“If you want something you have never had, you must be willing to do something you have never done.”
― Thomas Jefferson
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If you think a heartbeat is a simple, regular rhythm that only varies with exertion, you misunderstand. While we feel our heartbeat’s dominant rhythm, it has many harmonics. These act as responsive metronomes that coordinate systems in the body.
The vagus nerve connects the brain to organs in the body. Most of the signals in the vagus travel from the body to the brain to inform and maintain homeostasis. While we identify our personalities as controlling our functions, the central nervous system tells another story: our body plays a major role in regulating our moods and personality.
While it keeps an even tempo, the rhythms of the heart are not simple or regular. The flow of blood through our bodies is both laminar and chaotic. These flow patterns are indicators of the health of many bodily systems, and the more aware we are of these rhythms the more we can coordinate their functions. Surprisingly, we can train better cardiac rhythms to improve both physiological and psychological health.
Rhythms
Heart rhythms range from fast atrial oscillations of a hundredth of a second to slow circadian rhythms varying over twenty four hours. These rhythms coordinate arousal, response, blood chemistry, gut activity, emotional balance, neurological coordination, hormone production, diurnal activity, the immune system, and probably everything else!
Rhythm is measured as the time between repeating structures, but also involves the shape of the pulse which reflects its harmonic components. Focusing on beats and the structures they contain measures rhythm in what’s called the time domain. This is what is easiest for us to sense and control because the time domain is sequential and specific, which is consonant with our awareness. Rhythm in the time domain is given by the pulse—which we can count—and correlates with our breath, level of arousal, and sense of time.
Harmonics measure rhythm in the frequency domain. This is measured as average patterns over time. Measuring these patterns requires the recording, comparison, and tabulation of their regularity.
We can hear auditory harmonics, and we can feel harmonics in our body as moods, comfort levels, and our ability to focus. Our temporal control affects our ability to rationalize, intellectualize, predict, and speak. We can slow ourselves down or speed ourselves up. We can be more or less reflective or reactive, and we can create more or less emotional environments.
We are more aware of ourselves and our heart rhythms in the time domain because we think in sequential terms. We are more aware of how we control ourselves in terms of cause and effect. While we are less aware of our cardiopulmonary and cognitive frequencies, we have some awareness of and control over them.
The shape of our pulse is a qualitative measure that combines rhythm and structure. A changing rhythm, which is what variability amounts to, requires changes in the dominant frequencies.
Higher frequencies contribute to the pulses’ small-scale structure. A completely smooth, oscillating pulse requires the organization of all frequencies. We can see this in smoothly oscillating waves of change in our heartbeat, blood oxygenation, blood pressure, and muscle tone.
We experience frequency control as a state of body and mind. Descriptions such as agitation, vigilance, relaxation, and flow-state describe dominant mind-body frequencies. We have varying degrees of psychological control over them. Psychologically impaired people typically have less control over these frequencies. The frequencies over which a person lacks control can be specific to their impairment (Montano et al. 2009; Forte 2019).
Something similar appears to be described by Traditional Chinese Medicine and its Theory of Pulses, which uses 28 poetic descriptions of the pulse taken manually (Al-Shura 2014). Our Western theory of the pulse is based on blood flow and the vascular system. The Eastern theory of pulses is based on life energy, or chi, and energetic centers in the body.
“Figure 1: Heart rate variability pattern for an individual participating in a deep breathing session: prior to initiating the deep breathing technique (left of the dotted line) and after starting with the technique (right of the dotted line). Note the change in emotional stress indicated by the shift from an erratic and disordered heart rhythm pattern (low coherence) to a sine wave-like (high coherence) pattern.” From Aritzeta et al. (2017)
HRV
The body-mind connection is the key to understanding the importance of the heart’s rhythms. It is clear that these rhythms guide our state and respond to changes in our environment. The degree to which these frequencies reflect and adapt is termed heart rate variability (HRV). The term is not precise because it includes all rhythms and responses, so we have to discriminate which of the body’s systems we’re talking about.
Microsecond heart rhythm changes are internal to the heart’s coordinated function. Changes over periods from 2.5 to 7 seconds correlate with respiration and are called the high-frequency band. Variability in this range is associated with emotional lability.
Changes over time spans of 7 to 25 seconds correlate with blood pressure and vascular elasticity. Decreased rhythmic variability in what’s called the low-frequency range correlates with age, morbidity, and impaired baroreflex function.
The very-low frequency band describes variations in the heart’s rhythm over periods from 25 to 300 seconds. These changes indicate a person’s ability to modulate arousal. A lack of very-low frequency variability is typical of people with chronic tension, such as post-traumatic stress (McCraty 2015).
A healthy personality responds to arousing and sedating situations, and a healthy heart responds similarly. And because of the extensive connections between the heart and mind, mental variability is reflected in the heart’s variability. These variabilities differ according to the time and frequency ranges over which they’re measured and encouraged.
Just as a healthy mind responds smoothly and appropriately, the heart should too. We can see the mind’s health in the heart’s rhythms, and we can improve the mind’s health by improving the heart’s rhythms. This can be done with psychotherapy, physiotherapy, and biofeedback.
“Heart rate variability reflects the capability of an organism to adapt and recover. Patients with reduced heart rate variability might need additional psychotherapeutic sessions to achieve the same symptom improvements as patients with retained heart rate variability. (The degree to which) psychotherapy might increase vagal activity can be indexed non-invasively by measuring heart rate and calculating interbeat variability, i.e., heart rate variability.
“High variability means greater opportunity for the organism to adapt to internal and external challenges. Consequently, reduced HRV is a predictor of disease risk, e.g., higher inflammatory state, morbidity, myocardial infarction, and mortality. HRV was found to be reduced in depression and anxiety disorders.” (Balint et al. 2023)
Cardio-Pulmonary Rhythm
Most of the heart’s energy is expended in pumping blood through the lungs, not the body. The heart and lung collaborate in perfusion of gasses into and out of the blood. The absorption of oxygen is enhanced by an increase in blood pressure, while improved release of carbon dioxide correlates with lower blood pressure. A healthy heart facilitates these exchanges by beating more rapidly on the inhale and more slowly on the exhale. This difference is only a few percent of the pulse rate and is not cognitively obvious, but it’s easily trained using a pulse sensor driving a graphical display of HRV.
“Respiratory Sinus Arrhythmia (RSA) is the variation in heart rate (HR) that accompanies breathing, such that the HR increases during inhalation and decreases during exhalation… It is mediated by the vagus nerve, a major parasympathetic nerve, such that it is stimulated in periods of calmness and relaxation and depressed during periods of stress. The amount of RSA can be quantified by the amplitude of peak-to-trough excursions in heart rate that occur with each breath.
“The amplitude of changes (in beats per minute) tends to be greater in healthy people than in sick people, in younger people than in older people, and in people who are aerobically more fit… those with major social deficits, particularly autism, have very low levels of RSA. Among married couples, those with good marriages tend to have high levels of RSA while interacting, while those with bad marriages tend to have less. Although little research has been done yet on effects of heart rate variability biofeedback on sociability, this is a potential application.” (Lehrer et al. 2020)
Since you have control of your breathing rate, it’s easy to train a person to coordinate breathing with their pulse when the pulse is displayed using a biofeedback device. People with responsive cardiopulmonary and neuropsychological systems are able to quickly improve their heart rate variability, often dramatically in my experience. People with poor cardiopulmonary or neuropsychological health have more difficulty, but improvement will be more important for their health.
“Cardiac coherence refers to a stable state of increased synchrony between the rhythms of different oscillatory systems, typically heart rate, respiration, and blood pressure. In practice, this coherent state is reflected by a more ordered and sine wave-like Heart Rate Variability waveform, oscillating at a frequency of approximating 0.1 Hz, the frequency at which the phase synchrony of heart rate and respiration occurs.” (Pham et al. 2021)
Biofeedback and Psychotherapy
Some studies claim the effectiveness of psychotherapy can be measured by its effect on HRV (Balint et al. 2023; Kiema et al. 2014). While interesting, it’s unclear how therapists can make use of this.
More efficacious is the combined application of heart rate variability biofeedback (HRVB) and psychotherapy to improve outcome measures in both physiological and psychological tone. Healthy people can quickly improve their HRV through inexpensive, noninvasive biofeedback. Those with ailments also improve, and while it would be reasonable to expect that greater effort would be required, the benefits would also be greater.
“Studies have found that HRVB does, in fact, produce improvement in a variety of physical and emotional conditions including anxiety, depression, hypertension, asthma, and pain, as well as improvement in various kinds of human performance including mental concentration and agility, athletics, dance, and music. The technique is easily learned and can be trained using inexpensive equipment, including several free smart phone applications. HRVB has been proposed as a psychotherapy component that specifically targets the neurovegetative components of emotional problems and may improve treatment effectiveness. Most people can achieve high-amplitude oscillations in HR after just a few minutes of training, and almost everyone can master the technique within one to four sessions of coaching.” (Lehrer et al. 2020)
Lehrer et al. (2020) compared the results of 58 controlled studies of HRVB training targeting various biological and psychological measures of health. Ten studies show HRVB yielded improvements at a 95% certainty, 41 showed HRVB yielded improvements at less than 95% certainty, and 3 showed no improvement. In 10 studies, the control group showed more improvement than the training group, but with less than 95% certainty. In no study did the control group outperform the training group with 95% or greater certainty.
“The psychological questionnaires at pre- and post-tests for the heart rate variability biofeedback (HRVB) and control groups. BDI-II, Beck Depression Inventory-II; cog., cognitive; som., somatic; BAI, Beck Anxiety Inventory; PSQI, Pittsburgh Sleep Quality Index; PSAS, Pre-Sleep Arousal Scale; phy., physical. (* indicates p<0.05).” Fig. 1 from Lin et al. 2019.
Referring to their study of 20 subjects with major depressive disorder (MDD) who did or did not receive psychotherapy combined with HRVB training, compared to controls who either did or did not receive HRVB, Caldwell and Steffen (2018) report, “It appears that combining heart rate variability biofeedback training with psychotherapy has the potential to significantly improve therapy outcomes.”
Training HRV
Biofeedback training involves presenting the user with a real-time display of their physiological states so that they can either adjust their state or recognize the actions that affect it. HRV training can be done using inexpensive, noninvasive equipment at home or in a clinician’s office. Clinic-based training has the benefit of more careful direction and data analysis.
Most HRV feedback data is collected using a finger monitor that records the intensity of light transmitted through the tissues. These devices, called photo plethysmographs or PPGs, appear in pulse oximeters, rings, watches, wrist, and body sensors. They are accurate during relaxation and mild stress, but are prone to large errors during any form of exercise. (Singstad et al. 2021). They are useful for biofeedback training when used judiciously.
Biofeedback’s salutary effect depends on multiple, simultaneous, real-time indicators presented in an integrated manner and with little or no intellectual instruction. Training requires the feedback, through sight or sound, of information that is otherwise difficult to sense or cannot be sensed at all. The feedback enables the trainee to gain an awareness of which of their actions have a controlling effect.
Reward and inhibition cues are added to the feedback to encourage the trainee to do more or less of whatever is changing the display. Typical rewards include more vibrant colors and clearer sounds, while typical inhibits include faded colors and muted sounds. These cues help teach trainees to control systems in ways that they are otherwise unaware. They can see how they’re performing, sense what they’re doing to cause the changes in feedback, and get a summary of their performance.
Supervised training ensures the training is regular and effective. Training can also be done at home. When done carefully with an effective tool, training can generate semi-permanent improvements in HRV after a half dozen, 10-minute sessions. With regard to the training of HRV, significant improvements have been reported after a single session of training (Prinsloo 2013). Improvement can be anything from enduring to evanescent depending partly on outside mechanical, medical, behavioral, or situation sources of dysregulation. Clearly, old habits can work against improvements learned through biofeedback.
Cellphone devices are ingenious in extracting HRV data by combing the phone’s flashlight, video camera, and software analysis ability. They provide a good introduction, but their accuracy and efficacy are questionable. Here are four other HRV biofeedback devices that generate HRV scores based on the shape of the pulse, and not just the time between heartbeats. This is a more effective measure of heart rate variability.
HeartMath Emwave2
The Emwave2 is a self-contained, handheld device that records data using either an ear clip PPG or a built-in finder sensor, and links to a computer program that can display real-time HRV or historical training results. The size of a pack of cigarettes, it can used as a handheld unit that provides a basic read-out separate from the computer graphs it can also generate. Its session-generated data is delayed by a few seconds as it displays a HRV score during each breath cycle.
Journey to the Wild Divine, Wild Divine, and Healing Rhythms
IOM skin conductance and photo plethysmograph sensors used in the Alive and Wild Divine biofeedback games.
Variously titled, this game was originally released for desk and laptop Windows-based computers in 2001. While the product is sometimes hard to find, it is inexpensive and has more features than most of the higher priced biofeedback products.
The original Wild Divine combined finger sensors used in various challenges in a fantasy environment. The sensors combined the measurement of Galvanic Skin Response (GSR) with photo plethysmography allowing for feedback based on the combination of emotional arousal and heart rhythm.
Current versions (as of 2023) use a PPG-only sensor incompatible with the original hardware component. The product is now supported by Wild Divine Inc. (https://wilddivine.com/) and runs on Windows, Mac, iOS, and Android operating systems.
Older versions can still be found for sale as used products. The older software will not run on Windows 10 or more recent operating systems in normal mode, but they can be launched in “compatibility mode.” This is an option in recent Windows systems that allows the use of software written for older versions of the operating system.
The game element complicates the software beyond a simple training tool, and the variety of graphical challenges train the low frequency components of HRV. In my experience, this combination allows one to improve HRV more quickly than the devices that use only a PPG, or the versions of Wild Divine that rely only on the PPG sensor.
Alive
Closely related to the Wild Divine products, the Alive Personal Biofeedback Software (https://www.somaticvision.com/) originally used the same GSR+PPG combined sensor hardware. Its latest version supports a wide variety of sensors and up to four sensors combined, through the addition of skin temperature and breath monitoring.
Alive provides more choices of audio-visual feedback that are both game-like and involve the control of abstract visual and auditory patterns. It also provides clinical support to train and track multiple training clients using an internet connection.
The advent of ubiquitous mobile technology and virtual reality environments is leading to new feedback displays capable of training more biological metrics. The extent to which biological control can be trained or learned is an open question (Kerr 2023, Stoller 2020). The new forms of biofeedback being developed will open new research questions and create new personal training products.
HeartMath Inner Balance™ Coherence Plus
This 3-module device combines an earlobe PPG sensor wired to a wearable recording device connected by Bluetooth to a cell phone app. Some real-time feedback is provided through the cellphone-based application. Beats per minute is graphically displayed in real time, but the HRV score is delayed until the end of each breath cycle.
The feedback emphasizes the combination of regular breathing and smooth variability in the heartbeat. The cellphone application provides visual feedback for pacing one’s breath. Effective HRV training depends on finding one’s optimal breathing rate, as this is the rate at which the heart resonates. Optimal pace differs between individuals and the user can adjust this breathing rate, but the setting of the rate is not automatic and relies on the user’s adjustment.
Both the Coherence Plus and Emwave2 display delayed HRV feedback scores. They update the score after each cycle, summarizing the previous 8 to 10-second breath period. Delayed feedback for actions that respond immediately, even a delay of a second, makes training more difficult (Whited 2014). Learning to ride a bicycle, for example, requires sensing the consequence of your actions within hundredths of a second.
Other Devices
Many wearable training devices that claim to train HRV are actually recording devices, not training devices. This includes smartwatches, headbands, armbands, and rings that provide downloadable, recorded data. These are monitoring, not training tools. Monitoring can help in discerning the effects of your daily habits, but they do not train your autonomic nervous system.
New devices, algorithms, applications, and combinations are being developed. More can be done in the analysis, combination, and presentation of data. Prices of consumer wearables will continue to drop.
Summary
Studies of Heart Rate Variability quickly descend into physiological measures and computational complexity. From a training perspective, this all ignores the simple and startling fact that it is one’s mood that affects one’s HRV more than any other action or intention.
HRV training is essentially mood training. It is plausible but unproven that training to improve one’s HRV can permanently improve one’s mood. “Heart rate oscillations can enhance emotion by entraining brain rhythms in ways that enhance regulatory brain networks (Mather and Thayer 2018).”
“HRV was positively associated with positive hedonic tone (cheerfulness) and positive tense arousal (calmness), and these effects were completely mediated by the habitual use of executive emotion regulation strategies.” — Geisler et al. (2010)
New devices, algorithms, applications, and combinations are being developed. The optimal device is the one that provides the most accurate, real-time feedback with the least distraction and the most convenience. More can be done in the analysis, combination, and presentation of data. Prices of consumer wearables will continue to drop.
Learning to regulate one’s autonomic nervous system through biofeedback is playing an increasingly important role in psychotherapy. Therapists should inform their clients of the potential benefits of biofeedback training. Psychotherapists who remain uninformed of the value of autonomic nervous system training are under-serving their clients.
References
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Balint, E. M., et al. (2023). Heart rate variability predicts outcome of short-term psychotherapy at the workplace. Psychophysiology, 60:e14150, https://doi.org/10.1111/psyp.14150
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