Heart Rate Variability
by Allison Deckel
Yoga East Teacher Training 2022

Heart rate variability (HRV) is a normal occurrence and refers to the slight fluctuations that your heartbeat makes based on the needs of your body at the time (Cleveland Clinic, 2021). Heart rate variability measures how well the autonomic nervous system is working. The autonomic nervous system is divided into the sympathetic (SNS) and parasympathetic (PNS) nervous system. When the body is stressed, the SNS contributes to what is known as the “fight or flight” response. The (PNS) (del parentheses)contribute to functions referred to as “rest and digest.” In summary, HRV measures the balance between the SNS and the PNS (American Psychological Association, 2018). The most accurate way to monitor HRV is with an electrocardiogram, also referred to as an ECG or EKG. This is a machine that measures the electrical activity of the heart. This is done in a medical facility where electrodes (small, plastic patches that stick to the skin) are placed at certain spots on the chest, arms, and legs and hooked up to the machine (John Hopkins Medicine, 2022).

Our respiratory system syncs with our heart through a process called respiratory sinus arrhythmia (RSA). When we inhale, we activate our sympathetic nervous system increasing our heart rate. When we exhale, we activate our parasympathetic nervous system, decreasing out heart rate. The more robust the system the more variation there is between heart rates. The higher the HRV is, the more effective we are at managing our reactions to upsetting events and thinking through our best responses in a calm manner. (Cleveland Clinic, 2021).

When the heart is unable to fluctuate in response to breathing, this will have a negative impact on how the body reacts to stress. Specifically, low heart rate variability increases the likelihood for medical illness such as heart disease and cancer, as well as psychological problems such as depression and Post Traumatic Stress Disorder (PTSD).  Low HRV makes it more difficult to manage emotions and think through how we want to respond in the most effective way to stressors (Van der Kolk, 2014).

What impacts heart rate variability? There is a growing body of influence that early childhood trauma changes the brain and leads to various poor health outcomes, including diminished HRV. The CDC-Kaiser Permanente adverse childhood experiences (ACE) study is one of the largest investigations of how early childhood trauma effects physical and mental health outcomes. The findings indicated that as the number of ACEs increase, the risk for health problems later in life also increase (CDC, 2021). In the book, The Body Keeps the Score, the author, Bessel Van Der Kolk, MD, outlines how repeated exposure to traumatic events causes an over stimulation of the Autonomic Nervous System (ANS), resulting in poor HRV.

Yoga has been shown to have positive effects on physical and emotional well-being. Understanding this, Dr. Bessel Van Der Kolk and his team at the Trauma Center in Boston, MA, decided to study if regular yoga practice increased heart rate variability specifically. They selected thirty-seven women with severe trauma histories who had tried traditional psychotherapy but had not received much improvement. Half of the women took the yoga class, while the other half participated in dialectical behavior therapy (DBT), which is a well-established type of therapy that focuses on mindfulness. Their classes consisted of breath work (pranayama) and classic poses, with an emphasis on mindfulness, or being aware of the sensations that are happening during class within the body and in the mind. The results indicated that HRV improved with the yoga participants and did not change with the other group. These findings motivated them to incorporate yoga class as a treatment modality at their trauma center.

There are many ways to help students connect with their breath in a yoga class. A commonly used technique that is simple and effective is coherent breathing. In coherent breathing, the goal is to bring awareness to, as well as, extend the length of the breath itself. Students take a comfortable seat, keeping a straight spine, and asked to inhale through the nose for 6 counts and exhale through the nose for 6 counts. One may have to start with 4 counts and with practice work up to the full 6 counts. This is usually done at the beginning of class to bring awareness throughout the practice (Verywell Mind, 2020).

In the journal, Applied Psychophysiology and Biofeedback, a comprehensive search of multiple databases was conducted and all studies that reported a measure of HRV associated with any yoga practice were included. Studies were categorized by the study design and type of yoga practice. A total of 59 studies were reviewed involving a total of 2358 participants. Most studies were performed in India on relatively small numbers of healthy male yoga practitioners during a single laboratory session. Of the reviewed studies, 15 were randomized controlled trials. The reviewed studies suggest that yoga can improve HRV. Regular yoga practitioners were also found to have increased vagal tone at rest compared to non-yoga practitioners. However, they were unable to draw any firm conclusions about yoga and HRV as most studies were of poor quality, with small sample sizes and insufficient reporting of study design and statistical methods. While there is convincing evidence that yoga does improve HRV, more quality studies are needed to state this definitively (Posadzki, Kuzdzal, Lee, & Ernst, 2015).  

References:

Heart Rate Variability (HRV). Cleveland Clinic, 2021, retrieved from http://my.clevelandclinic.org/health/symptoms/21773-heart-rate-variability-hrv

Stress effects on the body. American Psychological Association, 2018 retrieved from https://www.apa.org/topics/stress/body

Violence Prevention. Centers for Disease Control and Prevention, 2021 retrieved from

https://www.cdc.gov/violenceprevention/aces/about.html

Bessel Van Der Kolk, MD (2014). The Body Keeps the Score: Brain, Mind, and Body in the Healing of Trauma. Penguin Books.

Posadzki, P., Kuzdzal, A., Lee, MS., Ernst, E., 2015. Yoga for heart rate variability: A systematic review and meta-analysis of randomized controlled trials. Applied Psychophysiological Biofeedback, 40, 239-249.

Health. John Hopkins Medicine, 2022, retrieved from https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/electrocardiogram

An Overview of Coherent Breathing. Verywell Mind, 2020 retrieved from

https://www.verywellmind.com/an-overview-of-coherent-breathing-4178943