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ORIGINAL RESEARCH
published: 25 August 2017
doi: 10.3389/fpubh.2017.00222
Frontiers in Public Health | www.frontiersin.org
Edited by:
J. P. Ginsberg,
Dorn VA Medical Center,
United States
Reviewed by:
Richard Gevirtz,
Alliant International University,
United States
Inna Khazan,
Harvard Medical School,
United States
*Correspondence:
Patrick R. Steffen
steffen@byu.edu
Specialty section:
This article was submitted to Family
Medicine and Primary Care,
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Frontiers in Public Health
Received: 16June2017
Accepted: 08August2017
Published: 25August2017
Citation:
SteffenPR, AustinT, DeBarrosA and
BrownT (2017) The Impact of
Resonance Frequency Breathing on
Measures of Heart Rate Variability,
Blood Pressure, and Mood.
Front. Public Health 5:222.
doi: 10.3389/fpubh.2017.00222
The Impact of Resonance Frequency
Breathing on Measures of Heart
Rate Variability, Blood Pressure,
and Mood
Patrick R. Steffen*, Tara Austin, Andrea DeBarros and Tracy Brown
Brigham Young University, Provo, UT, United States
Heart rate variability biofeedback (HRVB) signicantly improves heart rate variability (HRV).
Breathing at resonance frequency (RF, approximately 6 breaths/min) constitutes a key
part of HRVB training and is hypothesized to be a pathway through which biofeedback
improves HRV. No studies to date, however, have experimentally examined whether
RF breathing impacts measures of HRV. The present study addressed this question by
comparing three groups: the RF group breathed at their determined RF for 15min; the
RF+1 group breathed at 1 breath/min higher than their determined RF for 15min; and
the third group sat quietly for 15min. After this 15-min period, all groups participated in
the Paced Auditory Serial Addition Task (PASAT) for 8min, and then sat quietly during a
10-min recovery period. HRV, blood pressure, and mood were measured throughout the
experiment. Groups were not signicantly different on any of the measures at baseline.
After the breathing exercise, the RF group reported higher positive mood than the other
two groups and a signicantly higher LF/HF HRV ratio relative to the control group, a
key goal in HRVB training (p<0.05). Additionally, the RF group showed lower systolic
blood pressure during the PASAT and during the recovery period relative to the control
group, with the RF+1 group not being signicantly different from either group (p<0.05).
Overall, RF breathing appears to play an important role in the positive effect HRVB has
on measures of HRV.
Keywords: resonance frequency breathing, heart rate variability, blood pressure, mood, biofeedback
Heart rate variability (HRV) is a key marker of health, mood, and adaptation, and hence improve-
ments in HRV improves health, mood, and adaptation to stress (1, 2). Heart rate variability biofeed-
back (HRVB) reliably increases HRV, mood, and adaptability (3, 4). A key aspect of HRVB involves
identifying each person’s unique resonance frequency (RF) breathing rate and then teaching them
how to breathe at this rate in the clinic and through home practice. No studies to date, however,
have examined if breathing at RF is an important aspect of HRVB training. e purpose of this
study was to examine whether dierent breathing rates would dierentially aect measures of HRV,
blood pressure, and mood. Specically, does RF breathing result in more positive outcomes relative
to other breathing rates?
Heart rate variability is the variation in time intervals between heart beats (5). Multiple physi-
ological systems inuence heart rhythm and greater uctuations in heart rhythm over time indi-
cate healthy systemic balance and ability to respond to physiological needs (3, 6). Consequently,
higher levels of HRV are indicative of a healthy heart and a marker of overall healthy physiological
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Steffen et al. Resonance Frequency Breathing
Frontiers in Public Health | www.frontiersin.org August 2017 | Volume 5 | Article 222
functioning (5). Low HRV, or less responsiveness to physiologi-
cal needs, predicts mortality and morbidity and also occurs in
depression, anxiety, and chronic stress (7). As an example, the
central nervous system uses negative feedback loops (such as
the baroreex) to maintain homeostatic balance in heart rate
and blood pressure while interacting with the environment (1).
However, these feedback loops become less sensitive with chronic
stress and sympathetic nervous system arousal found in physi-
cal and psychiatric disorders (3). High heart rates are inversely
correlated with the levels of HRV, as there is less opportunity
for variability between heart beats when they are closer (5). Low
HRV predicts negative outcomes in cardiovascular disease and in
all-cause mortality (8), with depression playing a signicant role
in cardiovascular disease as well (1).
Heart rate variability biofeedback reliably improves HRV.
Biofeedback is an interactive process where individuals directly
learn how to change their physiological activity (9). Sensors
placed on their skin measure physiological functions such as
heart rate, respiration, muscle tension, etc., and this informa-
tion is displayed on a computer screen in real time allowing
participants to become directly aware of and then change their
physiological functioning (5). HRVB is particularly benecial in
learning to regulate the physiological stress response. HRVB is a
relatively quick and inexpensive treatment, with protocols typi-
cally including ten 30-min sessions, although positive eects on
anxiety, depressive symptoms, and cognitive performance have
been found aer the rst session (10–12). HRVB interventions
are ecacious for both physical and mental disorders, including
treating depression, anxiety, panic disorder, as well as improv-
ing outcomes in patients with cardiac problems and asthma
(4,14,15).
A key aspect of HRVB is RF breathing. HRV is directly
inuenced by breathing and respiratory sinus arrhythmia (RSA).
RSA is the uctuation in heart rate corresponding to breathing,
with heart rate increasing with inhalation and decreasing with
exhalation (15). RSA typically occurs in the high frequency (HF)
range of HRV (0.15–0.4Hz) and is a measure of parasympathetic
activity (16). At resting breathing rates (between 9 and 24 breaths/
min), heart rate increases with inhalation at about the mid breath
point and heart rate decreases with exhalation at about the mid
breath point (5). RSA impacts gas exchange such that heart rate
tends to be higher when the air in the lungs is richest in oxygen
and exhalation occurs when carbon dioxide in the lungs is high-
est. Hayano etal. (17), however, found that the most ecient gas
exchange occurs when heart rate starts increasing at the beginning
of inhalation and decreasing as exhalation begins rather than at
the mid breath points. Synchrony of heart rate and breathing also
increases the amplitude of heart rate oscillations leading to high
levels of HRV.
Heart rate and breathing synchronize, or become resonance,
at about 6 breaths/min (0.1Hz). Each person has a unique RF
breathing rate, ranging typically between 4.5 and 7.0 breaths/min.
In studies of HRV biofeedback, the most common RF breathing
rate is 5.5 breaths/min (18). RF breathing rate is identied by
having the person breathe at 4.5, 5.0, 5.5, 6.0, 6.5 and 7.0 breaths/
min during EKG recording. HRV frequency and time domain
measures are then evaluated to nd which breathing rate results
in the largest changes in HRV. A common approach is to examine
the low frequency (LF) range (0.05–0.14) of the HRV spectrum
to nd the largest frequency spike, which usually occurs at about
0.1Hz. As people slow their breathing down and approach RF,
HRV amplitude increases signicantly. When a person breathes
at their identied RF breathing rate, heart rate and breathing
become synchronized and the highest levels of HRV are typically
obtained.
Although breathing at RF is a key part of HRVB training,
there are no published studies to date that have examined if RF
breathing is essential. We therefore tested the hypotheses that
breathing at RF would lead to improved HRV, blood pressure,
and mood using a randomized controlled design. Specically, we
examined three hypotheses. First, we hypothesized that the RF
group would show higher positive mood and decreased negative
mood and anxious arousal following breathing practice relative
to the RF+1 and control groups. Second, we hypothesized that
the RF group would score higher on the HRV measures of LF and
LF/HF ratio, and lower on HF relative to the RF+1 and control
groups. And third, we hypothesized that the RF group would
show decreased blood pressure reactivity during the PASAT
stressor relative to the RF+1 and control groups, and that LF/
HF ratio following breathing practice would predict decreased
blood pressure reactivity during the PASAT stressor and that this
eect would be strongest in the RF group.
METHOD
Participants
A convenience sample of 95 participants (60% female, average
age of 20) was recruited from undergraduate psychology classes
using an online recruitment site and randomized into three
experimental groups: RF breathing, breathing at 1breath/min
above established RF, and a control group that sat quietly. Class
credit was given for research participation. Participants were
excluded if they reported a history of heart disease or taking
medications that aect blood pressure or heart rate. is study
was approved by a university institutional review board and all
participants read and provided informed consent before starting
the study.
Measures
Heart Rate Variability
Heart rate variability was measured using both frequency domain
measures (LF, HF, and LF/HF ratio) and time domain measures
[standard deviation of normal to normal R-R intervals (SDNN)
and Root Mean Square of the Successive Dierences (RMSSD)].
HRV was measured using the Nexus 10 and Biotrace soware
(Mind media soware). Data were corrected for artifact and heart
variability measures were calculated using the Kubios program
(University of Finland). Power spectral analyses (LF and HF)
measures examine dierent frequencies: 0.15–0.4 Hz for HF,
and 0.04–0.15 for LF (3, 19). e SDNN measures the standard
deviation of the R spike to R spike. Larger SDNN values show
more variation in heart rate (3, 19). RMSSD is a time domain
measure of HRV, and measures the dierences between adjacent
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Frontiers in Public Health | www.frontiersin.org August 2017 | Volume 5 | Article 222
heart rates. RMSSD correlated with vagus-mediated components
of HRV (3, 19).
Blood Pressure
Data on heart rate, diastolic, and systolic blood pressure were
collected using a Dinamp Model 8100 automated blood pressure
monitor (Critikon Corporation, Tampa, FL, USA) that uses an
oscillometric method. Readings were taken placing a cu on the
upper non-dominant arm of the participant following manufac-
turer specications. Two blood pressure readings were averaged
for each time period.
Mood and Anxious Arousal
e Scale of Positive and Negative Emotions (SPANE) was used
to measure current mood. e SPANE consists of 12 items, 6
positive and 6 negative, to assess positive and negative emotions
over a specic time frame. ese are rated on a Likert scale from 1
(“very rarely or never”) to 5 (“very oen or always”). e SPANE
has demonstrated good internal consistency with Cronbach’s
alphas between 0.81 and 0.89. It also correlates from 0.57 to 0.70
with other mood scales (20). e anxious arousal subscale was
taken from the Mini Mood and Anxiety Questionnaire (21). e
anxious arousal subscale contains 10 items and is designed to
assess physiological symptoms associated with anxiety such as
feeling short of breath, cold hands, or trembling muscles. Items
are measured on a 5-point Likert scale, ranging from 0 (“Not at
all”) to 5 (“Extremely”) and the subscale has been shown to have
good internal consistency (α=0.85).
Procedure
Aer obtaining consent, participants were randomly assigned
to the RF, RF +1, or the control conditions. e experimental
conditions consisted of breathing at RF, breathing at one breath
above the RF (RF+1), and a control group who are sitting quietly.
Participants lled out an initial battery of measures, including
the anxious arousal subscale from the Mini Mood and Anxiety
Questionnaire, and SPANE. Researchers attached EKG sensors
to participants’ wrists and forearm. e participant also wore a
respiration belt and a blood pressure cu on their non-dominant
arm. RF was determined for all participants, used Rosenthal’s
HRV determination protocol. e pacer was set at ve dierent
frequencies (7, 5, 6.5, 5.5, and 6 breaths/min) for 2min, resting
1min between each pace. Because previous studies failed to nd
students breathing at 4.5 breaths/min, this rate was not included
in the present study. Participants then lled out self-report meas-
ures of typical stress responses. Participants in the biofeedback
conditions then continued to breathe for 15min, with those in t he
RF condition breathing at RF, and those in the RF +1 group at
one above their RF. Participants in the control condition sat qui-
etly with their eyes open for 15min. Aer this time, participants
lled out self-report measures of stress and anxiety symptoms. All
participants then took the Paced Auditory Serial Addition Task
[PASAT (22)] as a brief laboratory stressor, followed by measures
of mood and anxious arousal. Participants then sat quietly for
10min, followed by measures of mood and anxious arousal, and
were then thanked for their time.
Data Analysis
e purpose of this study was to examine the impact of dierent
breathing rates on physiological response using a randomized
controlled design. We therefore used repeated measures analysis
of variance to test the rst two hypotheses, analyzing the impact
of group membership on measures of heart variability, blood
pressure, and mood during breathing exercises (or sitting qui-
etly), during the PASAT stressor, and during a recovery period.
We also used hierarchical linear regression to test the last hypoth-
esis, examining if a measure of HRV (LF/HF) measured during
breathing practice predicted blood pressure response to the
PASAT stressor. All analyses were conducted using SPSS (IBM
SPSS version 23). ree hypotheses were examined.
RESULTS
Mood and Physiological Distress by
Experimental Group
e experimental groups did not dier on gender composition or
age, and there were no signicant dierences between groups on
reported positive mood, negative mood, or physiological distress
at baseline. e 3-Group×4-Time ANOVAs on positive mood,
negative mood, and physiological distress yielded signicant
main eects of time: F(3, 276)= 30.38, p< 0.001, η=0.25 for
positive mood; F(3, 276)=30.55, p<0.001, η=0.25 for negative
mood; and F(3, 276)=16.19, p<0.001, η=0.15 for physiological
distress, providing evidence that the experimental manipulations
impacted the participants. Compared to baseline, positive mood
fell signicantly during the PASAT stressor and then recovered
somewhat during the recovery period, whereas both negative
mood and physiological distress increased from baseline to the
PASAT stressor and then decreased during recovery.
e Group × Time interaction was signicant for positive
mood only, F(6, 276)=3.44, p<0.01, η=07. Follow-up contrasts
examining the changes from baseline to the end of the breathing
practice showed that individuals in the RF group had increased
positive mood whereas the other groups did not, F(2, 92)=10.73,
p< 0.001, η=0.19. ere were no signicant Group × Time
interactions for the PASAT and recovery periods.
Measures of HRV by Experimental Group
e main hypothesis of this study was that dierent rates of breath-
ing would dierentially impact measure of HRV, with RF breath-
ing leading to more benecial results. e 3-Group × 5-Time
ANOVAs on frequency domain measures of HRV (LF, HF, and
LF/HF) yielded signicant main eects of time: F(4, 372)=15.78,
p<0.001, η=0.15 for LF; F(4, 372)=4.13, p<0.01, η=0.04 for
HF; and F(4, 372)=12.07, p<0.001, η=0.12 for the LF/HF ratio.
e control showed little change over time in measures of HRV,
whereas the RF and RF+1 groups increased LF and decreased
HF during breathing practice and decreased LF and increased
HF during the PASAT stressor. Time domain measures of HRV
(SDNN and RMSSD) did not show main eect dierences over
time nor were there Group×Time interactions.
e Group× Time interactions were signicant for LF, HF,
and the LF/HF ratio, F(8, 372)=3.32, p<0.001, η=0.07 for LF,
FIGURE 2 | The RF and RF+1 groups showed decreased blood pressure
during breathing training compared to the control group. The RF group
showed the smallest increase (least reactivity) in blood pressure in response
to the stressor compared to the RF+1 and control groups.
FIGURE 1 | The RF group showed the largest LF/HF response to the
breathing practice, with the RF+1 showing minimal LF/HF changes and the
control group decreasing during this time period.
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Steffen et al. Resonance Frequency Breathing
Frontiers in Public Health | www.frontiersin.org August 2017 | Volume 5 | Article 222
F(8, 372)=2.18, p<0.05, η=0.05 for HF, and F(8, 372)=3.96,
p<0.001, η=0.08 for LF/HF. e RF group showed the largest
changes during the breathing exercise, particularly for the LF/
HF ratio which is a key variable tracked in HRVB. Follow-up
contrasts examining changes from baseline to the end of the
breathing practice revealed that the RF group increased in LF/
HF ratio following breathing practice, whereas the RF + 1
group remained about the same and the control decreased, F(2,
93)=4.64, p=0.01, η=0.09. Only the RF group was signicantly
higher than the control group, with the RF+1 not being dier-
ent from either group, indicating that a key therapeutic goal of
HRV-B was most clearly achieved in the RF group (Figure1).
Impact of Experimental Group on Blood
Pressure and Impact of LF/HF Ratio on
SBP and DBP
We also hypothesized that RF breathing would result in lower
blood pressure during breathing practice and reduced physiologi-
cal responsiveness during a lab stressor. e 3 Group×5-Time
ANOVAs for SBP, DBP, HR revealed signicant main eects with
physiology decreasing during breathing practice and increasing
the PASAT stressor, F(4, 292)= 36.71, p< 0.001, η= 0.34, for
SBP; F(4, 292) = 13.86, p< 0.001, η=0.16, for DBP; and F(4,
292)= 10.25, p< 0.001, η= 0.12, for HR, indicating that the
experimental manipulations impacted physiology as expected.
e Group×Time interactions were signicant for SBP and
DBP but not HR, F(8, 292)=3.53, p<0.001, η=0.09, for SBP, and
F(8, 292)=3.69, p<0.001, η=0.09, for DBP. During breathing
practice, both the RF and the RF+1 groups showed lower SBP
and DBP compared to the control group, F(2, 73)=3.56, p<0.05,
η=0.09 for SBP, and F(2, 73)=4.94, p<0.01, η=0.12 for DBP.
In response to the PASAT stressor, however, the RF group showed
lower SBP compared to both the RF+1 and control groups, F(2,
73)=3.29, p<0.05, η=0.04 for SBP, suggesting that RF breathing
buered the stress response to the PASAT (Figure2).
e nal hypothesis was that LF/HF ratio would predict blood
pressure response to the PASAT stressor. Using hierarchical linear
regression, it was found that higher LF/HF at the end of breath-
ing practice (controlling for baseline levels) predicted lower SBP
during the PASAT (β=−0.21, p<0.01) and during the recovery
period (β=−0.28, p<0.01). When examining eects by group, it
was found that the eect was strongest in the RF group, β=−0.43,
p<0.02 for recovery period. Similar results were found for DBP
with lower DBP found during recovery only (r=−0.26, p<0.05),
with the eect strongest for the RF group (r=−0.64, p<0.05).
ese analyses indicate that the higher the LF/HF ratio, the less
physiologically reactive people are to stress, with this eect being
driven primarily by the RF group.
DISCUSSION
We examined whether breathing at RF would improve HRV,
blood pressure, and mood, compared to breathing 1 breath/
min above RF and sitting quietly using a randomized controlled
design. Following the breathing exercise, the RF group reported
the highest positive mood and showed a higher LF/HF ratio.
Whereas the RF group increased signicantly in LF/HF ratio, the
RF+1 group did not change signicantly and the control group
decreased. e LF/HF ratio is a key variable in HRVB and only the
RF group displayed the increase that is sought for. e RF group
also showed larger reductions in BP, particularly in response to
the PASAT stressor. We also examined whether LF/HF ratio at the
end of breathing practice would predict less BP reactivity during
the subsequent PASAT stressor. Higher LF/HF did predict lower
BP reactivity and this eect was seen most strongly in the RF
group. Overall, results indicate that RF breathing contributes to
healthier physiological response and mood, supporting its use in
HRVB specically and stress reduction generally.
Resonance frequency breathing is a key part of HRVB pro-
tocols (3). A number of research studies, however, have found
positive results only emphasizing slow breathing or breathing at
6 breaths/min (23–25). Lin etal. (23) had healthy college students
breathe at 6.0 and 5.5 breaths/min and found that the 5.5 rate
resulted in higher HRV. RF breathing rate was not determined,
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Frontiers in Public Health | www.frontiersin.org August 2017 | Volume 5 | Article 222
rather everyone breathed at the same rate. Mason etal. (24) found
that breathing at 6 breaths/min as part of yoga exercise improved
oxygen saturation and baroreex sensitivity. Zautra et al. (25)
examined bromyalgia pain patients when they were breathing
normally and when breathing at half their normal rate and found
slower breathing was related to decreased pain and depressive
symptoms. A key nding of this study is that breathing at RF does
matter. It is not clear if this would be the case in all situations, but
there is evidence that HRVB and RF breathing results in stronger
eects (4). Future studies could continue this line of research
by examining slow breathing versus RF breathing with dierent
populations and diagnoses to examine these possibilities.
Vaschillo et al. (18, 26, 27) documented that in addition to
being an RF for breathing, there is also an RF for vascular tone,
and that these resonance frequencies interact. erefore, vascular
tone may be impacted by RF breathing in terms of BP response to
stress, with RF breathing decreasing BP and reducing BP response
during stress. at is what was found in this study. e RF group
increased their LF and HF/LF ratio following breathing practice,
and this predicted decreased BP during the PASAT stressor. is
conrms earlier research that those with higher HRV are more
physically and emotionally resilient (5), but goes one step further
to show that this can occur aer one 15-min session RF breathing
session.
Heart rate variability biofeedback potentially creates favora-
ble outcomes in physical and mental health disorders through
several mechanisms of action. Recent research has explored
how strengthening and activating the baroreex and vagal
nerve increase physical and emotional resilience (3). Increases
in LF and the HF/LF ratio indicate that these systems are being
activated and strengthened. Breathing at RF, versus breathing
near or slightly above RF, produced the highest LF/HF ratio,
which can be interpreted as higher levels of baroreex and vagal
nerve activity. As these are proposed mechanisms of action
for the reduction of symptoms in physical and psychological
disorders, breathing at RF will produce greater eects in HRV
interventions.
A limitation of this study is the cross-sectional design. While
positive changes were seen with only one session, it is unknown
what would happen over the course of weeks as HRVB is typi-
cally administered. Additionally, the sample consisted of college
students, so it is unknown if these results would be found in dif-
ferent age groups. We did not assess baroreex in this study which
would have been helpful in understanding the pathways through
which HRV changes occurred. A strength of this study was the
use of a randomized controlled design with participants not
being signicantly dierent on the variables assessed at baseline.
erefore, there is condence that the changes observed aer
exposure to the experimental conditions was not due to random
eects.
CONCLUSION AND FUTURE DIRECTIONS
Overall, evidence supports RF breathing as a key factor in HRVB.
RF breathing, compared to breathing at 1 breath above RF and
sitting quietly control group, leads to more positive outcomes,
resulted in a more positive mood, a higher LF/HF ratio (a key
variable in HRVB), and a decreased BP response to stress. is
study contributes to research on HRV showing that breathing
at RF, as opposed to breathing near RF, promotes more adaptive
physiological and emotional response. Future directions in this
line of research include examining these relationships longi-
tudinally over the course of HRVB, to study older age groups,
and to explore if these relationships hold in people with clinical
diagnoses such as depression or anxiety.
ETHICS STATEMENT
is study was carried out in accordance with the recommenda-
tions of Brigham Young University Institutional Review Board
with written informed consent from all subjects. All subjects gave
written informed consent in accordance with the Declaration of
Helsinki. e protocol was approved by the BYU Institutional
Review Board.
AUTHOR NOTES
Patrick R. Steen, Ph.D., Department of Psychology, Brigham
Young University.
AUTHOR CONTRIBUTIONS
PS was involved with study conceptualization, design, statistical
analysis, and writing up the manuscript. TA was involved with
study design, analysis, data collection, and writing. AD and TB
were involved with design, analysis, and data collection.
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