HRV BIOFEEDBACK IN TREATMENT OF VARIOUS PATHOLOGICAL STATES AND DISORDERS
Heart Rate Variability Biofeedback, or HRV biofeedback, is a relatively new technique training human beings to change the variability and dominant rhythms in their heart activity. Recent research suggests an effectiveness of HRV biofeedback in the treatment of many medical and psychiatric conditions including: anxiety disorders, depression, asthma, chronic obstructive pulmonary disease, cardiovascular conditions, cardiac rehabilitation, hypertension, pregnancy-induced hypertension, irritable bowel syndrome, cyclic vomiting, chronic fatigue, recurrent abdominal pain, chronic muscle pain, fibromyalgia, PTSD, insomnia, and other autonomically mediated conditions and for optimal performance training.
As human beings age or suffer an illness, the total variability in heart rate is reduced, and the risk of illness and death increases. Several clinical findings show the importance of the changes in the rhythms of the heart. Decreased variability may predict sudden infant death. Lower variability in heart rate predicts a greater risk for further cardiac symptoms and death after a heart attack. Clinical depression also lowers heart rate variability and increases the risk of coronary artery disease. Heart rate variability has come to be regarded as a useful prognostic index or marker for morbidity and mortality.
Heart rate variability means the changes in the interval or distance between one beat of the heart and the next, as measured in milliseconds. The interbeat interval (IBI) is the time between one R wave (or heartbeat) and the next, in milliseconds. The IBI is highly variable within any given time period. HRV typically is quantified by measuring the interval between successive R-wave peaks (RR intervals) in the electrocardiogram (ECG).
Regular exercise increases heart rate variability. A scientific study of the variability in heart rate is fairly recent, and only in the past ten years did it become possible to train human beings to change the variability in heart rhythms, through biofeedback training. This cardiorespiratory intervention has subsequently been labeled HRV biofeedback, respiratory sinus arrhythmia (RSA) biofeedback, or resonance frequency feedback (RFF). The procedure of HRV biofeedback consists of feeding back the beat by beat heart rate data during slow breathing maneuvers such that the participant tries to maximize RSA.
PHYSIOLOGY OF HEART RATE VARIABILITY. BAROREFLEX.
People often breathe at differing frequencies at different states, and various individuals tend to breathe at different rates. For most people, most of the time, breathing frequency is between 0.15 and 0.4 Hz, or 9 to 24 breaths per minute. The technique of HRV Biofeedback involves learning to breathe at a resonance frequency of the cardiovascular system. Breathing at this frequency causes the heart rate to go up and down in phase with respiration. Heart rate increases with inhalation and decreases with exhalation. Then, respiratory gas exchange efficiency is maximized. Regular practice of this technique over a period of time has been shown to produce clinically significant improvement for a variety of disorders, including pain, asthma, anxiety, depression, chronic obstructive pulmonary disease, and hypertension.
People are able to produce very large increases in HRV through biofeedback because of ‘‘resonance’’ characteristics in the cardiovascular system. HRV biofeedback stimulates a particular reflex in the cardiovascular system that has a certain rhythm to it. It is called the ‘‘baroreflex’’ and it helps to control blood pressure. It also helps to control emotional reactivity and promotes breathing efficiency. The baroreflex is mediating through the nucleus tractus solitarius, located in the brainstem. This center communicates directly with the amygdala, a center for emotional control, in a pathway extending through the insula. Perhaps it is for this reason that various studies have shown positive HRV biofeedback effects for treating anxiety, phobias, and depression.
When blood pressure goes up, the baroreflex causes the heart rate to go down, and when blood pressure goes down, the heart rate goes up. This causes a rhythm in heart rate fluctuations. When a person breathes at this exact rhythm (which varies among people, generally between 4.5 and 6.5 times a minute), the baroreflex system resonates. How to find the frequency for each person at which the baroreflex system resonates? This will be the frequency that produces the biggest swings in heart rate between inhaling and exhaling. To find this frequency person should try to breathe at various rates per minute to find the exact frequency at which the cardiovascular system resonates. This will be his/her resonance breathing frequency. This frequency varied from individual to individual, but it is approximately 0.1 Hz or six breaths per minute. When people breathe at this frequency, the baroreflex system is stimulated and strengthened, and through projections to other systems in the body (e.g., inflammatory and limbic systems), other events occur that produce the many beneficial effects of HRV biofeedback.
Thus, breathing becomes a natural way to provide external stimulation to increase HRV. Conversely, each breath then stimulates the baroreflex. The baroreflex is a reflex mediated by blood pressure sensors called baroreceptors in the aorta and carotid artery that help modulate blood pressure fluctuations. Cardiopulmonary and blood pressure sensors (baroreceptors) detect respiratory changes in cardiac filling and arterial pressure. Baroreceptors in the walls of these arteries detect stretching of the arteries as blood pressure increases and signal to the Sinoatrial Node via the parasympathetic nervous system to slow down the heart. When blood pressure increases, the baroreflex causes immediate decreases in heart rate. As the blood pressure falls, the baroreflex causes immediate increases in heart rate through the sympathetic nervous system. The ability of blood pressure changes to regulate the heart rate is called the Baroreceptor Sensitivity.
PHYSIOLOGY OF HEART RATE VARIABILITY (HRV). AUTONOMIC NERVOUS SYSTEM
Although HRV is influenced by numerous physiological and environmental factors, two are particularly prominent and of psychophysiological importance: the influence of the Autonomic Nervous System (ANS) on cardiac activity and ANS regulation by the central autonomic network (CAN). The heart is innervated by the sympathetic and parasympathetic (vagal) branches of the ANS, which exert a regulatory influence on heart rate by influencing the activity of the primary pacemaker of the heart, the sinoatrial node.
The sinoatrial node generates action potentials that course throughout the cardiac tissue, causing regions of the myocardium (heart muscle) to contract in the orchestrated fashion that characterizes a heartbeat. Activation of sympathetic fibers has an excitatory influence on the firing rate of the sinoatrial node and results in increased heart rate. In contrast, parasympathetic activation has an inhibitory influence on the pacemaking activity of the sinoatrial node and produces a decreased heart rate. Alternatively, it can be said that the two autonomic branches regulate the lengths of time between consecutive heartbeats, or the interbeat intervals (IBI), with faster heart rates corresponding to shorter interbeat intervals and vice versa. The parasympathetic nervous system (PNS) and the sympathetic nervous system (SNS) act antagonistically to influence cardiac activity. For example, an increase in heart rate could arise from either increased sympathetic activity or decreased parasympathetic inhibition (vagal withdrawal).
During physical or psychological stress, the activity of the SNS becomes dominant, producing physiological arousal to aid in adapting to the challenge. An increased pulse, or heart rate, is characteristic of this state of arousal. During periods of relative safety and stability, the PNS is dominant and maintains a lower degree of physiological arousal and a decreased heart rate. The ease with which an individual can transition between high and low arousal states is dependent on the ability of the ANS to rapidly vary heart rate. A flexible ANS allows for rapid generation or modulation of physiological and emotional states in accordance with situational demands.
Sympathetic influence on heart rate is mediated by neurotransmission of norepinephrine and possesses a slow course of action on cardiac function. That is, changes in heart rate due to sympathetic activation unfold rather slowly, with peak effect observed after about 4 s and return to baseline after about 20 s. In contrast, parasympathetic regulation of the heart is mediated by acetylcholine neurotransmission and has a very short latency of response, with a peak effect at about 0.5 s and return to baseline within 1 s. The ability of the PNS to rapidly modulate cardiac activity allows for flexibility in responding to environmental demands with physiological and emotional arousal. Owing to the difference in their latencies of action, the oscillations in heart rate produced by the two autonomic branches occur at different speeds or frequencies.
The autonomic influences on heart rate are regulated remotely by the distributed network of brain areas composing the Central Autonomic Network (CAN). The CAN is critically involved in integrating physiological responses in the services of emotional expression, responding to environmental demands, goal-directed behavior, and homeostatic regulation. The neuroanatomical composition of the CAN includes cortical (medial prefrontal and insular cortices), limbic (anterior cingulate cortex, hypothalamus, central nucleus of the amygdala, bed nucleus of the stria terminalis), and brainstem (periaquaductal gray matter, ventrolateral medulla, parabrachial nucleus, the nucleus of the solitary tract) regions.
The CAN receives input from visceral afferents regarding the physiological conditions inside the body and input from sensory processing areas in the brain regarding the external sensory environment. The output of the CAN is transmitted to the sinoatrial node (and many other organs) through the SNS and PNS and directly influences heart rate.
Breathing air into the lungs temporarily gates off the influence of the parasympathetic influence on heart rate, producing a heart rate increase. Breathing air out of the lungs reinstates parasympathetic influence on heart rate, resulting in a heart rate decrease. This rhythmic oscillation in heart rate produced by respiration is called respiratory sinus arrhythmia. As only cardiac parasympathetic activity possesses a latency of action rapid enough to covariate with respiration, respiratory sinus arrhythmia is a phenomenon known to be entirely mediated by the PNS.
HRV is a measure of the continuous interplay between sympathetic and parasympathetic influences on heart rate that yields information about autonomic flexibility and thereby represents the capacity for regulated responding.
During HRV biofeedback, the amplitude of heart rate oscillations grows to many times the amplitude at rest, while the pattern becomes simple and sinusoidal. This pattern occurs in almost everyone and is often achievable within a fraction of a minute even in persons who have never previously been exposed to the technique. The mechanism for this effect lies in a confluence of processes:
(1) phase relationships between heart rate oscillations and breathing at specific frequencies,
(2) phase relationships between heart rate and blood pressure oscillations at specific frequencies,
(3) the activity of the baroreflex, and
(4) resonance characteristics of the cardiovascular system
HRV Biofeedback training can focus on increasing the amount of total HRV in a specific frequency range. To date, it appears optimal to increase the amount of heart rate change in the Low-Frequency Range (LF). For most persons that resonant frequency involves dominance of heart rate change in the Low-Frequency range, around 0.1 Hz. This 0.1 Hz frequency is most frequently produced by persons in a relaxed mental state, with a positive emotional tone, breathing diaphragmatically at a rate of about 5-7 breaths per minute. Relaxed breathing at six breaths per minute produces a spike of heart rate variability at 0.1 Hz. The amplitude of variation is higher because the effects of the baroreceptors on heart rate are added to the effects of slow breathing on heart rate. It has long been known that amplitude of HRV is systematically related to breathing frequency, with higher amplitudes achievable with slower respiration.
HRV biofeedback has been shown to be a powerful intervention for asthma. According to research data, the HRV BFB participants reported fewer symptoms, had better lung function, with no medication boosts.
In recent years a great deal of progress has been made in understanding the enteric nervous system and its autonomic regulation. Research has shown that esophageal pain thresholds are dramatically affected by six-per-minute breathing maneuvers. Improvement was mediated by the restoration of vagal tone presumably influenced by the HRV BFB. A recent study from the U.K. compared hypnosis to HRV BFB for irritable bowel syndrome. Both groups showed nice improvements with the HRV BFB group reporting slightly more reduction in symptoms.
There is promising literature using HRV biofeedback for various cardiologic disorders. Within cardiology, it is increasingly recognized that balancing SNS and PNS activity is a crucial component of cardiac health. There are exiting data that the HRV biofeedback has an impact on the heart muscle itself. The use of biofeedback in treating essential hypertension is well known within the field.
A recent study carried out in Germany has shown that adding HRV biofeedback to traditional back exercises and trigger point release produced the greatest pain relief in back pain patients. The mechanism hypothesized to be in play for ‘‘trigger points’’ (TPs) is known as ‘‘accentuated antagonism’’. It has been shown that good autonomic balance allows the PNS to govern the SNS in nonemergency situations. Therefore, the use of HRV biofeedback may be effective by blocking some of the sympathetic overflows to TPs.
There are few studies that show promise for conditions such as pregnancy-induced hypertension and preterm labor: the HRV BFB group had almost two weeks added gestation period with significantly heavier babies.
There have been a number of studies showing decreased depression levels with HRV biofeedback, including cases where the depression was secondary to trauma or anxiety.
The relevant literature shows that heart rate variability is associated with emotions and thoughts; the literature also shows that self-regulation training that incorporates HRV biofeedback can improve and behavior and, in turn, improves cognitive regulation of emotions.
HRV BIOFEEDBACK HOME-USE DEVICE
Heart rate variability biofeedback has enjoyed a good deal of popularity in recent years. A number of commercial products have been introduced ranging in price from $80 to over $200.
The HRV biofeedback equipment should have a sensor to measure heart rate (variability) with an electrocardiogram (ECG) or Blood Volume Pulse (BVP) and respiration sensor by using a breathing belt.