Heart Rate Variability: An Important Predictor of Health?
- Sep 5, 2023
- 6 min read
Our lives consist of constant fluctuations between "being revved up" (sympathetic, fight or flight activity) and working to "calm down" (parasympathetic, rest, recover, digest activity). As we are sleeping during the night, parasympathetic activity is high (as para is related to rest and recovery), but high levels of sympathetic activity are necessary in order to wake us up (this sympathetic activity is accomplished per the release of cortisol, our stress hormone, which is highest in the morning ). Overall, throughout the day, sympathetic activity will remain higher in order to allow us to be "revved up enough" to get through our daily activity. It will spike beyond a "normally elevated level" when we are physically or mentally stressed. Sympathetic activity then slowly decreases over the day's time and should be lowest at night, when parasympathetic activity must increase in order to allow sleep.
The Heart's Response: Heart Rate Variability
This process of fluctuating between "sympathetic fight or flight" and "parasympathetic rest, recover, and digest" continues all day long. These fluctuations are modulated by many things: circadian rhythms that control sleep and wake cycles, our daily demands, and inflammatory chemicals, to name a few. In response to these moves between sympathetic and parasympathetic activity (which are controlled by the nervous system), the heart must respond as well. When we are "revved up" with more sympathetic activity, the body releases adrenaline, which speeds up the rate of the heart so that it can deliver more oxygen and energy to the muscles and allow us to take action. When we need a more restful, parasympathetic response, the vagus nerve sends signals to slow down the rate of the heart, to decrease blood flow to the muscles, and to increase blood flow to areas like the gut, in order to promote good digestion. (This is why your mother told you you couldn't go swimming right after eating!)
So, depending on what we are doing, our nervous system is setting the tone in regard to a "fight or flight" or a "rest/relax/recover response", and our heart must be able to adapt to these changes quickly based on our needs in the moment. These cardiac adjustments can come in significant heart changes like how fast the heart is beating (heart rate), or how forcefully the heart is contracting (cardiac output), or they can come in very subtle changes to the rate of the heart. These subtle changes are referred to as heart rate variability (HRV). These can be changes in fractions of seconds in between heartbeats which are not easily detected but can be seen on and electrocardiogram (EKG) and with some biofeedback home monitoring devices (a biofeedback device gives feedback about the function and state of the body). A good heart rate variability means that the heart and nervous system are fine tuned so that they can seamlessly respond to changing needs and activities throughout the day. HRV is an indication of how well an individual can adapt and respond to stress. A good HRV not only means that the heart can subtly speed up when we need more of a "fight or flight response", but it also means that the heart can effectively slow down and recover when "fight or flight" is no longer appropriate.
Is Heart Rate Variability and Important Indicator of Health?
Traditionally, medicine has focused on indicators such as pulse rate, blood pressure, and cardiac output as the primary indicators of heart health. However, a great deal of current research indicates the HRV might also be a critical indicator of health, as it shows us how adaptive our nervous system and heart are in dealing with stress. While cardiac output is generally an indication of the strength of the heart, and blood pressure is an often an indication of the resistance in the vessels that the heart must pump against, good heart rate variability is an indication of "fine-tuned cardiac control." When the nervous system and the heart are working well together, the heart is able to subtly decrease the time in between beats when it is necessary to "rev things up", and just as easily, increase the time between beats in order to allow the heart to recover and minimize energy expenditure. (As an interesting aside which also drives home the importance of HRV, if your heart beats an average of 80 beats per minute, in a day's time, it will contract 115,200 times. If the heart was able to decrease to 79 beats per minute for half of your day, that decrease of one second (for only 12 hours) would spare the heart approximately 21,600 contractions per month!)
Conditions which can Impact Heart Rate Variability
1. Changes with Age:
Heart rate variability does change throughout the lifespan. This makes sense: a child can move between absolute rest and maximum cardiac output without difficulty and without any great risk to the heart. For a 75 yr old, those kind of rapid changes in demand are often what proceeds a cardiac event, as the heart has a greater difficulty in responding to changes in demand (stress) as we age.
2. Chronic pain:
One study examined over 600 individuals to explore the relationship between HRV and pain. The study monitored parasympathetic regulation of the heart, per EKG; evaluated pain and health behaviors; and tracked blood pressure and inflammatory markers (white blood cell count, C-reactive protein, and fibrinogen). The study found that regulation of heart rate by the vagus nerve ("down-regulation" or promotion of parasympathetic-rest-relax-digest-recover activity) was impaired in individuals with chronic pain. This impairment of vagus nerve activity obviously limited effective changes in heart rate variability. This research is consistent with countless research which indicates that chronic pain is associated with a preponderance of sympathetic versus parasympathetic activity. https://pubmed.ncbi.nlm.nih.gov/25924095/
A similar study showed that while individuals with chronic pain present with similar blood pressure responses as compared to the non-pain population, individuals with chronic pain demonstrate lower resting heart rate variability. In other words, in individuals with chronic pain, the parasympathetic nervous system is not as effective in making subtle changes to heart rate when at rest.
3. Chronic Fatigue (CFS):
"The majority of studies agree that there is an increase in heart rate in patients with CFS, at rest and under stress. " https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5772628/
"One study published in the journal Fatigue in 2016 reported a mean age of 58.8 years for deaths related to heart failure in people with ME/CFS. That's about 25 years younger than the mean age of cardiac-related death overall. While no one can know for sure which factors may have contributed to this result, some studies suggest that ME/CFS could be linked to insufficient heart function." The below-referenced article cites several heart irregularities noted in individuals with chronic fatigue, one of which is decreased heart rate variability during sleep.
4. Anxiety Disorder (AD)
An analysis of 99 studies (and over 4800 subjects) of individuals with anxiety indicated that "patients with AD had significantly lower resting-state HRV than the healthy population". In other words, individuals with anxiety demonstrated greater difficulty in making subtle heart rate modifications to slow the heart when at rest.
5. Depression:
The following study revealed significant differences in HRV between depressive patients and healthy controls. Further, the study found that as depressive symptoms improved, heart rate variability followed suit.
If you are interested in reading more about the basics of heart rate variability, check out the following article by the Cleveland Clinic. https://my.clevelandclinic.org/health/symptoms/21773-heart-rate-variability-hrv
Also look for more posts from Warriors for Wellness related to heart rate variability and other aspects of health! Or check out our individual coaching services and group education/activity classes: https://www.warriors4wellness.org/
Disclaimer: This BLOG is for Educational Purposes, Only. This information provided is educational and informational in nature and is made only as general information. The information does not establish a patient-provider relationship, establish a standard of care, or offer medical, dietary, or therapeutic care, advice, opinion, diagnosis, or treatment. This information does not replace independent professional or medical judgment and should not be relied upon as medical, psychological, or other professional advice of any kind or nature whatsoever. This information should not be used for diagnosing or treating any mental or physical health problem or disease. You are solely responsible for any action taken based on your interpretation of this information and you are responsible for your own health care decision-making by obtaining any necessary consultations with appropriately licensed health care professionals such as physicians and psychologists.
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