Do Longer Exhalations Increase HRV During Slow-Paced Breathing?

Slow-paced breathing at an individual's resonance frequency (RF) is a common element of heart rate variability (HRV) biofeedback training (Laborde et al. in Psychophysiology 59:e13952, 2022). Although there is strong empirical support for teaching clients to slow their respiration rate (RR) to the adult RF range between 4.5 and 6.5 bpm (Lehrer & Gevirtz, 2014), there have been no definitive findings regarding the best inhalation-to-exhalation (IE) ratio to increase HRV when breathing within this range. Three methodological challenges have frustrated previous studies: ensuring participants breathed at the target RR, IE ratio, and the same RR during each IE ratio. The reviewed studies disagreed regarding the effect of IE ratios. Three studies found no IE ratio effect (Cappo & Holmes in J Psychosom Res 28:265-273, 1984; Edmonds et al. in Biofeedback 37:141-146, 2009; Klintworth et al. in Physiol Meas 33:1717-1731, 2012). One reported an advantage for equal inhalations and exhalations (Lin et al. in Int J Psychophysiol 91:206?211, 2014). Four studies observed an advantage for longer exhalations than inhalations (Bae et al. in Psychophysiology 58:e13905, 2021; Laborde et al. in Sustainability 13:7775, 2021; Strauss-Blasche et al. in Clin Exp Pharmacol Physiol 27:601?60, 2000; Van Diest et al. in Appl Psychophysiol Biofeedback 39:171?180, 2014). One study reported an advantage for longer inhalations than exhalations (Paprika et al. in Acta Physiol Hung 101:273?281, 2014). We conducted original (N = 26) and replication (N = 16) studies to determine whether a 1:2 IE ratio produces different HRV time-domain, frequency-domain, or nonlinear metrics than a 1:1 ratio when breathing at 6 bpm. Our original study found that IE ratio did not affect HRV time- and frequency-domain metrics. The replication study confirmed these results and found no effect on HRV nonlinear measurements.

Adding Core Muscle Contraction to Wrist-Ankle Rhythmical Skeletal Muscle Tension Increases Respiratory Sinus Arrhythmia and Low-Frequency Power.

Paced breathing and rhythmical skeletal muscle tension (RSMT) at an individual's resonance frequency [~ 6 breaths or contractions per min (cpm)] can stimulate the arterial and vascular tone baroreflexes. Lehrer (Appl Psychophysiol Biofeedback 1-10, 2022, https://doi.org/10.1007/s10484-022-09535-5 ) has explained that the stimulation rate is important, not the modality. Early RSMT protocols differed in the muscles recruited and whether legs were crossed or uncrossed (in France et al. Clin Physiol Funct Imaging 26: 21-25, 2006, https://doi.org/10.1111/j.1475-097X.2005.00642.x ; Leher et al. Biol Psychol 81: 24-30, 2009, https://doi.org/10.1016/j.biopsycho.2009.01.003 ; Vaschillo et al. Psychophysiology, 48: 927-936, 2011, https://doi.org/10.1111/j.1469-8986.2010.01156.x ). Whereas core muscle RSMT with crossed legs and wrist-ankle RSMT with uncrossed legs produced resonance effects, researchers have not directly compared the effect of these exercises on respiratory sinus arrhythmia (RSA) and low-frequency (LF) power. The current within-subjects experiment investigated whether crossing the legs and recruiting core muscles enhances wrist-ankle RSMT effects on RSA and LF power. We trained 35 participants to complete 6-cpm wrist-ankle RSMT (ankles uncrossed), 6-cpm wrist-core-ankle RSMT (ankles crossed), and a control condition in which participants sat quietly (ankles uncrossed) without performing RSMT. We predicted that 6-cpm wrist-core-ankle RSMT would produce greater heart rate (HR), HR Max-HR Min, and LF power than the other conditions. The experimental findings supported our predictions. Both RSMT conditions produced greater HR, HR Max-HR Min, and LF power than the control condition. Wrist-core-ankle yielded greater HR and HR Max-HR Min than wrist-ankle RSMT. Future research should compare wrist-ankle and wrist-core-ankle RSMT with legs crossed. The practical implication for HRV biofeedback training is that wrist-core-ankle RSMT with legs crossed may more powerfully stimulate the baroreflex than wrist-ankle RSMT with legs uncrossed.

Susceptibility to peer influence in adolescents: Associations between psychophysiology and behavior.

The current study investigated in-the-moment links between adolescents' autonomic nervous system activity and susceptibility to three types of peer influence (indirect, direct, continuing) on two types of behavior (antisocial, prosocial). The sample included 144 racially ethnically diverse adolescents (46% male, 53% female, 1% other; M age  = 16.02 years). We assessed susceptibility to peer influence behaviorally using the Public Goods Game (PGG) while measuring adolescents' mean heart rate (MHR) and pre-ejection period (PEP). Three key findings emerged from bivariate dual latent change score modeling: (1) adolescents whose MHR increased more as they transitioned from playing the PGG alone (pre-influence) to playing while simply observed by peers (indirect influence) displayed more prosocial behavior; (2) adolescents whose PEP activity increased more (greater PEP activity = shorter PEP latency) as they transitioned from indirect influence to being encouraged by peers to engage in antisocial behavior (direct influence) engaged in more antisocial behavior; and (3) adolescents whose PEP activity decreased less as they transitioned from direct influence on prosocial behavior to playing the PGG alone again (continuing influence) displayed more continuing prosocial behavior (marginal effect). The discussion focuses on the role of psychophysiology in understanding adolescents' susceptibility to peer influence.

An Undergraduate Program with Heart: Thirty Years of Truman HRV Research.

This article celebrates the contributors who inspired Truman's heart rate variability (HRV) research program. These seminal influences include Robert Fried, Richard Gevirtz, Paul Lehrer, Erik Peper, and Evgeny Vaschillo. The Truman State University Applied Psychophysiology Laboratory's HRV research has spanned five arcs: interventions to teach diaphragmatic breathing, adjunctive procedures to increase HRV, HRV biofeedback (HRVB) training studies, the concurrent validity of ultra-short-term HRV measurements, and rhythmical skeletal muscle tension strategies to increase HRV. We have conducted randomized controlled trials, primarily using within-subjects and mixed designs. These studies have produced eight findings that could benefit HRVB training. Effortful diaphragmatic breathing can lower end-tidal CO2 through larger tidal volumes. A 1:2 inhalation-to-exhalation (I/E) ratio does not increase HRV compared to a 1:1 I/E ratio. Chanting "om," listening to the Norman Cousins relaxation exercise, and singing a fundamental note are promising exercises to increase HRV. Heartfelt emotion activation does not increase HRV, enhance the effects of resonance frequency breathing, "immunize" HRV against a math stressor, or speed HRV recovery following a math stressor. Resonance frequency assessment achieved moderate (r = 0.73) 2-week test-reliability. Four weeks of HRVB training increased HRV and temperature, and decreased skin conductance level compared with temperature biofeedback training. Concurrent-validity assessment of ultra-short-term HRV measurements should utilize rigorous Pearson r and limits of agreement criteria. Finally, rhythmical skeletal muscle tension can increase HRV at rates of 1-, 3-, and 6-cpm. We describe representative studies, their findings, significance, and limitations in each arc. Finally, we summarize some of the most interesting unanswered questions to enable future investigators to build on our work.

Rhythmic Skeletal Muscle Tension Increases Heart Rate Variability at 1 and 6 Contractions Per Minute.

Breathing at the resonance frequency (~ 6 breaths per min) produces resonance effects on baroreflex gain, blood pressure, vascular tone, and therapeutic benefits. Evgeny Vaschillo and Paul Lehrer have emphasized that the stimulation frequency is critical for producing resonance effects in the cardiorespiratory system. Although clinicians overwhelmingly use paced breathing to increase HRV, other promising methods exist. Vaschillo, Lehrer, and colleagues have shown that presenting non-respiratory stimulation at 0.1 Hz-pictures with an emotional valence or rhythmical muscle tensing-amplifies oscillations in heart rate, blood pressure, and vascular tone. Participants in the present study included 49 undergraduate students randomly assigned to one of six different orders of 5-min trials of 1, 6, and 12 muscle contractions per min (cpm), separated by 3-min buffer periods intended to minimize carryover. This randomized controlled trial replicated the Vaschillo et al. (Psychophysiology 48:927-936, 2011. https://doi.org/10.1111/j.1469-8986.2010.01156.x ) finding that 6-cpm RSMT can produce a PkFreq of ~ 0.10 Hz, similar to 6-bpm RF breathing. RSMT at 1 and 6 cpm increased five time-domain metrics (HR Max-HR Min, RMSSD, SDNN, TI, and TINN), one frequency-domain metric (LF power), and three non-linear metrics (D2, SD1, SD2) significantly more than RSMT at 12 cpm. There were no differences between 1 and 6 cpm on these measures. The 1-cpm rate (~ 0.02 Hz) may have stimulated the hypothesized vascular tone baroreflex between 0.02 and 0.055 Hz. RSMT at 1 or 6 cpm provides clients with an alternative exercise for increasing HRV for patients who find slow-paced breathing challenging or medically unsafe.

Pre-Pandemic Peer Relations Predict Adolescents' Internalizing Response to Covid-19.

The goal of the current longitudinal study was to investigate the role of adolescents' peer victimization and aggression prior to COVID-19 on the change in their depressive and anxious symptoms from pre- to mid-pandemic. We hypothesized that, although adolescents overall would display an increase in internalizing symptoms from pre- to mid-pandemic, this response would be weakened or perhaps even reversed when adolescents experienced high levels of victimization or aggression prior to the pandemic. Participants included 96 racially/ethnically diverse adolescents (42 males, 53 females; 1 other) with an average age of 16.79 years (SD = 0.60). At Time 1 (T1; June 2019 through February 2020; pre-pandemic), adolescents completed self-report measures of their peer relations (aggression, victimization) and internalizing symptoms (depressive, anxious). At Time 2 (T2; May through July 2020; mid-pandemic), adolescents completed self-report measures of their internalizing symptoms (depressive, anxious). On average, adolescents' anxious and depressive symptoms increased from T1 to T2, although they exhibited substantial variability, with reports ranging from decreasing symptoms to increasing symptoms. Although on average adolescents reported increases in anxious symptoms from T1 to T2, adolescents with higher T1 peer victimization reported less positive change in anxious symptoms. Similarly, although on average adolescents reported increases in depressive symptoms from T1 to T2, adolescents with higher levels of T1 aggression reported less positive change in depressive symptoms from T1 to T2. Discussion focused on restrictions on in-person peer interactions necessitated by COVID-19 that may reduce adolescents' distress when their pre-pandemic daily lives were characterized by negative peer relations.

Using Three Reporters to Identify Pre-Adolescent Peer Victims through Latent Profile Analysis.

The goals of the current study were to use a three-reporter methodology and multi-level Latent Profile Analysis: (a) to determine the victim groups that emerge; (b) to evaluate the stability of victim groups over one school year; and (c) to examine differences among victim groups across the adjustment constructs of aggression, depression, anxiety, and negative peer relations. Our sample included 1440 racially/ethnically diverse 4th- and 5th-grade children (Mage = 10.15; 50% female). At the beginning (T1) and end (T2) of the school year, children completed both self and peer reports of victimization, teachers reported on students' victimization, and we collected data from multiple reporters on aggression, depression, anxiety, and negative peer relations. At T1, two groups emerged: non-victims (low across all reporters) and victims (high across all reporters). At T2, four groups emerged: non-victims (low across all reporters), moderate victims (moderate across all reporters), discordant high victims (high on self report, very high on peer report, moderate on teacher report), and concordant high victims (high across all reporters). The stability of victim groups from T1 to T2 was largely driven by non-victims; T1 victims dispersed fairly evenly across the four groups at T2. In term of adjustment, non-victims fared best across time points and adjustment constructs. At T2, the three victim groups increased in maladjustment from moderate victims to discordant high victims to concordant high victims. These findings support the use of three-reporter assessment and a multi-level LPA approach to identify children victimized by their peers.

A Critical Review of Ultra-Short-Term Heart Rate Variability Norms Research.

Heart rate variability (HRV) is the fluctuation in time between successive heartbeats and is defined by interbeat intervals. Researchers have shown that short-term (∼5-min) and long-term (≥24-h) HRV measurements are associated with adaptability, health, mobilization, and use of limited regulatory resources, and performance. Long-term HRV recordings predict health outcomes heart attack, stroke, and all-cause mortality. Despite the prognostic value of long-term HRV assessment, it has not been broadly integrated into mainstream medical care or personal health monitoring. Although short-term HRV measurement does not require ambulatory monitoring and the cost of long-term assessment, it is underutilized in medical care. Among the diverse reasons for the slow adoption of short-term HRV measurement is its prohibitive time cost (∼5 min). Researchers have addressed this issue by investigating the criterion validity of ultra-short-term (UST) HRV measurements of less than 5-min duration compared with short-term recordings. The criterion validity of a method indicates that a novel measurement procedure produces comparable results to a currently validated measurement tool. We evaluated 28 studies that reported UST HRV features with a minimum of 20 participants; of these 17 did not investigate criterion validity and 8 primarily used correlational and/or group difference criteria. The correlational and group difference criteria were insufficient because they did not control for measurement bias. Only three studies used a limits of agreement (LOA) criterion that specified a priori an acceptable difference between novel and validated values in absolute units. Whereas the selection of rigorous criterion validity methods is essential, researchers also need to address such issues as acceptable measurement bias and control of artifacts. UST measurements are proxies of proxies. They seek to replace short-term values which, in turn, attempt to estimate long-term metrics. Further adoption of UST HRV measurements requires compelling evidence that these metrics can forecast real-world health or performance outcomes. Furthermore, a single false heartbeat can dramatically alter HRV metrics. UST measurement solutions must automatically edit artifactual interbeat interval values otherwise HRV measurements will be invalid. These are the formidable challenges that must be addressed before HRV monitoring can be accepted for widespread use in medicine and personal health care.

A Practical Guide to Resonance Frequency Assessment for Heart Rate Variability Biofeedback.

Heart rate variability (HRV) represents fluctuations in the time intervals between successive heartbeats, which are termed interbeat intervals. HRV is an emergent property of complex cardiac-brain interactions and non-linear autonomic nervous system (ANS) processes. A healthy heart is not a metronome because it exhibits complex non-linear oscillations characterized by mathematical chaos. HRV biofeedback displays both heart rate and frequently, respiration, to individuals who can then adjust their physiology to improve affective, cognitive, and cardiovascular functioning. The central premise of the HRV biofeedback resonance frequency model is that the adult cardiorespiratory system has a fixed resonance frequency. Stimulation at rates near the resonance frequency produces large-amplitude blood pressure oscillations that can increase baroreflex sensitivity over time. The authors explain the rationale for the resonance frequency model and provide detailed instructions on how to monitor and assess the resonance frequency. They caution that patterns of physiological change must be compared across several breathing rates to evaluate candidate resonance frequencies. They describe how to fine-tune the resonance frequency following an initial assessment. Furthermore, the authors critically assess the minimum epochs required to measure key HRV indices, resonance frequency test-retest reliability, and whether rhythmic skeletal muscle tension can replace slow paced breathing in resonance frequency assessment.

Corrigendum: A Practical Guide to Resonance Frequency Assessment for Heart Rate Variability Biofeedback.

[This corrects the article DOI: 10.3389/fnins.2020.570400.].