A healthy heartbeat still contains irregularities. For example, if your heart rate is 60 beats per minute, that does not mean that your heart beats once every second – or at one-second intervals like a clock. Rather, there is normal variation among the intervals between heartbeats. This per-beat variation is regulated by the nervous system and can even be felt at times: Place a finger gently on your neck and find your pulse. Normally you will notice that the longest interval takes place when you exhale, and the shortest interval occurs when you inhale. Heart rate variability measures how much variation there is in one’s heartbeat within a specific time frame. If the intervals between heartbeats are rather constant, this indicates that HRV is low. If the interval length varies, then HRV is high.
Understanding the autonomic nervous system
To understand HRV we must understand the autonomic nervous system (ANS) and its relationship to heart rate.
The autonomic nervous system regulates many important systems in the body, including heart rate, respiration rate and digestion. The autonomic nervous system has both a sympathetic (activation) and a parasympathetic (rest) branch. Heart rate variability is an indicator that both branches (the parasympathetic branch, in particular) are functioning. Factors such as stress can lead to overactivation or chronic activation of the sympathetic branch and decreased activation or even loss of the necessary braking activity of the parasympathetic branch. This imbalance in ANS activity will lead to elevated heart rate and lowered HRV, as it is the role of the parasympathetic nervous system to keep the nervous system in balance and promote longer inter-beat intervals and thus elevate HRV.
The role of stress
Stress plays a major role in the imbalance that can occur in the central nervous system. When the body and mind experience stress, an emotional sensor will activate the sympathetic nervous system (SNS). This is commonly referred to as the “fight or flight response.” If the parasympathetic nervous system does not engage to return the body to homeostasis and/or a sense of rest/digest then the result will be an unexpected release of adrenalin. Over time (and with chronic stress) this will lead to the breakdown of myocardial cells thus affecting blood flow to the heart.
To review, HRV is regulated by the nervous system and measuring heart rate variability gives the practitioner valuable information about the nervous system by indicating if the nervous system is functioning in a more sympathetic (or “fight or flight” state), or if it is operating in a more balanced state with the help of parasympathetic activation.
One of the biggest modern-day causes of HRV and thus nervous system disturbance is stress. In the February 2018 edition of Psychiatry Investigation, a study by Kim, Cheon, Bai, Lee and Koo entitled: “Stress and Heart Rate Variability: A Meta-analysis and Review of The Literature” concludes: “The current neurobiological evidence suggests that HRV is impacted by stress and supports its use for the objective assessment of psychological health and stress.”
Not only does the neurology of stress affect HRV and the heart, it can also affect other systems regulated by the nervous system like the immune and endocrine systems. In an article published in the March 2005 volume of Nature Reviews/Immunology by Ron Glaser and Janice Keicolt-Glaser entitled: “Stress Induced Immune Dysfunction: Implications for Health,” the complex relationship between the nervous system, the immune system and the endocrine system were reviewed. The authors demonstrate the impact of stress on the central nervous system (CNS) and its subsequent effects on various aspects of health. The following is a synopsis of their findings:
- Modulation of the immune response by the CNS is mediated by a complex network of bidirectional signals between the nervous, endocrine and immune system
- Communication between the CNS and the immune system is bidirectional
- Stressors can enhance the risk of developing infectious disease, and they can also prolong infectious illness episodes
- Studies of HIV-infected men have also indicated that stress increases the rate of disease progression
- Considerable anecdotal evidence has supported the relationship between psychological stress and the development, duration and recurrence of herpesvirus infections
- A case–control study indicated that psychological stress in healthy community-dwelling older adults was associated with the occurrence of herpes zoster
- Stress disrupts the production of pro-inflammatory cytokines that are important for wound healing, a mechanism that produces substantial delays in wound repair
- Chronic inflammation might be a contributing factor in up to 15 per cent of all cancer cases
- Stress-induced increases in the inflammatory response could be a broader pathway that links stress with cancer.
increased inflammation and increase susceptibility to frequent illness. Does this sound like any of your patients?
Wouldn’t it be wonderful to have a tool that could assess your patient’s neurophysiological balance? This tool could look at the relationship between the sympathetic and the parasympathetic nervous system of your patients and discover if they are living with their pedal to the metal (sympathetic dominance), or to see if their parasympathetic braking mechanism is (or isn’t) applying the brakes and balancing the system.
HRV is this valuable tool. Quick, easy to use, simple for the public to understand, and an excellent starting point for communicating the impact of stress on the spine, the nervous system and on health and well-being. Not only because it can offer a baseline assessment of where a patient is at when they come into your office, but more importantly, because it can be used to inform plans of management, predict response to care and in some cases ensure appropriate referral to necessary health professionals for high-risk individuals. There is no question that the use of HRV technology as part of the modern chiropractic practice has the potential to establish us once and for all as the leaders of the health and wellness industry that we have always been.
DR. DOUGLAS POOLEY graduated from the CMCC and has practiced in St. Thomas, Ont., for the past 39 years. He has represented the profession on national and provincial boards and has lectured nationally and internationally.
DR. KEITH THOMSON is both a chiropractor and a naturopathic doctor. He is a former president of the College of Chiropractors of Ontario. He has been in practice in Peterborough, Ont., for almost 40 years.