Heart rate variability biofeedback as resilience development

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Heart Rate Variability Biofeedback

Chapter One: Introduction
By empowering individuals to take control of their own physiological processes through the conscientious application of basic exercises such as breathing and meditation, health care providers can engage in preventive care that helps to improve the overall condition of patients suffering from asthma, anxiety, depression and many other health issues (Lehrer, 2007; Kaur, Huseby, Sharma et al., 2017). Sakakibara (2016) has found that breathing tools can assist patients to “modify cognitive processing of negative stimuli” (p. S40). These breathing tools are the basis of heart rate variability biofeedback therapy.
The phrase “heart rate variability” (HRV) describes the normal process wherein the amount of time that elapses between one heartbeat and the next is characterized by some degree of variability—i.e., there is no consistency in the pace of one’s breathing (Stolnick & Mostofsky, 2014). Biofeedback is the process of communicating physiological telemetric information about their breathing to individuals seeking to change their physiology (Gervitz, 2015). Heart rate variability biofeedback (HRVB) combines the process of HRV with the process of biofeedback. It has been found to be an effective tool in reducing stress (Gervitz, 2015), treating depression (Sakakibara, 2016), and controlling asthma (Kaur et al., 2017). The value of HRVB is that it can help individuals learn to relax their muscles through mental focus, concentration and similar exercises designed to put the individual consciously in control of the breathing process. By regulating their breathing patterns, patients can manage their bodies, and biofeedback provides the guidance they need to do so. The end result of this preventive practice is that patients become more resilient in the face of stressors that prior to had had negative effects on the individual. From this perspective, the aim of HRVB is to support the development of resilience, just as a vaccination can be said to do the same.
Purpose of the Study
This study provides a random effects meta-analysis of the relevant literature to date regarding a variety of clinical outcome measures that can be linked to resilience. As HRVB is a measure of resilience, this meta-analysis was necessary because there are very few studies on HRVB large enough to compare results to clinically significant treatments. Because of that absence, a closer examination of the available literature on the subject is warranted. This study examines multiple outcome measures among published literature and dissertations from databases and article references.
Importance of the Study
The mechanisms for resilience are myriad and while the medical community is aware of some of them, a lack of focus on HRVB indicates that it is not cognizant of all of them. To help fill this gap, the purpose of this study was to add to the current knowledge of resilience with regard to HRVB’s impact on the body. This meta-analysis provides a greater understanding of the manner in which HRVB can be used as a tool in strengthening a patient’s resilience to certain negative stimuli. Currently there is a need to assess the efficacy of HRVB, also known as Slow Paced Breathing, as a treatment intervention in various health conditions that can be utilized in preventive care.
Rationale in Support of the Study
The rationale in support for this study is the fact that many clinical outcome measures have been examined by researchers and can be linked to resilience. HRVB’s effectiveness in helping patients to control their breathing and regulate their bodies in the face of negative stimuli marks it as a tool that should be considered in the light of resilience-strengthening practices. The benefits of considering this relationship and examining it in more detail are made evident in this meta-analysis. As the effectiveness of HRVB is not entirely corroborated by the scientific community, this study aims to provide an analysis of the available evidence to show that HRVB can be useful in strengthening resilience.
The need for a meta-analysis of this nature is also because it combines smaller studies for greater power. Funding is currently lacking for phase III trials of behavioral interventions and there is no other way to evaluate the general effectiveness of behavioral or pyschophysiological therapies.






Chapter Two: Review of the Literature
Breathing techniques have been practiced by individuals throughout history and throughout various cultures as a means of regulating the body. Slow paced breathing is useful in reducing stress, as yogis have demonstrated, which Gervitz (2015) showed in a study on how breathing techniques can calm the nerves even in response to substantially painful stimuli. In Gervitz’s (2015) study, whenever a directive was given to a yogi to become calm and centered, the breathing patterns used by the yogi 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 a concept that has entered into the popular consciousness in the wake of the fitness “boom” of recent decades (McKenzie, 2013). It is popularly defined alternatively by the editors of Psychology Today as “that ineffable quality that allows some people to be knocked down by life and come back stronger than ever” or “the maintenance of positive adjustment under challenging conditions such that the organization emerges from those conditions strengthened and more resourceful” (Nilakant & Walker, 2014, p. 80). 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.” Even 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), which indicates the vitality inherent in the concept.
Taken together, these popular definitions all serve to reinforce the notion that resilience is one of the most important ideas not just in culture but also in medicine because it speaks to the overall aim of a healthy body: the ability to fight off anything that attacks it. A healthy body’s resilience to disease, sickness or other negative stimuli can serve as a measure of that body’s ability to operate effectively. A viral infection, for instance, may cause momentary problems for a person, but if the immune system is resilient, the trial will 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. The growing 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 
Heart rate variability biofeedback is a technique that can be used to help strengthen a body’s resilience (Gervitz, 2015). 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 apply a focused method of conscious regulation to effect the same outcome as that of the external medication. The advantage to this alternative therapeutic intervention is that the patient practicing HRVB does not have to rely upon external medication and is thus free to exert greater influence and control over his/her own body through this preventive care practice. The drawback to advocating this therapy 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 as being efficacious over a period of time and being an effective technique for building and sustaining resilience.
HRV is an Index for Resilience
Heart rate variability 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. In fact, HRV is 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 a bodily process that is affected by heart rate variability biofeedback (Lehrer, 2013).
The major role players in the coordination of this type of breathing 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. Conversely, decreases in blood pressure lead to the opposite reaction (i.e., an acceleration of the heart rate and a constriction of the blood vessels). In this regard, Lehrer (2013) demonstrated 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 to obtain more effective 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 primary purpose 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. In the meta-analytic review conducted for this study, numerous conditions were identified as being treated by applying the HRVB technique, including the following disorders:
· Asthma;
· Anxiety (Trait);
· Cognitive Dysfunction;
· Coronary Artery Disease;
· Depression;
· Emotional Disturbances;
· Hypertension;
· Insomnia;
· Menopausal Symptoms;
· PTSD;
· Stress;
· Substance use/craving;
· Cardiac Conditions; and,
· 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 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 a corresponding decrease in blood pressure. 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. Heart rate typically accelerates when breathing in and decelerates when breathing out, resulting in 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 the body when it is attacked by stressors. Heart rate variability biofeedback/Slow Paced Breathing techniques allow individuals to assume control of the body’s most automatic functions. In a way, the process is analogous to switching off the autopilot in a jet airliner and putting the captain at the controls. In a case where the flight has hit turbulence, for example, the captain can moderate and modulate the flight by taking direct action. Likewise, people can do the same with their bodies when the nervous system has come into contact with stressors that are placing some type of pressure on the body.
The method of engaging with the body’s nervous system and consciously conducting the breathing process is the essence of the HRVB technique. The HRVB/Slow Paced Breathing technique allows the individual to gain and maintain 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 in a process that uses the types of negative feedback loops that are characteristic of Systems Theory as discussed below.
Systems Theory and Negative Feedback Loops
Systems Theory has wide applicability and this theoretical model has been used in numerous fields—from psychology to biology to sociology (Lehrer, 2013). Systems Theory in fact grew out of a mathematical approach developed by Wiener in the 1940s through seminal work on antiaircraft systems during World War II, suggesting that the analogy of the body being like an aircraft is especially relevant. The theory focuses on the way in which negative feedback loops, oscillations and control all work together within a system to maintain a desired state (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, p. 90). In addition, viable systems are entities that cannot be broken up into their characteristic constituent elements but must rather be taken as a whole (Lehrer, 2013). Likewise, negative feedback has been defined as the “hallmark of homeostatic regulatory activity” (Lehrer, 2013, p. 90).
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 prominently in both biological and behavioral controls, from processes in cells to whole, functioning societies (Lehrer, 2013). Therefore, feedback loops, oscillations and control all play an important role in maintaining many bodily systems, including those described below.
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. In addition, 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 therefore evident in this case as well as others.
Measure of the Parasympathetic Function
One common autonomic testing term is the cardiovagal (Gibbons, Cheshire & Fife, 2014). In this application, the parasympathetic response is measured by way of the cardiac function that is controlled by the vagus nerve which in turn impacts the variability of the heart rate. Likewise, Zygmunt and Stanczyk (2010) have 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. Consequently, it is also important to understand how heart rate is controlled as discussed below.
Heart Rate Control
Heart rate is controlled by the autonomic nervous system’s two branches: (a) the sympathetic nervous system and (b) 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 (or other caffeinated beverages), anxiety, excitement, environment, etc.
Some typical exercises that are used to lower or steady the heart rate when it is affected by stressors such as these include meditation and slow breathing and this is where the idea of HRV originates: the practice of taking slow, deliberate, thoughtful and purposeful breaths that can help the body regain control of itself in the face of external stressors or those 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” (McEwen, 2000, p. 108). Furthermore, the research to date also suggests that systemic disorders such as cardiovascular disease are associated with hostility and depressive illness (McEwen, 2000). For the purposes of this analysis, 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 characterized by the ability to respond to environmental stressors and return the body to a state of normalcy, the ability is diminished in chronic cases. In chronic cases, resilience is repeatedly tried and can be broken just as in war where even massive walls may be destroyed through repeated use of a battering ram. Similarly, 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. In this regard, 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. (p. 70)
Allostatic overload is, in other words, what happens when the body is pushed past the point of resilience. Therefore, it is important for medical practitioners to determine the extent to which the allostatic load is under pressure. For this purpose, HRV provides a good measure of allostatic capacityas resilience and allostasis go hand-in-hand. Heart rate variability is known to improve baroreflex gain (Lehrer, 2007) and 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:
· It 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 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. 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 integral to 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 were 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, number of 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. 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 is 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:
Chapter Three provides a detailed explanation of the methodology employed in this study. Chapter Four examines the results of the study. Chapter Five gives recommendations for future research.
Chapter Three: Methodology
A literature search was performed using the databases PsychINFO and PubMed. The Search criteria entered within the databases were: “heart rate variability biofeedback” or “biofeedback and exp heart rate” or “hrvb” or “exp heart rate or sinus arrhythmia or cardiac coherence or paced breathing or voluntary control” and “exp heart rateor sinus arrhythmia or cardiac coherence or emwave or stresseraser”.
This search was performed for all articles, research papers, and grey literature up to July 5, 2016 and generated 313 articles from PsychINFO and 572 articles from PubMed. To establish inter-rater reliability, three reviewers independently performed a preliminary review that consisted of reading the abstracts of each of the total 885 articles to search for inclusion criteria. The inclusion criteria were: the use of HRVB or paced breathing (PB) at a rate of 5.5 – 6.5 breaths per minute (bpm), or .09 - .11 Hz, and as a sole treatment for any condition. The reviewers reconciled differences after their independent reviews, and eliminated 718 articles.
The remaining 167 articles were analyzed in a secondary review, where the articles were read in their entirety to screen for exclusion criteria. The exclusion criteria consisted of: studies reporting physiological effects of HRVB or PB that did not report changes in clinical condition or performance, studies that did not use the specified rates of breathing, studies that conducted heart-rate biofeedback but not heart rate variability biofeedback, studies with a small sample size (n<10), studies that did not specifically control for HRVB as an intervention (e.g., studies that compared HRVB + cognitive behavior therapy with a control condition), and studies that did not have enough or usable data for calculating effect size. After the secondary review, 117 articles were excluded.
The meta analysis was performed using the Comprehensive Meta Analysis (CMA) program (Borenstein, Hedges, Higgins & Rothstein, 2005). A total of 50 articles were entered into the CMA program. Tallies were made for the study name and year of publication, comparisons made (e.g., HRVB vs. control, PB vs. control, HRVB vs. PB, etc.), outcome measures, time points at which data were collected, data format (e.g.,. means and standard deviations), pre- and post-study mean, standard deviation, and sample size in the treatment and control groups for each outcome measure, A conservative assumption was made that the correlation between pretest and post test measures in each group was r = 0.3 if not specified within the study). Also tallied were the type of treatment received (HRVB or PB), the number of weeks spanning the beginning to the end of the study, number of treatment sessions, type of control used (specific procedures such as relaxation, waiting list, etc. and broad categories of active or treatment as usual, or TAU), treatment description (e.g.. HRVB or HRVB + another treatment, such as medication or cognitive behavior therapy),, type of measure (ex self-reported, physiological), measure direction (positive or negative), and the specific problem category or health condition being treated. Table 1 shows categories used.
An individual row was added for each outcome measure within each study. A total of 50 studies generated 276 rows of usable data that was analyzed using the CMA program. Various health conditions were analyzed, as well as the various outcome measures used to assess them. The CMA program calculated the effect size for each outcome measure. Analyses were done using the average of the effect sizes for all outcome measures in each study and the results that emerged are presented in Chapter Four.

Chapter Four: Results
Included Studies and Study Characteristics
Initial search strategies produced 885 potential abstracts/citations, with 167 abstracts/citations being retrieved for a detailed review. Inclusion criteria was the use of heart rate variability biofeedback and paced breathing at a rate of about 6 breathes per minute (bpm), and that it was the sole treatment for any condition.
Treatment effects of HRVB
As seen in Figure 1, a random effects meta-analysis (including the outliers) identified a moderate treatment effect of HRVB compared to control conditions (Hedges G= .481, z= 7.50, p < 0.001). Visual inspection of the forest plot as seen in Figure 2, Q statistic, and I2 statistic identified the presence of moderate but significant heterogeneity across the studies (Q=94.3, p < .0001, I2= 46.98%). Using the Tau score, an individual given HRVB has less than 95% chance of doing better than with a control condition (Tau= .297).
Given that Lehrer (2004) was the only study of HRVB for Asthma and primarily used physiological measures, the summary effect was calculated with this trial included to examine the effects of HRVB.