electrocardiogram (ECG or EKG):   An electrocardiogram machine is used in a medical setting, to detect the heart rate variability.  This device, measures the electrical activity of the heart using sensors attached to the chest to monitor a person’s HRV.  Performed in a medical setting, this gives the most accurate measurement of HRV.
  • Chest strap heart monitors: Healthcare providers send the patient home after fixing chest strap heart monitors, that tracks the heart rate variability continuously for a longer period of time. The duration of time that a person’s heart rate variability is monitored can vary from a few minutes to 24 hours. Longer monitoring duration provided better information.  
  • Apps and watch systems:   Several apps and watch devices have been launched over the years that can check HRV.  However, the accuracy of these varies widely and they are not as dependable as chest strap heart monitors or an electrocardiogram.  Majority of wrist-worn fitness devices track the heart rate through the skin  and are usually not sensitive enough to detect heart rate variability accurately.


Why Does Heart Rate Variability Matter?

In a normal healthy body, HRV increases during relaxing activities such as sleep or meditation when the parasympathetic nervous system would dominate.

However, on the other hand, HRV decreases during stress when raised sympathetic activity triggers the body to keep up with the demand.

Thus, HRV is higher when the heart is beating slowly and lower when the heart beats faster during stress or exercise.

The HRV level changes from day to day, depending on the activity and amount of stress.  If a person is frequently stressed or burdened physically or mentally the normal interaction between the two nervous systems can be disrupted and the body can get caught in a sympathetically dominant fight state. This causes low HRV and high stress levels, even when the person is resting. This can be overwhelming on the body leading to several mental and physical health problems.


What’s A Good Heart Rate Variability Number?

The heart rate variability of a person can show how well the body is able to adapt to where a person is and to what they’re doing.

  • Low HRV

Lower HRV with fewer variations between heartbeats may mean that the sympathetic nervous system or the fight-or-flight response is activated. This condition may be triggered by negative situations, such as lack of sleep or stress.

Low HRV is a sign of current or future health problems because it shows that the body is less resilient and struggles to handle changing situations. Low HRV may indicate poor health that could contribute to some cardiovascular diseases or mental health problems such as anxiety and depression.  It can be a sign of stress, illness, poor sleep, overtraining. Low HRV is also common in people who have higher resting heart rates, because when the heart is beating faster, there is less time between beats reducing variability. Low HRV often occurs in physical health conditions like asthma, diabetes, heart arrhythmia, high blood pressure, high intensity exercise and mental health conditions like anxiety and depression.   Low HRV can be predictor of risk after a heart attack and can also be an early warning sign of diabetic neuropathy.

  • High HRV

When the heart rate variability is high, it indicates that a person’s nervous system is balanced and that the body is capable of adapting to the environment and functions at its best.

High HRV may occur when the parasympathetic nervous system or relaxation response is more dominating, resulting in decreased time between heartbeats. If the heart rate is highly variable it is evidence that the body can adapt to many kinds of changes. High HRV indicates better cardiovascular health, general fitness and the ability of a person to cope better under stressful situations.

Higher HRV is generally considered as an indicator of a healthy heart.  Studies show that higher HRV has been associated with reduced morbidity and mortality rates. People with HRV are usually less stressed, happier, have improved psychological well-being and better quality of life.


Is An Abnormal Heart Rate Variability Something That Should Make A Person Worry?

An abnormal heart rate variability will not usually cause a medical emergency, but it could be a sign of current health problems or an early warning sign that problems may occur in near future.

Most of the consumer-level devices such as watches or Apps that track heart rate variability are not as sensitive as an EKG and the information received may not be conclusive. A healthcare provider is the most qualified to look at a person’s heart rate and advise on what and should do about improving HRV.


Factors Which Influence-heart-rate Variability

There are many factors which influence the Heart Rate Variability including:

  • Physiological factors: Physiological factors that can impact the heart rate and heart rate variability include age, gender, genetic factors and circadian rhythm.  HRV increases when is person is sleeping and decreases in the hours just before waking up.  Heart rate variability also tends to normally decrease as a person gets older.
  • Diseases: Many studies show that HRV is lower in people who were suffering from certain diseases as compared to healthy people. Some of the diseases that lower HRV include: 
  • Diabetes
  • Heart diseases
  • Lung diseases
  • Psychiatric diseases such as depression, anxiety disorder, panic attacks, epilepsy, anorexia, borderline personality disorder and posttraumatic stress disorders.
  • Renal diseases
  • Certain medications: Certain medications can affect the heart rate variability.
  • Certain medical devices: Certain medical devices such as pacemakers can affect heart rate variability.
  • Lifestyle factors:  Lifestyle factors which influence HRV include:
  • Alcohol consumption
  • Diet
  • Medications
  • Physical activity,
  • Sleep
  • Stress
  • Tobacco use
  • External factors: Several external factors that can influence heart rate variability include:
    • Climate: Heat reduces HRV. However, exposure to cold doesn't affect HRV.
    • Exposure to noise lowers HRV.
    • Induced pain lowers HRV.


How to Improve Heart Rate Variability?

If a person’s heart rate variability is low, it can be improved in different ways. Methods of improving HRV include the following:

  • Active Lifestyle: People who have a high level of physical fitness and lead an active lifestyle can achieve an increase in parasympathetic activity and thus an increase their HRV.  
  • Adequate Sleep: The amount, quality and consistency of sleep a person gets affects HRV. Going to bed and waking up at regular time each day is beneficial.
  • Auto-Regulation: It is essential to get the body on a consistent routine particularly with regard to sleep and eating to align with circadian rhythm. The body performs things more efficiently when there is a regular routine.
  • Avoid Alcohol. One night of drinking can potentially lower HRV for up to five days. Avoiding alcohol would increase HRV.
  • Biofeedback Training: By controlling the breathing through biofeedback training, one can improve their heart rate variability. Research shows that biofeedback training can help improve levels of stress and anxiety thus improving HRV.
  • Cold Thermogenesis. Exposing the body for brief periods of time to cold temperatures such as cold showers, ice baths, etc. helps to stimulate the Vagus nerve which activates the parasympathetic branch of the autonomic nervous system and controls HRV.
  • Exercise and Train Appropriately: Intensive sports and overtraining can decrease HRV. Don’t push the body too hard for too many days without giving an opportunity to recover. Modifying the duration and intensity of physical training based on heart rate variability will help a person to train more efficiently.  With proper rest and recovery, the heart rate variability will rise.
  • Healthy Diet at the right time: Poor nutrition and eating at irregular times has harmful effects on HRV. Having a healthy diet and eating at the right time improves HRV.
  • Hydration: When a person is well hydrated it is easier for the blood to circulate and deliver oxygen and nutrients to the body. Drinking about one ounce of water per pound of bodyweight each day is ideal.
  • Intentional Breathing: Studies show that slow, controlled breathing techniques positively impacts HRV. They help to combat stress, which inhibits heart rate and reduce stress.
  • Lifestyle Changes: Making lifestyle changes such as regular exercise and stress management, mindfulness and meditation improves the overall health and the heart condition which can help improve heart rate variability.
  • Monitoring HRV: Monitoring and understanding how HRV varies over different points of time in response to different situations, would help to develop strategies for keeping calm under a wide range of circumstances.  
  • Natural Light Exposure. Going outdoors in the sunlight trigger biological processes that regulate sleep/wake times, energy levels, hormone production, improves mood, increases alertness and vitamin D production.
  • Take care of the mind: Mental health plays an important part in affecting the heart rate variability. If a person has mental health concerns like anxiety or depression, managing and reducing stress levels can improve a person’s heart rate variability.
  • Taking care of the body: Avoiding smoking, maintaining ideal weight, reducing weight/obesity would help in improving a person’s HRV.


PEMF And It’s Effects on Heart Rate Variability And Cardiovascular Health

 According to various studies, the therapeutic application of pulsed electromagnetic fields (PEMFs) can speed up bone fracture healing while also reducing pain. However, there are no objective criteria for determining the proper magnetic field strength or electromagnetic field type. Furthermore, only a few research have looked at the basic principles underlying the impact of electromagnetic fields on the human body. PEMFs have been demonstrated to affect cell activity, the autonomic nervous system, and blood flow in previous research. In stuies, when those exposed to higher magnetic field strengths, participants with lower baseline power recovered faster than those with higher power. Subjects' overall feelings of well-being were unaffected by the use of electromagnetic fields.

The described effects immediately faded as the magnetic field exposure was discontinued. On healthy participants, PEMF exposure showed a dose-dependent short-term effect. Following physical exertion, 20 minutes of exposure to PEMF resulted in a faster recovery of heart rate variability, particularly in the very low frequency range. The study also revealed that the subjects' VLF power had a moderating effect on their reaction to PEMF treatment. These findings have now been confirmed in a clinical investigation and should be considered when choosing a PEMF treatment.

The favorable therapeutic effects of specific non-ionising low-energy, time-varying electromagnetic fields (EMF) have been explored during the last few decades. This has resulted in a rise in the number of treatments for therapeutically refractory musculoskeletal diseases. Furthermore, a number of research have looked into the therapeutic effects of very low frequency pulse electromagnetic fields (ELF-PEMF) in the areas of insomnia, rapid bone repair and pain reduction, dental sensory and cutaneous pain. ELF-PEMF radiation has also been shown to aid wound healing in studies. A recent study [8] looked at the effects of ELF-PEMF radiation on the growth of the bacteria Staphylococcus aureus, which is important for infecting wound tissues. The results showed that all irradiated S. aureus bacteria grew at a slower rate than the control samples.

The effect of ELF-PEMF radiation on electrocardiogram (ECG) signals has been studied in several research studies. The effect of ELF-PEMF on heart rate variability (HRV) alterations (the low frequency (LF) and high frequency (HF) ratio), the effect of an intermittent exposure on heart rate (HR) and the effect on time interval parameters derived from the ECG wave, such as the duration of P and QRS waves have been studied. Several research have shown ELF-favorable EMF's therapeutic benefits, few have looked into its effect on ECG signal shape and time intervals. However, more research needs to be done on the same to more definitely conclude the benefits on the heart.