What Is Heart Rate Variability (HRV)? Normal, High, and Low

Your heart rate shows you how many times your heart beats in a minute, measured as beats per minute (bpm), whereas HRV shows you the time interval between two heartbeats, measured in milliseconds (ms). 

Although your heart rate may be 60 bpm, it does not mean that there has been a gap of one second between two heartbeats. One set of heartbeats may be at an interval of 1.3 seconds, whereas the next two may be at an interval of 0.7 seconds.

Your HRV is influenced by several physical and psychological factors and is an important parameter to measure whether your ANS is healthy or imbalanced. HRV may be monitored using a specialized continuous electrocardiogram (ECG) monitoring device or commonly available heart rate monitors.

• Physiological factors. Age, gender, genetic factors, and circadian rhythm can impact your heart rate and HRV.
• Lifestyle factors. These include diet, physical activity, stress, alcohol consumption, tobacco use, sleep, medications, etc.
• Diseases. Studies have shown that HRV is lower in people suffering from diseases such as:
  • Diabetes
  • Heart diseases
  • Lung diseases
  • Renal diseases (such as chronic kidney insufficiency)
  • Anxiety disorders, panic attacks, posttraumatic stress disorders, epilepsy, anorexia, and other psychiatric diseases
• External factors. Variables that can cause changes in HRV include climate, exposure to noise, and induced pain.

Low HRV may mean that your fight-or-flight response (sympathetic arm of the ANS) is dominating, leading to fewer variations between heartbeats. This may be triggered by negative situations, such as stress or lack of sleep. Low HRV may thus indicate poor health that can contribute to mental health problems such as depression and anxiety and even some cardiovascular diseases.

High HRV may occur when the relaxation response (parasympathetic arm of the ANS) is more activated, resulting in decreased time between heartbeats. This may be seen when you are relaxed. In this state, you have more flexibility and resilience in switching between low and high heart rates. High HRV may thus indicate better cardiovascular health and the ability to cope better with stressful situations.

If your HRV is low, you can take steps to improve your HRV through lifestyle habits such as regular exercise, stress management, adequate sleep, and healthy eating. 

Understanding and monitoring your HRV over different points of time can help you determine how your nervous system is responding to different situations, thus giving you the information you need to develop strategies for keeping calm and performing your best under a wide variety of circumstances.