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What Is Heart Rate Variability?

Medically Reviewed by Dan Brennan, MD on April 12, 2021

Heart rate variability {HRV) measures the difference in time between each heartbeat.

What Controls the Heart Rate Variability?

The autonomic nervous system (ANS) controls your HRV. The ANS, divided into two components, the sympathetic and the parasympathetic nervous system, regulates your heart rate, blood pressure, digestion, and breathing. These two components are referred to as the fight-or-flight system and the relaxation response.

The hypothalamus, a small region located above the brain stem, constantly process information and transmit signals to the rest of the body through the ANS. The signals can either relax or stimulate different functions in your body, including your HRV.  Depending on how you respond, especially in the case of constant negative signals, it can affect the functioning of your fight-or-flight response, forcing your heart rate into overdrive.

Although the ANS influences the rate at which your heart beats, the heart beats on its rhythm because of the Sinoatrial node (SA node), a natural pacemaker that controls the heart rate. The SA node keeps the heart beating around 100 beats per minute. 

The ANS affects the heart rhythm on a cellular level:  

  • The relaxation response tells your heart to slow down, making room for changes between beats (higher HRV)
  • Your brain's fight-or-flight system tells your heart to speed up, reducing space for change (lower HRV).

Why Check Heart Rate Variability?

  • It can identify ANS imbalances. When your system is in fight-or-flight mode, the difference between heartbeats is low as compared to when you are in a relaxed mode where the difference between the heartbeats is high. 
  • HRV can detect stress levels. People with low HRV can easily experience acute stress while people with high HRV rarely experience stress and their cardiovascular system is in great shape. Checking your HRV can help you understand how to respond to stress in a healthier way.
  • May increase awareness of your lifestyle habits. Checking your HRV is one way you can know if your lifestyle habits are healthy or unhealthy for your heart and a great tool to motivate behavioral change. 
  • It can detect your reaction to the environment, and emotions. Your nervous system can tell you how you are reacting to your environment, feelings, and emotions when you track your HRV. 
  • Can increase your self-awareness. HRV measurements can help increase your awareness of how you live and think, and how your behavior affects your nervous system and bodily functions.

Factors Influencing Heart Rate Variability

Physiological factors. Physiological factors that influence your heart rate and HRV include age, gender, and circadian rhythm. Your HRV must be taken into account in short time measurements ranging from a few minutes to a few hours. While you sleep your HRV increases and decreases significantly in the hours just before you wake up. 

Diseases. Many studies have examined the effects of various diseases on HRV. HRV was found to be lower in people who were suffering from certain diseases compared to healthy people. Some of these diseases include: 

  • Heart diseases
  • Lung diseases
  • Renal diseases (chronic kidney insufficiency)
  • Psychiatric diseases (anxiety disorder, panic attacks, posttraumatic stress disorders, epilepsy, anorexia, borderline personality disorder, and depression)

Diseases such as rheumatoid arthritis cause no clear changes in a person's HRV. People who maintain active lifestyles and a high level of physical fitness can achieve an increase in their basic parasympathetic activity and thus an increase in their HRV.  However, intensive sports, competitions, and overtraining syndrome can decrease HRV. Regular alcohol abuse for men and women can reduce HRV.

External factors. Several outside factors that can influence heart rate variability include:

  • Climate factors lead to changes in HRV due to the physiological reaction of the vegetative nervous system. Heat increases sympathetic nervous system activity, reducing HRV. Exposure to cold, however, doesn't affect HRV.
  • Exposure to noise leads to a decrease in HRV because it increases sympathetic nervous system activity.
  • Induced pain results in a lowering of HRV due to the activation of the physiological sympathetic nervous system.

How to Check Your Heart Rate Variability

  • Electrocardiogram. Special wires are attached to your chest to monitor your HRV.
  • Apps and watch systems. Various companies over the years have launched apps and heart rate watch systems that can help you check your HRV, although the accuracy of these methods is still undetermined. 
  • Chest strap heart monitors. If you want the most accurate reading of your HRV outside of an electrocardiogram, this is the best way to go. Chest strap heart monitors are more accurate than finger or wrist devices.
WebMD Medical Reference

Sources

SOURCES: 

Encyclopædia Britannica: "Cardiac muscle."

Harvard Health Publishing: “Heart rate variability: A new way to track well-being.”

International Cardiovascular Forum Journal: “Factors Influencing Heart Rate Variability.”

Neuroscientifically Challenged: “Know Your Brain: Hypothalamus.”‌‌‌

ScienceDirect: “Heart Rate Variability.”

University of California, San Francisco MacArthur Research Network on Socioeconomic Status and Health: “Heart Rate Variability.”

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