HRV AS A RESEARCH TOOL IN YOGA

Abstract

A wide range of studies have reported HRV analyses of immediate, short and long term effects of Yoga and its different techniques. A Pubmed, Medline and Google Scholar search with regard to HRV and the terms Yoga / Pranayama / relaxation / meditation revealed 33 eligible studies published in indexed, peer reviewed journals. Of these, 21 were on acute / immediate effects of different techniques (Asana, Pranayama and Meditation) while 11 reported the effects of training programmes ranging from 2 days to 4 months. The subject population of most studies was primarily normal, healthy volunteers of either/ both gender in 29 of them while 4 dealt with HRV studies in pregnant women, smokers on a cessation programme, patients of unipolar depression and post traumatic stress syndrome. While the majority gives evidence of enhanced parasympathetic activity and decreased sympathetic activity with improved SVB; a few strike a discordant note. Individual techniques are seen to have different effects as evidenced in acute studies on forced uninostril breathing and Kapalabhati / high frequency Yogic breathing. The tools of HRV analysis are highly sensitive to various factors such as the frequency of breathing, vocalization, mental activities and physical posture and hence have limitations with regard to Yoga studies. Innovative thoughts and novel methods need to be developed and applied if we are to understand the intrinsic effects of this ancient art and science that is as relevant today as it was millennia ago. (This review paper was prepared for the Souvenir of the CME–cum- Workshop on “Heart rate variability: a diagnostic and research tool.” Organised by the Department of Physiology, MGMCRI, Puducherry on 12.06.2012.) Published as a full paper in Yoga Mimamsa 2012; 44 (3): 188-199.

Full text

i
iÉnäùEòÉä%´Éʶɹ]õ: ʶɴÉ: Eäò´É±ÉÉä%½þ¨É *
I alone persist : Blissful : Absolute.
ºÉ´ÉÈ JÉα´ÉnÆù ¥ÉÀ *
All this is, indeed, Brahman
xÉä½þ xÉÉxÉÉκiÉ ÊEò\SÉxÉ *
There is nothing here apart from it
¶É®úÒ®ú¨ÉÉtÆ JɱÉÖ vɨÉǺÉÉvÉxɨÉ *
Surely Health is the primary requisite of spiritual life.
October 2012
Vol. XLIV No. 3
KAIVALYADHAMA
SWAMI KUVALAYANANDA MARG,
LONAVLA - 410 403 (Maharashtra), INDIA
• E-mail: kdham@vsnl.com • Tel. : 091-2114-273001
• Fax : 091-2114-271983 • Website: www.kdham.com
ºÉÉä%½þ¨É *
YOGA-MÌMËêSË
(Recommended by the Govt. of India, Ministry
of Education for the Libraries of Universities
and Physical Education Training Institutions
Vide Letter No : F.9-4/68,YS-4 dated 15.7.1968,
Regd.No. R.N.11402-58, ISSN:0044-0507)

Yoga M¢m¡Æs¡, Vol. XLIV No. 3 : 188-199, Oct, 2012
HRV AS A RESEARCH TOOL IN YOGA
Bhavanani, Ananda Balayogi*
Abstract
A wide range of studies have reported HRV analyses of immediate, short and long term
effects of Yoga and its different techniques. A Pubmed, Medline and Google Scholar search with
regard to HRV and the terms Yoga / Pr¡¸¡y¡ma / relaxation / meditation revealed 33 eligible
studies published in indexed, peer reviewed journals. Of these, 21 were on acute / immediate
effects of different techniques (Ësana, Pr¡¸¡y¡ma and Meditation) while 11 reported the effects
of training programmes ranging from 2 days to 4 months. The subject population of most studies
was primarily normal, healthy volunteers of either/ both gender in 29 of them while 4 dealt with
HRV studies in pregnant women, smokers on a cessation programme, patients of unipolar
depression and post traumatic stress syndrome. While the majority gives evidence of enhanced
parasympathetic activity and decreased sympathetic activity with improved SVB; a few strike a
discordant note. Individual techniques are seen to have different effects as evidenced in acute
studies on forced uninostril breathing and Kap¡labh¡ti / high frequency Yogic breathing. The
tools of HRV analysis are highly sensitive to various factors such as the frequency of breathing,
vocalization, mental activities and physical posture and hence have limitations with regard to
Yoga studies. Innovative thoughts and novel methods need to be developed and applied if we are
to understand the intrinsic effects of this ancient art and science that is as relevant today as it was
millennia ago.
Key Words : HRV, Yoga, Pr¡¸¡y¡ma, Relaxation, Kap¡labh¡ti, Google.
INTRODUCTION
In the past few decades, many researchers have investigated the effects of Yoga on markers of
sympathetic / parasympathetic activation and cardiovagal function. A review by Innes et al
identified 42 such studies with over 85% of them offering some evidence that Yoga promotes a
reduction in sympathetic activation, enhancement of cardiovagal function, and a shift in autonomic
nervous system (ANS) balance from primarily sympathetic to parasympathetic. (1) The key changes
they reviewed included significant reductions in respiratory and heart rate, in cortisol
concentrations, catecholamine levels, and renin activity, in skin conductance, and in cardiovascular
response to stress, as well as significant increases in heart rate variability (HRV) and baroreflex
sensitivity.
* Programme Co-ordinator ACYTER, JIPMER, Pondicherry, India. Email: yognat@gmail.com
Website: www.jipmer.edu/ACYTER/main.html
YM, Vol. XLIV No. 3 188 Bhavanani (2012)

HRV, the beat-to-beat alterations in heart rate, is a simple noninvasive measurement for
investigating autonomic influence on the cardiovascular system and may be evaluated by time
domain and frequency domain methods. Time domain analysis is a simple method to quantify
overall HRV whereas power spectral analysis provides a means of studying different mechanisms
responsible for variability in instantaneous heart rates.(2) A reduced HRV can be used as a predictor
of hypertension, development of diabetic neuropathy, cerebrovascular disease, congestive heart
failure, and lethal arrhythmic complications after an acute myocardial infarction.(3) Low HRV
and baroreflex sensitivity reflect impaired cardiovagal adaptability and suggest excessive
sympathetic and/or insufficient parasympathetic tone that are, in turn, strong independent predictors
of cardiovascular morbidity and mortality. In contrast, high HRV and baroreflex sensitivity are
generally considered to indicate good cardiovagal adaptability and SVB, permitting greater
responsivity and sensitivity to changing environmental demands. (1)
Streeter et al., (2012) recently proposed a theory to explain the benefits of Yoga practices in
diverse, frequently comorbid medical conditions based on the concept that Yoga practices reduce
allostatic load in stress response systems such that optimal homeostasis is restored. (4).
They hypothesized that stress induces an:
1. Imbalance of the ANS with decreased parasympathetic and increased sympathetic activity,
2. Under activity of the gamma amino-butyric acid (GABA) system, the primary inhibitory
neurotransmitter system, and
3. Increased allostatic load.
They further hypothesized that Yoga-based practices
1. Correct underactivity of the parasympathetic nervous system and GABA systems in part
through stimulation of the vagus nerves, the main peripheral pathway of the parasympathetic
nervous system, and
2. Reduce allostatic load.
According to the theory proposed by Streeter et al, the decreased parasympathetic nervous
system and GABAergic activity that underlies stress-related disorders can be corrected by Yoga
practices resulting in amelioration of disease symptoms. HRV testing has a great role to play in
our understanding intrinsic mechanisms behind such potential effects of Yoga.
Innes et al., had earlier (2005) also postulated two interconnected pathways (given below) by
which Yoga reduces the risk of cardiovascular diseases through the mechanisms of parasympathetic
activation coupled with decreased reactivity of sympathoadrenal system and HPA axis.(1)
YM, Vol. XLIV No. 3 189 Bhavanani (2012)
HRV AS A RESEARCH TOOL IN YOGA

YM, Vol. XLIV No. 3 190 Bhavanani (2012)
HRV AS A RESEARCH TOOL IN YOGA
STUDIES USING HRV TO EVALUATE EFFECTS OF YOGA
A Pubmed, Medline and Google Scholar search with regard to HRV and the terms Yoga /
Pranayama / relaxation / meditation revealed 33 eligible studies published in indexed, peer reviewed
journals. (2, 5-36) Of these, 21 were on acute / immediate effects of different techniques (Ësana,
Pr¡¸¡y¡ma and Meditation) while 11 reported the effects of training programmes ranging from
2 days to 4 months. The subject population of most studies was primarily normal, healthy volunteers
of either/ both gender in 29 of them while 4 dealt with HRV studies in pregnant women (32),
smokers on a cessation programme (13), patients of unipolar depression (33) and post traumatic
stress syndrome (35). Although evidence for a beneficial influence on sympathovagal (SVB) balance
due to Yoga is quite consistent overall across the diverse array of studies, there are many limitations
that hinder conclusive interpretation of findings.
In 1991 Stancák et al., reported a decreased cardiac vagal modulation during high frequency
Yogic breathing in 17 advanced Yoga practitioners by a spectral analysis of the time series of
beat to beat series of the R-R intervals as well as systolic and diastolic blood pressure.(5) This
may very well be the earliest study in Yoga using concepts of HRV analysis. The next published
report on Yoga using HRV was in 1997 by Bowman et al., who reported on baroreflex sensitivity
in healthy elderly persons concluding that alpha HF (reflecting para-sympathetic activity)
increased following 6 weeks of Yoga training but not after aerobic exercise. (6)
Raghuraj et al., (1998) reported the comparative effects of Kap¡labh¡ti and N¡·¢ áuddi thus

YM, Vol. XLIV No. 3 191 Bhavanani (2012)
HRV AS A RESEARCH TOOL IN YOGA
becoming the first ones to use HRV analysis to differentiate effects of slow and fast Pr¡¸¡y¡mas
and their effects on the ANS.(7) They concluded that Kap¡labh¡ti modifies autonomic status by
increasing sympathetic activity with reduced vagal activity. Bernardi et al., (2001) studied breathing
patterns and cardiovascular autonomic modulation during hypoxia induced by simulated altitude
in 10 western Yoga trained subjects giving evidence that sympathetic activation following
simulated altitude was blunted in Yoga trainees.(8) Three more studies followed soon from
SVYASA University, Bangalore with Vempati and Telles reporting on Yogic relaxation (9, 10) and
Manjunath and Telles on Sirsasana(11). The first report on HRV from JIPMER was a report on
Shavasan training in students by Madanmohan et al., in 2004.(2) This was soon followed by another
study discussing the correlation between short-term HRV indices and heart rate, blood pressure
indices, pressor reactivity to isometric handgrip in healthy young male subjects(37). Recently
researchers at JIPMER presented papers on the immediate effects of uninostril breathing
techniques(38) as well as on the cardiac autonomic effects of Shavasan in patients of heart failure(39).
Other short term and long term studies on Yoga and its techniques in diabetic and hypertensive
patient populations are in progress.
Dhy¡na or meditation is an integral part of Patanjali's AÀ¶¡µga Yoga though in modern times
it has been highlighted individually with many newer techniques becoming popular worldwide.
There are at least 13 acute / immediate studies on different forms of meditation such as Cyclic
meditation, Zen meditation, Ku¸·alin¢ meditation, Chi meditation, loving-kindness meditation,
nondirective meditation and the contemplative chanting of the rosary or the Mantra 'Om Ma¸i
Padme Om'.(12-25) of these studies, 12 reported improvement of HRV power / SVB / increased
para-sympathetic / decreased sympathetic while one reported increase in stochastic nature and
decrease in nonlinear nature of the signal during Chi meditation with significant decrease in
degree of nonlinearity and stochastic nature occurs during Ku¸·alin¢ meditation.(12) One of the
interesting reports was that that individuals exhibiting acute increases in HF-HRV from resting
baseline to meditation smoked fewer cigarettes at follow-up than those who exhibited acute
decreases in HF-HRV.(13)
Chaya et al., reported that subjects who had practiced Yoga for a year had higher resting
sympathetic activity compared with controls as evidenced by significantly higher LF power,
lower HF power and higher LF/HF ratio.(26) This was attributed to the stress of a novel experimental
setting, since in contrast to the Yoga group many of the subjects in the control group had undergone
other experimental procedures such as protein kinetic studies in the experimental laboratory. In
contrast, Khattab et al., have reported that relaxation by yoga after 5 weeks of training is associated

YM, Vol. XLIV No. 3 192 Bhavanani (2012)
HRV AS A RESEARCH TOOL IN YOGA
with a significant increase of cardiac vagal modulation.(29) Another randomized control trial in
Brazil reported significant decreases in LF as well as LF/HF ratio following 4 months of respiratory
yoga training and concluded that it may be beneficial for the elderly healthy population by
improving respiratory function and SVB.(31)
A large scale study in the USA of 239 employee volunteers reported that the mind-body
interventions showed significantly greater improvements on perceived stress, sleep quality, and
the heart rhythm coherence ratio of HRV.(36) They concluded that both mindfulness-based and
therapeutic yoga programs may provide viable and effective interventions to target high stress
levels, sleep quality, and autonomic balance in employees.
DIFFICULTIES IN HRV ANALYSIS OF YOGA TECHNIQUES
It is difficult to analyse frequency domain studies of HRV during any yogic manoeuvre
especially Pr¡¸¡y¡ma, as respiratory frequency, tidal volume and minute ventilation influences
both low frequency and respiratory frequency RR interval power spectra. Respiration must be
controlled if RR interval power spectra are to be interpretable.(40) When performing HRV it is
essential that there is a simultaneous recording of respiration alongside ECG and BP measurements.
Since Pr¡¸¡y¡ma involves altering breathing frequency, ratio and depth - as such the HRV spectra
cannot be interpreted as they often are routinely and spectral analysis may not give useful
information beyond that contained in the time domain.
For short manoeuvres the mean RR interval and simple time domain measures of RR interval
variability: SDNN; and pNN50 if possible are useful. Spectral analysis of HRV may not yield
any further useful information because each manoeuvre may be associated with a distinct pattern
of breathing (depth, ratio and frequency). Being able to quantify both depth and frequency of
breathing will be ideal but the minimum that needs to be known for correct interpretation is
respiratory frequency as the association of respiratory frequency, tidal volume and minute
ventilation with short-term autonomic control is well established.(40) Simple mental and verbal
activities markedly affect HRV through changes in respiratory frequency. This possibility should
be taken into account when analyzing HRV without simultaneous acquisition and analysis of
respiration.(41) Autonomic rhythms measured during different breathing protocols have much in
common but it has been reported that a stepwise protocol without stringent control of inspired
volume may allow for the most efficient assessment of short-term respiratory-mediated autonomic
oscillations.(42)
To mitigate these difficulties, the simplest way to analyse acute / immediate effects of different

YM, Vol. XLIV No. 3 193 Bhavanani (2012)
HRV AS A RESEARCH TOOL IN YOGA
Yoga techniques seems to be to do the HRV recordings only before and after the selected
manoeuvres and earlier works on HRV and Pr¡¸¡y¡ma have done so(7, 27, 28). Two recent studies(30,
34) tried to analyse HRV during Pr¡¸¡y¡ma and finally concluded that such an analysis couldn't
be done due to the changes in breathing frequency and patterns.
Another difficulty in doing acute / immediate studies on Yoga techniques such as Ësanas is
that there are postural changes involved in most of them. This is relevant as Kotani et al., have
concluded that the postural change associated with an altered autonomic balance affects not only
the amplitude of RSA, but also the phases of RSA and BP variations in a complicated manner. (43)
They noted note that the phase of the DBP waveform in the sitting position largely differs from
that in the standing position, which is caused by the factor that RSA changes the diastolic duration
that is sufficiently large to alter the cardiovascular regulation. This seems to be a major difficulty
in acute/immediate studies on inverted techniques such as Sarvangasana(44) or Sirsasana(11). It is
also important to remember that any of these dramatic changes in body position can influence the
SVB and that a short period of rest may be required in between repeat assessments after such
dramatic position changes. Dantas et al., have reported modifications in all parameters in time
and frequency domains due to increased sympathetic activity and decreased parasympathetic
activity when their subjects changed from supine to orthostatic position. (45)
Many of the breathing practices as well as concentrative-contemplative-meditative and re-
laxation techniques of Yoga, involve mental imagery and visualization with conscious aware-
ness as well as the intonation of audible sounds as part of N¡da Yoga. This may interfere with
HRV analysis as it has been reported that simple free talking, reading aloud and mental arithme-
tic result in marked LF predominance that may mistakenly be interpreted as due to sympathetic
activation.(41) The slowing of breathing per se generates a confounding effect on the RR spec-
trum, by bringing respiratory sinus arrhythmia (a predominantly vagal effect) into the non-respi-
ratory LF, thought (simplistically) to reflect sympathetic activity. These results have practical
relevance in the analysis and interpretation of Holter electrocardiograms using HRV techniques
as, in the absence of simultaneous analysis of respiration, changes in LF/HF ratio should not be
taken as clear evidence of changes in autonomic tone.(41) Despite these observations it is interest-
ing to note that exactly a year later, Bernardi et al., studied the recitation of the rosary, and also
of Yoga mantras, reporting that they both slowed respiration to almost exactly 6/min, and en-
hanced HRV and baroreflex sensitivity by synchronizing inherent cardiovascular rhythms.(15)
The above limitations take on a new dimension when we realize that most of the acute and
immediate studies on various types of meditation have been actually done during meditation.(12,

YM, Vol. XLIV No. 3 194 Bhavanani (2012)
HRV AS A RESEARCH TOOL IN YOGA
16, 18, 19, 22, 23, 24, 25) However Hamada et al., have suggested that specific correlated relationships
exist between changes in autonomic nervous activity and EEG power depending on the differ-
ence in mental task, whether meditation or mental arithmetic.(46) They have also pointed out that
autonomic nervous activity during meditation is characterized by decreased sympathetic activ-
ity and increased parasympathetic activity while mental arithmetic tasks induce an enhanced
sympathetic activity.
CONCLUSION
A wide range of studies have reported HRV analyses of immediate, short and long term
effects of Yoga and its different techniques. While the majority gives evidence of enhanced
parasympathetic activity and decreased sympathetic activity with improved SVB; a few strike a
discordant note. Individual techniques are seen to have different effects as evidenced in acute
studies on forced uninostril breathing and Kap¡labh¡ti / high frequency Yogic breathing. The
tools of HRV analysis are highly sensitive to various factors such as the frequency of breathing,
vocalization, mental activities and physical posture and hence have limitations with regard to
Yoga studies. Innovative thoughts and novel methods need to be developed and applied if we are
to understand the intrinsic effects of this ancient art and science that is as relevant today as it was
millennia ago.
Total studies 33
(Retrieved from a Pubmed search of the terms HRV and Yoga, HRV and
Pr¡¸¡y¡ma, HRV and breathing, HRV and meditation, HRV and relaxation)
Year of study One study in 1991 and 1 in each year from 1997 to 2000. One study each in
2002, 2005 and 2009 and 2 studies each in 2001, 2004, 2007, and 2009. Four
studies each in 2008, 2010 and 2012 and 5 studies in 2011.
Duration of Acute / immediate studies 21 Ranging from 2, 5, 10 and 30 minutes
study of different techniques to overnight
sleep studies
Effect of training 11 Training duration ranging from 2, 5 and
8 days, 20 classes, 5, 6 and 10 weeks as
well as 4 months and 1 year.
Technique Ësana1 1 á¢rÀ¡sana
studied Pr¡¸¡y¡ma 8 Kap¡labh¡ti, N¡·¢ áuddhi, right and
left uninostril and alternate nostril
breathing techniques.

YM, Vol. XLIV No. 3 195 Bhavanani (2012)
HRV AS A RESEARCH TOOL IN YOGA
Relaxation 3 DRT, áavasan, others
Various types of 13 Cyclic, Zen, Ku¸·alin¢,
meditation / chanting/ Chi meditation, loving-kindness
N¡da Yoga meditation, nondirective meditation and
rosary/ Mantra chanting
Combination practices 7 Ësana, Pr¡¸¡y¡ma, relaxation,
meditation
Others techniques 1 Integrative body-mind training
Subject Normal/healthy volunteers 29 Age groups ranging from school /
population college students to elderly subjects in
both genders
Special populations 4 One each in pregnancy, smokers on
cessation programme, depression and
post traumatic stress syndrome
Major Improvement of HRV/ 23 Eight studies of combination practices,
conclusions SVB / increased 12 of meditation/chanting,
parasympathetic/ 2 with relaxation techniques and 1 each
decreased sympathetic of slow Pr¡¸¡y¡ma and integrative
body-mind training
Sympathetic enhancement 5 One of á¢rÀ¡sana and 3 of Kap¡labh¡ti
/ high frequency yogic breathing. The
other one was a comparison between
subjects who had a year of Yoga and
controls
Blunting of sympathetic 1 Subjects trained in combination
response practices
No significant changes as 3 One in áavasana relaxation and 2 in
compared to controls or comparative study of uninostril and
between techniques alternate nostril pr¡¸¡y¡ma techniques
Other reported findings 1 Increase in stochastic nature and
decrease in nonlinear nature of signal
during Chi meditation with decrease in
degree of nonlinearity and stochastic
nature during Ku¸·alin¢ meditation.

YM, Vol. XLIV No. 3 196 Bhavanani (2012)
HRV AS A RESEARCH TOOL IN YOGA
REFERENCES
1. Innes K. E., Bourguignon C., Taylor A. G. (2005), Risk indices associated with the insulin
resistance syndrome, cardiovascular disease, and possible protection with yoga: a systematic
review. J Am Board Fam Pract; 18: 491-519.
2. Madanmohan, Bhavanani A. B., Prakash E. S., Kamath M. G., Amudhan J. (2004), Effect
of six weeks of shavasan training on spectral measures of short term heart rate variability in
young healthy volunteers. Indian J Physiol Pharmacol; 48:370-3.
3. Terathongkum S., Pickler, R. H. (2004), Relationships among heart rate variability,
hypertension, and relaxation techniques. Journal of Vascular Nursing; 22: 78-82.
4. Streeter C. C., Gerbarg P. L., Saper R. B., Ciraulo D. A., Brown R. P. (2012), Effects of
yoga on the autonomic nervous system, gamma-aminobutyric-acid, and allostasis in epilepsy,
depression, and post-traumatic stress disorder. Med Hypotheses; 78: 571-9.
5. Stancák A. Jr, Kuna M., Srinivasan, Vishnudevananda S., Dostálek C. (1991), Kapalabhati
yogic cleansing exercise. I. Cardiovascular and respiratory changes. Homeost Health Dis ;
33: 126-34.
6. Bowman A. J., Clayton R. H., Murray A., Reed J. W., Subhan M. M., Ford G. A. (1997),
Effects of aerobic exercise training and yoga on the baroreflex in healthy elderly persons.
Eur J Clin Invest; 27: 443-9.
7. Raghuraj P., Ramakrishnan A. G., Nagendra H. R., Telles S. (1998), Effect of two selected
yogic breathing techniques of heart rate variability. Indian J Physiol Pharmacol; 42:467-72.
8. Bernardi L., Passino C., Wilmerding V., Dallam G. M., Parker D. L., Robergs R. A.,
Appenzeller O. (2001), Breathing patterns and cardiovascular autonomic modulation during
hypoxia induced by simulated altitude. J Hypertens 2001;19:947-58.
9. Vempati R., Telles S. (2000), Baseline occupational stress levels and physiological responses
to a two day stress management program. J Indian Psychol; 18: 33-7.
10. Vempati R. P., Telles S. (2002), Yoga-based guided relaxation reduces sympathetic activity
judged from baseline levels. Psychol Rep; 90: 487-94.
11. Manjunath N.K., Telles S. (2003), Effects of sirsasana (headstand) practice on autonomic
and respiratory variables. Indian J Physiol Pharmacol; 47: 34-42.
12. Reddy L.R., Kuntamalla S. (2011), Analysis of degree of nonlinearity and stochastic nature
of HRV signal during meditation using delay vector variance method. Conf Proc IEEE Eng
Med Biol Soc:2720.

YM, Vol. XLIV No. 3 197 Bhavanani (2012)
HRV AS A RESEARCH TOOL IN YOGA
13. Libby D. J., Worhunsky P. D., Pilver C. E., Brewer J. A. (2012), Meditation-induced changes
in high-frequency heart rate variability predict smoking outcomes. Front Hum Neurosci;
6:54.
14. An H., Kulkarni R., Nagarathna R., Nagendra H. (2010), Measures of heart rate variability
in women following a meditation technique. Int J Yoga;3:6-9.
15. Bernardi L., Sleight P., Bandinelli G., Cencetti S., Fattorini L., Wdowczyc-Szulc J., Lagi
A. (2001), Effect of rosary prayer and yoga mantras on autonomic cardiovascular rhythms:
comparative study. BMJ; 323:1446-9.
16. Kemper K. J., Shaltout H. A. (2011), Non-verbal communication of compassion: measuring
psychophysiologic effects. BMC Complement Altern Med;11:132.
17. Melville G. W., Chang D., Colagiuri B., Marshall P.W., Cheema B. S. (2012), Fifteen
minutes of chair-based yoga postures or guided meditation performed in the office can
elicit a relaxation response. Evid Based Complement Alternat Med: 501986.
18. Murata T., Takahashi T., Hamada T., Omori M., Kosaka H., Yoshida H., Wada Y. (2004),
Individual trait anxiety levels characterizing the properties of zen meditation.
Neuropsychobiology; 50:189-94.
19. Nesvold A., Fagerland M. W., Davanger S., Ellingsen O., Solberg E. E., Holen A., Sevre
K., Atar D. (2011) Increased heart rate variability during nondirective meditation. Eur J
Cardiovasc Prev Rehabil; Jun 21. [Epub ahead of print]
20. Patra S., Telles S. (2010), Heart rate variability during sleep following the practice of cyclic
meditation and supine rest. Appl Psychophysiol Biofeedback; 35: 135-40.
21. Peng C. K., Mietus J. E., Liu Y., Khalsa G., Douglas P. S., Benson H., Goldberger A. L.
(1999), Exaggerated heart rate oscillations during two meditation techniques. Int J
Cardiol; 70:101-7.
22. Peressutti C., Martín-González J. M., M García-Manso J., Mesa D. (2010), Heart rate
dynamics in different levels of Zen meditation. Int J Cardiol;145:142-6.
23. Phongsuphap S., Pongsupap Y., Chandanamattha P., Lursinsap C. (2008), Changes in heart
rate variability during concentration meditation. Int J Cardiol;130:481-4.
24. Tang Y. Y., Ma Y., Fan Y., Feng H., Wang J., Feng S., Lu Q., Hu B., Lin Y., Li J., Zhang
Y., Wang Y., Zhou L., Fan M. (2009), Central and autonomic nervous system interaction is
altered by short-term meditation. Proc Natl Acad Sci U S A; 106: 8865-70.
25. Wu S. D., Lo P. C. (2008) Inward-attention meditation increases parasympathetic activity:
a study based on heart rate variability. Biomed Res; 29: 245-50.

YM, Vol. XLIV No. 3 198 Bhavanani (2012)
HRV AS A RESEARCH TOOL IN YOGA
26. Chaya M. S., Ramakrishnan G., Shastry S., Kishore R. P., Nagendra H., Nagarathna R., Raj
T., Thomas T., Vaz M., Kurpad A. V. (2008), Insulin sensitivity and cardiac autonomic
function in long term practitioners of yoga. Natl Med J India; 21: 215-6.
27. Ghiya S., Lee C. M. (2012), Influence of alternate nostril breathing on heart rate variability
in non-practitioners of yogic breathing. Int J Yoga; 5:66-9.
28. Jovanov E. (2005), On Spectral Analysis of Heart Rate Variability during Very Slow Yogic
Breathing. Conf Proc IEEE Eng Med Biol Soc; 3: 2467-70.
29. Khattab K., Khattab A. A., Ortak J., Richardt G., Bonnemeier H. (2007), Iyengar yoga
increases cardiac parasympathetic nervous modulation among healthy yoga practitioners.
Evid Based Complement Alternat Med; 4: 511-7.
30. Raghuraj P., Telles S. (2008), Immediate effect of specific nostril manipulating yoga
breathing practices on autonomic and respiratory variables. Appl Psychophysiol Biofeedback;
33: 65-75.
31. Santaella D. F., Devesa C. R., Rojo M. R., Amato M. B., Drager L. F., Casali K. R., Montano
N., Lorenzi-Filho G. (2011), Yoga respiratory training improves respiratory function and
cardiac sympathovagal balance in elderly subjects: a randomised controlled trial. BMJ
Open;1:e000085.
32. Satyapriya M., Nagendra H. R., Nagarathna R., Padmalatha V. (2009), Effect of integrated
yoga on stress and heart rate variability in pregnant women. Int J Gynaecol Obstet; 104:
218-22.
33. Shapiro D., Cook I. A., Davydov D. M., Ottaviani C., Leuchter A. F., Abrams M. (2007),
Yoga as a Complementary Treatment of Depression: Effects of Traits and Moods on
Treatment Outc me. Evid Based Complement Alternat Med; 4: 493-502.
34. Telles S., Singh N., Balkrishna A. (2011), Heart rate variability changes during high
frequency yoga breathing and breath awareness. Biopsychosoc Med; 5: 4.
35. Telles S., Singh N., Joshi M., Balkrishna A. (2010), Post traumatic stress symptoms and
heart rate variability in Bihar flood survivors following yoga: a randomized controlled study.
BMC Psychiatry; 10 : 18.
36. Wolever R. Q., Bobinet K. J., McCabe K., Mackenzie E. R., Fekete E., Kusnick C. A.,
Baime M. (2012), Effective and viable mind-body stress reduction in the workplace: a
randomized controlled trial. J Occup Health Psychol; 17: 246-58.
37. Madanmohan, Prakash E. S., Bhavanani A. B. (2005), Correlation between short-term heart
rate variability indices and heart rate, blood pressure indices, pressor reactivity to isometric
handgrip in healthy young male subjects. Indian J Physiol Pharmacol; 49: 132-8.

YM, Vol. XLIV No. 3 199 Bhavanani (2012)
HRV AS A RESEARCH TOOL IN YOGA
38. Rajajeyakumar M, Madanmohan, Amudharaj D., Bandi Harikrishna, Jeyasettiseloune,
Bhavanani A. B. (2011), Immediate effect of suryanadi and chandranadi on short term heart
rate variability in healthy volunteers. Indian J Physiol Pharmacol; 55 (5 supplement): 43-44.
39. Hari Krishna B., Madanmohan, Balachander J., Jayasettiaseelon E., Bhavanani A. B. (2012),
Immediate effect of Shavasanaa on short term heart rate variability in heart failure patients.
Abstracts of the International Conference on Cardiovascular Research Convergence.
February; AIIMS, New Delhi. Pg 141.
40. Brown T. E., Beightol L. A., Koh J., Ekberg D. L. (1993), Important influence of respiration
on human R-R interval power spectra is largely ignored. J Appl Physiol; 75: 2310-7.
41. Bernardi L., Wdowczyk-Szulc J., Valenti C., Castoldi S., Passino C., Spadacini G., Sleight
P. (2000), Effects of Controlled Breathing, Mental Activity and Mental Stress With or
Without Verbalization on Heart Rate Variability. J Am Coll Cardiol;35:1462-9.
42. Cooke W. H., Cox J. F., Diedrich A. M., Taylor J. A., Beightol L. A., Ames J. E. 4th, Hoag
J. B., Seidel H., Eckberg D. L. (1998), Controlled breathing protocols probe human autonomic
cardiovascular rhythms. Am J Physiol; 274: H709-18.
43. Kotani K., Takamasu K., Jimbo Y., Yamamoto Y. (2008), Postural-induced phase shift of
respiratory sinus arrhythmia and blood pressure variations: insight from respiratory-phase
domain analysis. Am J Physiol Heart Circ Physiol; 294: H1481-9.
44. Konar D., Latha R., Bhuvaneswaran J. S. (2000), Cardiovascular responses to head-down-
body-up postural exercise (Sarvangasana). Indian J Physiol Pharmacol; 44:392 400.
45. Dantas E. M., Gonçalves C. P., Silva A. B., Rodrigues S. L., Ramos M. S., Andreão R.
V., Pimentel E. B., Lunz W., Mill J. G. (2010), Reproducibility of heart rate variability
parameters measured in healthy subjects at rest and after a postural change maneuver. Braz
J Med Biol Res; 43: 982-8.
46. Hamada T., Murata T., Takahashi T., Ohtake Y., Saitoh M., Kimura H., Wada Y., Yoshida
H. (2006), Changes in autonomic function and EEG power during mental arithmetic task
and their mutual relationship. Rinsho Byori; 54: 329-34.