Did you think each heartbeat lasts the same length of time? Well it turns out, the duration of heartbeats vary. They vary in a predictable fashion: a sinusoidal one. In clinical biofeedback, we measure the instantaneous heart rate (IHR) of any given heartbeat. That is, we measure the duration of specific heartbeat and then calculate how many of those exact  heartbeats can fit into a minute to get that heartbeat’s IHR. We repeat this for every heartbeat. The IHR (any point along the curve above, each point representing a heartbeat’s heart rate) waxes and wanes in a sinusoidal fashion. This is called the HRV (HRV refers to the whole curve).
Generally, larger swings in HRV are desirable because they are associated with better health outcomes. It reflects the bodies ability to regulate itself cardiovascularly and psychophysiologically. (Khazan, 2013).   Cardiovascular Decreased HRV is associated with greater risk of mortality in patients who have: • Suffered a heart attack (Bigger et al., 1993) and in those with chronic coronary artery disease (Bigger et al., 1995). • High blood pressure (Schroeder et al., 2003) • Asthma: HRV biofeedback has been shown to drastically decrease asthma exacerbations, decrease asthma symptoms and medication use (Lehrer et al., 2004). • Cardiovascular illness is the cause of death in roughly 40% of North Americans and hypertension is the leading risk factor for cardiovascular disease. The FDA has deemed that biofeedback is a useful adjunct for managing hypertension.     Concussion neurological Neuropsychology Decreased HRV is associated with greater risk of • Diabetic neuropathy (Skinner et al., 2011) • Fibromyalgia (Cohen et al., 2000) • Anxiety (Friedman, 2007) • Panic disorder (Diveky et al., 2012) • Post-traumatic stress disorder (Tan et al., 2011) • Depression (Taylor, 2010). • Irritable Bowel Syndrome (Sowder et al, 2010).   This list above is not all inclusive, but have a glance at it again… Surely all of us have heard that all of these conditions can be caused by stress.     Does that mean that they are all psychiatric issues?   No. They are all mediated by the autonomic nervous system. Dysfunction of this system was discussed elsewhere on this website but suffice it to say that its effect is pervasive and instrumental to everything we do, every second of every day. Autonomic dysfunction can be potentiated by psychiatric conditions and vice versa. Although, to only address the psychiatric aspects at play – if present, consciously or subconsciously – and not address the physiological ones, may leave patients feeling unsatisfied and no different (Gevirtz, 2007).   In concussion, autonomic dysfunction is common. So are many of the conditions listed above, some more obviously than others, e.g., PTSD, depression, anxiety, etc. We have even seen a post-concussion patient present with labile blood pressure readings of over 190/110 despite having had perfectly controlled blood pressure prior to his concussion; no other changes to his health were identified.   The balance of our autonomic nervous system is reflected in the HRV. Biofeedback is a valuable tool to study and train HRV.
There are two processes that are represented in HRV.   1. The autonomic nervous system’s intrinsic balance   2. Regulatory reflexes     a. Respiratory sinus arrhythmia (RSA): refers to the variability in heart rate that corresponds to one’s breath; inhalation increases HRV, exhalation decreases HRV.     b. Heart rate component in the baroreflex system: When blood pressure rises, baroreceptors – which are pressure sensors in our arteries (the most important ones are in the carotid sinus and the aortic arch) are triggered, which causes the heart rate to fall, causing the blood pressure to fall. This in turn causes a rise in heart rate (again, via baroreceptors), which causes the blood pressure to rise. This cycles continues and tends to occur roughly at a rate of 5.5 cycles per minute.   The process we can affect most using biofeedback is the RSA. We use this as a flywheel to restoring balance to the autonomic nervous system and improving various emotional and physical symptoms caused by autonomic dysfunction (Gevirtz, Lehrer, & Schwartz, 2016). Porges (1995) and Gevirtz (2007) theorized that RSA is due to the activity of the vagus nerve. The vagus nerve is the 10th cranial nerve. It has parasympathetic branches that go to most organs (see Autonomic Dysfunction). The firing rate of this nerve is called the vagal tone. An increase in vagal tone causes a decrease in heart rate (i.e., during exhalation) and a decrease in vagal tone causes an increase in heart rate (i.e., during inhalation).   Some other therapies that are supplementary to biofeedback therapy are: CBT, CBT-insomnia, mindfulness, relaxation techniques, energy management, therapeutic activities, cardiovascular exercise, and general management of co-existing medical conditions (i.e., vestibular problems, visual problems).
This is done by educating patients how to maximize their HRV. If one is taught to breath with proper technique, and the ideal breathing rate (resonant frequency of breathing) is identified, we can maximize one’s HRV. This principle takes advantage of the interaction between the RSA and baroreceptor reflex.   Before we describe this, we will give an example: All of us have rocked someone on a swing before. We can all appreciate that there is a certain rhythm to pushing the person that will maximize the swing’s excursion; push a little too early and the swing slows down; push a little late and the swing also slows down; push a little too soft or even a little too hard, and the swing will slow down or buckle and slow down respectively. There is a way to swing someone that is just right: where your force and the person’s force meet at the right time in the right way.     This analogy lays out the principle that is at play in Resonance Frequency (RF) Training, the method used to train HRV maximization. We already established that on average the baroreflex tends to cause the heart rate to wax and wane in a sinusoidal fashion; and the cycle repeats itself about 5.5 times per minute – this exact figure varies between patients due to differences in anatomy and physiology. Now if we can train someone to effectively breathe at this same rate, the resonant frequency, we can get the swing a bit higher. That is, we already know that breathing causes the heart rate to ebb and flow in a sinusoidal fashion. If you get both, the baroreflex – over which we have no immediate control, like the child in the swing – and the RSA – over which we have control, like the person pushing the swing – to coincide just right, we can maximize the HRV (i.e., the excursion of the swing). This peak in HRV is known as “meditator’s peak,” as represents the most calm physiological state realized by experienced meditators.     Daily practice of resonant frequency training increases HRV, increases baroreflex gain, and improves pulmonary function, even in healthy individuals (Lehrer et al., 2003). These effects have been shown to persist even when resting, when not practicing resonant frequency breathing. Resonant frequency training also improves autonomic balance and one’s ability to regulate it (Lehrer et al., 2010). This training has been shown to impact the limbic system’s (in the brain a system of structures below the cerebrum) control over emotional reactivity (Gray et al., 2009).   There is a lot we still do not know about the benefits of HRV training using biofeedback. We know that the vagus nerve will send information to the brain and there is preliminary data showing that this mechanism can provide many new applications to resonant frequency training from areas like severe depression to seizures to autoimmune disorders.
It is interesting to note that many of the benefits linked to HRV training are similar to the ones linked to cardiovascular exercise. Cardiovascular exercise has also been found to be beneficial in heart patients, COPD and asthma patients, psychiatric patients, those with autonomic dysfunction, and in those with concussions.   An interesting observation: We sometimes assess healthy athletic individuals at rest for demonstrations. These are individuals who have never done resonant frequency training before. When assessing the individual, it surprises us that individual can hit their resonance frequency spot on without coaching proper breathing technique. In our experience, this is especially true of swimmers. Interestingly, many swimmers report that their asthma gets a lot better after having picked up swimming (You will remember studies have shown that HRV training can achieve the same result). Is this benefit due to the improved HRV that occurs with cardiovascular exercise?     We do know that HRV training promotes respiratory efficiency: increasing blood flow during inhalation when oxygen concentration in our lungs is at its highest (Yasuma & Hayano, 2004). We know that cardiovascular training also does promote this respiratory efficiency. Intuitively, we know that finding our groove in exercise or an efficient rhythm feels good.   There is a lot of work and research being done now and how to use information from HRV to adjust one’s training regimen to decrease the risk of injury and to increase performance.
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Research & writing: Dr. Taher Chugh

Last update: August 2018