Heart rate variability biofeedback for building physiological resilience

Heart rate variability biofeedback (HRVB) has been shown to be a tool to reduce stress (Gervitz, 2015). Gervitz (2015) describes biofeedback as the feeding back of physiological information to a person who then attempts to change his or her physiology with regard to the results of the feedback. The idea is to help individuals learn to relax their muscles through focus and concentration of various methods. Individuals can control their bodies more than they may realize with a little direction and the help of biofeedback.

Breathing techniques are especially useful in reducing stress -- particularly slow breathing, as demonstrated by yogis with whom Gervitz (2015) worked in identifying ways to calm themselves. Whenever a directive was given to a yogi to become calm and centered, the breathing patterns always became extraordinarily slow. To test the effect of this slow breathing technique, one yogi went so far as to drive skewers through his tongue, neck and arm: the yogi remained calm the entire time and his breathing pattern of very slow, steady breaths never changed throughout the entire duration of the skewering. In effect, the yogi's breathing technique had made his body resilient to any type of external stress.

What is Resilience?

Resilience is defined by Psychology Today as "that ineffable quality that allows some people to be knocked down by life and come back stronger than ever." Merriam Webster describes the quality of resilience as "the capability of a strained body to recover its size and shape after deformation caused especially by compressive stress" and "an ability to recover from or adjust easily to misfortune or change." The New York Times has even offered its own definition of resilience, noting that the word is derived from the Latin for "to jump again" (Kaur, Huseby, Sharma, Bhavsar, Sgobba, Zhang, Lehrer, 2017).

Resilience is one of the most important concepts in medicine because it speaks to the overall aim of a health body capable of fighting off anything that attacks its immune system. A healthy body's resilience to disease and sickness is a body that is operating effectively. A viral infection, for instance, may cause momentary problems for a person, but if the immune system is resilient, the trial will likely soon be over.

In medical terms, resiliency is best described as the body's ability to bounce back after stress or to recover from things. Our interest in resilience, from a medical point of view is based on the fact that bodies undergo stress routinely: the immune system must work to fend off viral and bacterial invaders as well as keep the body running like a well-tuned engine. Just as a machine must be taken to the garage for service on a routine basis to avoid breaking down from neglect, our bodies must be routinely monitored and cared for so as to facilitate the quality of resilience.

Why HRVB for Resilience

HRVB is a technique that can be used to help build up a body's resilience. By using a breathing technique that focuses on controlling the heart rate and thus regulating the exchange of gas that passes through the body's airways, the individual can use a focused method of conscious regulation to effect the same outcome as that of the external medication. The advantage is that the patient practicing HRVB does not have to rely upon the external medication and is thus free to exert greater influence and control over his/her own body as a result. The disadvantage is that the effectiveness of HRVB is not entirely corroborated by the scientific community and thus more studies need to be performed in order to evaluate its effectiveness. What evidence is available, however, points to HRVB being efficacious over a period of time and being an effective technique for supporting resilience.

HRV is an Index for Resilience

Heart rate variability (HRV) can act as a measure of general resilience by reflecting multiple homeostatic reflexes. In various disease states, HRV (and resilience) are reduced. Poor resilience leads to poor performance. Thus, HRV may serve as an index for resilience.

HRV is, in fact, applicable as a resilience indicator across various health conditions, populations and outcome measures. The manner in which HRV operates as an indicator can best be understood by seeing how the heart rate impacts breathing regulation. As Lehrer (1997) has shown, heart rate generally accelerates when breathing in and decelerates when breathing out, heart rate and breathing in a synchronized state tends to result in respiratory sinus arrhythmia, which is positively associated with individual health levels. The ability to control the variability of the heart rate is also instrumental in the individual's ability to regulate stress as an extension of blood pressure levels rising and lowering. Gas exchange is also an outcome that is affected by heart rate variability biofeedback (Lehrer, 2013).

The major role players in the coordination of this exercise include the baroreflex and the baroreceptors. The former plays an essential role in the control of blood pressure and heart rate in individuals, while the latter operate as receivers of the signals of changes in blood pressure and enable a trigger response in the tone of the blood vessels that impacts heart rate. When blood pressure rises, heart rate decelerates and vascular dilation takes place. Decreases in blood pressure lead to the opposite reaction -- i.e., an acceleration of the heart rate and a constriction of the blood vessels. Lehrer (2013) has shown that the baroreflex can be measured by identifying the heart rate's change for every 1 millimeter of alteration in blood pressure. HRVB in this light has been shown to be a particularly effective technique for stimulating the baroreflex and enabling a person better obtain control of the body's functions.

When an individual inhales, heart rate accelerates; during exhalation, heart rate decelerates. This act is what is known as a naturally occurring regulatory phenomenon within the body. It is governed by the operation of the vagus nerve which impacts lung and heart activity. The process is defined as respiratory sinus arrhythmia (RSA) and the exchange of gas through the action of inhaling/exhaling is the main goal of RSA. Regulating the heart rate during the process of inhalation and exhalation is integral to establishing a flow of control of the airways through which the gas exchange is conducted.

Knowing Some but Not All of the Mechanisms for Resilience

The mechanisms for resilience are myriad -- and the medical community is aware of some of them, but not all of them. The purpose of this study is to add to our knowledge of resilience with regard to HRVB's impact on the body. In the meta-analytic review conducted for this study, numerous conditions were found to be treated by applying the HRVB technique:

• Asthma

• Anxiety (Trait)

• Cognitive Dysfunction

• Coronary Artery Disease

• Depression

• Emotional Disturbances

• Hypertension

• Insomnia

• Menopausal Symptoms

• PTSD

• Stress

• Substance use/craving

• Cardiac Conditions

• Gastric Conditions

The meta-analysis was conducted to provide a greater understanding of the manner in which HRVB can be used effectively as a tool in strengthening resilience. Currently there is a need to assess the efficacy of HRVB/Slow Paced Breathing as a treatment intervention in various health conditions. The reason for the review is that many clinical outcome measures have been studied and can be linked to resilience.

Several of the Reflexes have Modulatory Functions

The baroreflex is one such example of the reflexes that have modulatory functions. The baroreflex gives a quick negative feedback loop that allows an elevated blood pressure to reflexively bring the heart rate down, which leads to the blood pressure decreasing. The decrease in the blood pressure causes the baroreflex activity to decrease, which in turn allows the heart rate to elevate and bring blood pressure levels back up to normal. This is the body's way of regulating itself.

Respiratory sinus arrhythmia itself is a heart rate variability that syncs with respiration and can be defined as a modulatory activity. As one's heart rate typically accelerates when breathing in and decelerates when breathing out, a synchronization of heart rate and breathing results in respiratory sinus arrhythmia, which is positively associated with individual health levels (Lehrer, 1997).

HRVB has a significant role in modulating the process of breathing and controlling one's body when it is attacked by stressors. HRVB/Slow Paced Breathing techniques allow the individual to assume the controls of the body's most automatic functions: in a way, it is like switching off the autopilot in a jet airliner and putting the captain at the controls. In a case where the flight has hit turbulence, the captain can moderate and modulate the flight by taking direct action. A person can do the same with his or her body when the nervous system has come into contact with stressors that are putting pressure on the body.

The method of engaging with the body's nervous system and consciously conducting the breathing process is what HRVB lets the individual do. The HRVB/Slow Paced Breathing technique allows the individual to claim greater control over the breathing process and, just as the pilot does with the aircraft during turbulence, bring the body back to a steady position.

Systems Theory and Negative Feedback Loops

Lehrer (2013) has pointed out that Systems Theory has a wide applicability, having been used in numerous fields -- from psychology to biology to sociology. Systems Theory in fact grew out of a mathematical approach developed by Wiener in the 1940s through work on antiaircraft systems during WW2 (so the analogy of the body being like an aircraft is not so random). The theory focused on the way in which negative feedback loops, oscillations and control all work together within a system (Lehrer, 2013).

What is a system? A system has been defined as "a variety of elements that interact with one another to form a whole entity" (Lehrer, 2013). It is an entity that cannot be broken up into characteristics but most be taken as a whole.

Negative feedback has been defined as the "hallmark of homeostatic regulatory activity" (Lehrer, 2013). The diverse systems that employ negative feedback loops all show the characteristic of oscillation. When oscillatory patterns emerge, it is the result of multiple feedback loops operating in conjunction with one another within a system. Oscillatory negative feedback loops all figure predominantly in both biological and behavioral controls, from processes in cells to whole, functioning societies (Lehrer, 2013).

Oxygen Metabolism and Parasympathetic Responses

As Gallego, Nsegbe and Durand (2001) have shown, the arterial pressure regulation feedback system provided by the relationship of carbon dioxide, oxygen and blood acid levels in effect is articulated via the metabolic control that is the breathing process. The parasympathetic response is essential in metabolizing oxygen and keeping the body in rhythm. Panneton (2013) has shown that parasympathetic responses are important in the body's regulation as well, especially with regard to the way in which the cardiovascular system assists in addressing the problem of anoxia:

A controlled reflex of onset bradycardia, a parasympathetic response, is foremost and reduces cardiac output dramatically, which by itself would induce a precipitous drop in arterial blood pressure. Thus the sympathetic nervous system counteracts the ensuing pressure drop, and a massive peripheral vasoconstriction commences redistributing circulating blood by reducing blood flow in cutaneous, muscular, and splanchnic circulations, but a maintained or augmented flow to the central nervous system and heart (Panneton, 2013, p. 284).

The interplay of the central nervous system and the breathing process is evident therefore in this case as well as others.

Measure of the Parasympathetic Function

Gibbons, Cheshire and Fife (2014) have shown that one common autonomic testing term is the cardiovagal. Here the parasympathetic response is measured by way of the cardiac function, which is controlled by the vagus nerve -- which in turn impacts the variability of the heart rate. Zygmunt and Stanczyk (2010) have also pointed out that "changes in heart rate during orthostatic testing and Valsalva manoeuvre, as well as during deep breathing or diving reflex, reflect parasympathetic modulation" (p. 11). Essentially, the cardiovascular system works because the vagal brake acts as a modulator: it is a restraint, as described by Dr. Stephen Porges in his Polyvagal Theory. As Porges (2001) has noted, the vagus places a limitation on the heart rate, though when vagal tone is taken away, rapid escalation of stress can result.

Heart Rate Control

Heart rate is controlled by the autonomic nervous system's two branches -- the sympathetic nervous system and the parasympathetic nervous system. The former produces hormones (epinephrine and norepinephrine) to boost heart rate, while the latter produces acetylcholine to decelerate heart rate. Heart rate can be impacted by various external factors, such as stress, coffee (caffeine), anxiety, excitement, environment, etc. Efforts to lower the heart rate or to steady it when it is impacted by stressors such as these include meditation and slow breathing. This is where the idea of HRV comes from -- the practice of taking slow, deliberate, thoughtful and purposeful breaths that can help the body to regain control of itself in the face of stressors that are external to it or that are part of the body's overall processes as a result of disease or infection. An example of how the heart is controlled by the body can be seen when one is engaging in exercise: when the body is actively moving in exercise, the sympathetic system actives and causes the heart rate to accelerate rapidly. The more that a person exercises, the more the heart itself is worked and the more the heart's actual size can even increase, just as a muscle in the arms or legs will increase when these particular parts of the body are used again and again regularly over a given period of time.

Allostasis

Allostasis (stability by variability) in stress research has received some attention over recent years. It plays a role with hormonal mediators in stress response as McEwen (2000) has shown. However, one of the challenges that researchers are uncovering is that the allostatic load center around the brain can be lead to impairment over time as environmental challenges trigger a continuation of stress for persons in certain instances where stressors are predominant factors of life: "In anxiety disorders, depressive illness, hostile and aggressive states, substance abuse, and post-traumatic stress disorder (PTSD), allostatic load takes the form of chemical imbalances as well as perturbations in the diurnal rhythm, and, in some cases, atrophy of brain structures. In addition, growing evidence indicates that depressive illness and hostility are both associated with cardiovascular disease (CVD) and other systemic disorders" (McEwen, 2000, p. 108). The allostatic load can be described as the wear and tear that a body undergoes over time as situations of chronic stress appear. The physiological consequence of long-term exposure to repeated stressors can lead to allostatic overload.

In terms of resilience, which is characterized by the ability to respond to environmental stressors and return the body to a state of normalcy. However, in chronic cases, resilience is repeatedly tried and can be broken, just as in war, a wall may be destroyed through repeated use of a battering ram. In the case of the body undergoing constant stress, the wall of resilience that it puts up to fend off the attacks of stressors can wear out eventually. Beaton and Simon (2011) note that one big event that is stressful in one's life can be enough to harm resilience -- just as in the case of modern warfare a battering ram is replaced by the use of explosives: one wall-shattering bomb will do the trick in bringing the wall (or one's resilience) down in tatters. Specifically, Beaton and Simon (2001) state that "traumatic early life experiences can shape the physiological stress response over development and are predictive of atypical hypothalamic -- pituitary -- adrenal (HPA) axis activation and neuroendocrine dysregulation" (p. 69). The rise of a traumatic event, however, is not necessary in contributing to allostatic overload, though it certainly can. Allostatic overload can occur as a result of continued stress over time on the body.

Allostatic Overload

The concept of allostatic overload is important to this study because it essentially equates to a decrease in HRV. Beaton and Simon (2011) highlight how allostatic overload can negatively impact the body:

Allostatic load is the physiological cost of maintaining homeostasis when faced with severe or chronic stress. Allostasis can occur via physiological (e.g., cortisol release or blood pressure elevation) or behavioral (e.g., avoiding stress-inducing stimuli) mechanisms that are elicited in response to real or perceived challenges. While modulated by individual differences in genotype, experience, and environment, allostatic load can increase over time to the point of overload and exhaustion. Allostatic overload exhausts coping resources and overexposes the organism to the hormonal, immunological, and neural mediators released via chronic activation and dysregulation of the HPA axis. Allostatic overload can also manifest as an inability to habituate to stressors, a failure to inhibit the stress response when not needed or as the lack of an effective stress response when one is truly needed.

Allostatic overload is, in other words, what happens when the body is pushed past the point of resilience. It is important for medical practitioners to be able to know the extent to which the allostatic load is under pressure. Fortunately, HRV is a good measure of allostatic capacity, as resilience and allostasis go hand in hand. HRV is known to improve baroreflex gain (Lehrer 2007) and huge acute effects on HRV can increase chronic variability over time.

The Reason for the Review

The reason for the review is that many clinical outcome measures have been studied and can be linked to resilience. As HRVB is a measure of resilience and what resilience is, the reason this meta-analysis review was conducted is that there were very few studies on HRVB that were large enough to compare to clinically significant treatments. Because of that absence, a closer examination of the available literature on the subject was warranted.

A total of 50 studies for the meta-analysis review were used after more than 800 articles generated from initial database searches were excluded based on criteria selected beforehand.

The need for meta-analysis can be summarized in the following three points, which highlight the impactful role that the method has on research:

• Combines smaller studies for greater power

• Funding is lacking for phase III trials of behavioral interventions

• There is no other way to evaluate general effectiveness of behavioral or psychophysiological therapies

First, meta-analysis allows researchers to combine smaller studies for greater power: this means that instead of focusing solely on one single study and being burdened by its limitations, multiple studies can be grouped together and the findings used to generate a wider sense of the predictability of outcomes based on the accumulated variables of each particular study.

Second, the fact that funding is lacking for phase III trials of behavioral interventions is a significant barrier to conducting further research in this important area of HRVB. In order to establish a better sense of why trials should move forward in this area, meta-analyses can be most helpful because they gather the existing pool of evidence into a single report that distills the data down to a clear and effectively communicated set of findings. In this manner, support for the proposed intervention can be gathered as a result of the convincing data and interpretations that are obtained through the meta-analysis.

Third, it is clear that there is no other way to evaluate the general effectiveness of behavioral or psychophysiological therapies without turning to meta-analysis review. The meta-analysis allows for a comprehensive and close look at the relevant literature available on the subject. As studies are meant to be reviewed and examined by professionals in the field, a meta-analysis enables practices and outcomes, trials and interventions to be assessed in side-by-side comparisons to see how certain approaches are treated and what the impact of certain variables are on the subject. When attempting to discover the usefulness of behavioral therapies, this approach is part and parcel of the discovery process.

The procedures involved in the meta-analysis included:

• Examining multiple outcome measures, often from the same study

• Focusing on primary and secondary measures

• Looking at published literature and dissertations

• Searching databases and references in articles

• Combining the measures and compute effect sizes

The process used in this meta-analysis was to include Cohen's d -- between-groups differences in mean changes divided by the pooled standard deviation. Cohen's d is based on sample averages and gives a biased estimate of the population effect size, particularly when small samples (fewer than 20) are used. This is why Cohen's d is often referred to as the uncorrected effect size. Hedge's g corrects this bias. Hedge's g was calculated using comprehensive meta-analysis software developed by Michael Borenstein. A forest plot and funnel plot were created to examine heterogeneity among the studies sampled in this review.

Cochrane criteria was found to be too rigorous: too few studies were available from the pool of HRVB literature to qualify for these standards. The process used in this study required randomization, selective reporting of significant findings in a study (including all primary and secondary measures). Elements that were not required for this study included criteria for concealment of group assignment, blinding of participants and personnel (since this is essentially impossible anyway in behavioral studies), blinding of assessment outcome (too few studies included this element), and missing data.

The meta-analysis review found that:

• HRVB has significantly greater effect size than either active or inactive controls

• No effects: active vs. inactive controls, # sessions or weeks, outcome variables, target conditions

• Without outliers, prediction interval is very strong: >95% chance that someone given HRVB will do better than people given a control condition

• The size of the improvement is not clinically significant as a sole treatment. But is an 8% improvement important?

The latter question does merit some consideration -- after all, statistical significance can become a barrier to breakthrough treatments in some cases. As the prediction interval is very strong, this meta-analysis shows that the evidence is there to suggest that HRVB is a practical and suitable treatment method.

More information on the precise nature of the assessment methodology will be provided in chapter 3 of this study, which focuses on methodology and explains what assessment techniques were used for this meta-analysis review. A breakdown of the rest of this study is as follows:

Chapters

The following chapters are included in this study:

Chapter 1 introduces the subject of the study and explains the background on HRVB, the concept of resilience, the rationale for the study, and gives a brief synopsis of the method used.

Chapter 2 provides a literature review that focuses on HRVB as a technique for effective treatment of a variety of ailments. It provides information on the 50 studies collected for the study and gives an overview of the relevant material.

Chapter 3 provides an examination of the methodology used in this study. This chapter gives more detail to the precise calculations used to assess the data obtained through the meta-analysis as well as on the search criteria and search method used to obtain the studies reviewed herein.

Chapter 4 provides the findings of the meta-analysis including numerous graphs and charts that give a visual representation of the evidence gathered through the assessments utilized, as described in the previous chapter.

Chapter 5 provides a discussion of the findings as well as recommendations for future research and a renewed call for the need for behavioral trials of the HRVB intervention so as to verify the efficacy of the technique that appears to be evident from the findings of the meta-analysis.

Conclusion

In conclusion, HRVB has been shown by what studies exist to be an effective technique in the treatment of stress that negatively impacts a body. While there are many variables that must be taken into consideration in terms of how a body deals with stress and how effectively breathing techniques can be used as an intervention with treating stress, it is important to note that there has been too little research conducted in this area to form a substantive or convincing opinion one way or another. The main purpose of this meta-analysis review, therefore, is to gather the relevant data that does exist on the topic of HRVB into one synthesized report and show how, through statistical analysis, it can be show to have at the very least an impact worth pursuing in study via clinical trials and assessments.

As the story of the yogi told by Gervitz (2015) shows, there is something to be said for the value of regulated breathing techniques and the calming effect it can have on the body. For bodies in the modern era that are loaded down with so much stress from so many places, it can be very important for patients to have access to a normal, natural and healthy technique that is not medicinal and that can be learned relatively easily. If such a technique can be shown to be able to have the same results on patients that it did on Gervitz's yogi, the practical implications for persons suffering from a variety of stressors could be enormous. Not only could it reduce patients' dependency on pharmacological interventions, which pose their own set of threats and dangers to the body, but the HRVB intervention could also be viewed as a positive way forward in the maintenance of a body's resilience for years to come. In short, HRVB could be just the type of care that care-worn patients are looking for in the 21st century.

References

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