(1) Amit Sood, MD , (2)Brent A. Bauer, MD

1. Amit Sood, MD, Department of Medicine, Mayo Clinic College of Medicine
2. Brent A. Bauer, MD, Department of Medicine, Mayo Clinic College of Medicine

Correspondence:

Amit Sood, MD
Department of Medicine
Baldwin 4^th floor
Mayo Clinic College of Medicine
Rochester, MN 55905

Email – sood.amit@mayo.edu

 Abstract

Yogic breathing practices also called Pranayamas originated several thousand years ago and are now practiced all over the world.   However, it is only in the last two decades that considerable advances in our understanding of the physiologic principles behind these practices have been made.  This has been accomplished using modern electrophysiologic and imaging techniques including functional MRI and PET scanning.  In this article we will present an evidence-based review of the physiologic effects of yogic breathing practices.

Introduction

In the yogic philosophy, breath control is considered one of the essential early steps towards progress in yoga and meditation.  This is believed to be accomplished by practicing breathing techniques called Pranayamas.   Pranayamas were developed several thousand years ago, at a time when the current diagnostic and imaging modalities were not available.  Data about the potential benefit from Pranayamas was largely anecdotal and not evidence based.  In the last two decades, considerable advances in our understanding of the physiological basis of Pranayama techniques have been made using sophisticated electrophysiologic and imaging studies.  This article will review some of the pertinent physiologic data on Pranayamas.

What are Pranayamas

In Sanskrit, an ancient Indian language, the word Prana means breath and also life energy.  Pranayama traditionally means control of Prana or breath.   The more subtle meaning however is expansion of the Prana and not merely its control.  Control of breathing has both voluntary and involuntary components in human beings.  Breath is thus believed to serve as a gateway between the conscious and sub-conscious components of our mind.  A harmonious breathing process is believed to be central to good health and well being.  Yoga masters believe that by breath control, one can achieve expansion of the Prana, and thereby a higher state of consciousness.

The practice of Pranayamas depends on an ability to control our breathing by volition.  The four phases of respiration i.e. inhalation, internal breath retention, exhalation and external breath retention can all be voluntarily controlled.  Initial steps in Pranayama training involve control of inhalation and exhalation.  Advanced practices are built on these basic steps.

Neural pathways involved in voluntary breath control

 Since voluntary breath control is the central component of Pranayamas it will be helpful to first understand the neuro-physiology of the process of voluntary breath control.  We exercise breath control in several daily activities including speech, singing, and playing musical instruments.  Electrical stimulation of brain structures in cats, dogs, monkeys, and humans (during brain surgery) suggest a widespread distribution of the cortical and subcortical sites involved in this process ¹.

Volitional inspiration is associated with an increase in signal in the superior motor cortex, premotor cortex and supplementary motor area on functional MRI imaging ².  Additional brain regions activated with volitional inspiration include inferolateral sensorimotor cortex, prefrontal cortex and striatum.   Stimulation of superolateral motor cortex by transcranial magnetic stimulation is shown to cause contralateral diaphragmatic contraction ^{3, 4}.  Activation of the premotor cortex and supplementary motor area generally correlates with successful execution of several voluntary movements ^{5, 6}.  Thus, several brain areas are simultaneously activated to coordinate the complex function of volitional inspiration.

Volitional breath holding is associated with an overall increase in cerebral blood flow, primarily to the gray matter ⁷.  Breath holding leads to an increase in arterial carbon dioxide level and this in turn, along with lowering of the pH, mediates vasodilatation.  These changes are most prominent at end expiration.  The higher arterial carbon dioxide level and acidosis explains greater difficulty with breath holding at end expiration compared to end inspiration.

Our understanding of the CNS mechanisms involved in voluntary breath control is however still primitive.  Future studies focussing on the effect of Pranayama techniques on cerebral blood flow and substrate utilization will better clarify how our brain operates during these exercises.  An accurate description of the neuro-physiology associated with Pranayamas will likely remove some ignorance and mysticism associated with these techniques.

Place of Pranayama in Yogic way of life

Sage Patanjali laid out the Eight steps of Yoga around 300 BC.  They are grouped into 3 main categories:

A. Yogic way of life:

1.  Yamas – Right conduct towards others.

2.  Niyamas – Right conduct towards oneself.

B. External Yogic practices:

1.  Aasanas – Physical postures and exercises

2.  Pranayamas – Breath (life force) control

3.  Pratyahaara – Control of mind and sensory organs

C. Internal Yogic practices:

1.  Dhaarana – Concentration and focussed attention

2.  Dhyaana – Meditation

3.  Samadhi – Salvation or achievement of perfection

Progress in yoga is believed to be a slow step by step process with a disciplined approach being the key to achieve the desired goals.  Successful mastery of the earlier steps is helpful, and sometimes necessary to advance to the next level.  Thus yoga masters believe that without following a yogic way of life with right conduct towards others and self, it will be difficult to obtain full benefits from regular practice of yogic exercises or Pranayamas.

Physiologic correlates of Individual Pranayama techniques

Several of the Pranayama practices have been studied using modern electrophysiologic and imaging techniques.  Evidence based literature pertinent to the commonly practiced Pranayamas is summarized below.

Breath awareness:  Using this technique participants are introduced to their own breathing patterns and respiratory system.  They are taught to become consciously aware of the flow of their breath.  The process of learning breath awareness itself leads to relaxation and helps one attain slow and regular breathing ⁸ and thereby reduced sympathetic activity ⁹.

Relaxation response increases cardiac parasympathetic tone both by slow breathing ¹⁰ and

also independent of a change in respiratory rate ¹¹.  Paced slow breathing has been shown to reduce anxiety in alcoholics ¹².  A practice of slow deep breathing 10 minutes a day with the help of a device is shown to reduce systolic blood pressure by up to 5 mm hg in controlled clinical trials ¹³.   Thus, a practice of breath awareness is likely to have a calming effect by several mechanisms.

Abdominal (diaphragmatic) breathing:  Abdominal breathing involves selectively using the

diaphragmatic muscles for inspiration.  This results in increased ventilation of the lower lobes of the lungs.  Deep abdominal breathing is associated with improved alveolar recruitment, improved matching of ventilation and perfusion and is shown to improve oxygenation after just 30 breaths ¹⁴.   Shallow diaphragmatic movement increases the risk of atelectasis and pneumonias ¹⁵.   Practicing deep abdominal breathing reduces systolic and diastolic blood pressure ¹⁶ and is also shown to reduce anxiety in healthy volunteers ¹⁷, and dental surgery patients ¹⁸.  Thus, deep abdominal breathing is likely to help long term general health and improve pulmonary function.

Thoracic breathing:  Deep thoracic breathing involves using the chest wall muscles as the

primary muscles of inspiration.  This is helpful in expansion of the upper and middle lobes of the lungs and tones up and strengthens the inspiratory muscles.

 Yogic breathing:  The term yogic breathing is often mistakenly considered synonymous with

all the Pranayamas.  However, yogic breathing actually is just one type of Pranayama that involves a combination of abdominal and thoracic breathing as described above.  Yogic breathing is reported to reduce free radicals and improve Superoxide dismutase (anti-oxidant) levels in the blood ¹⁹.   All the benefits of diaphragmatic breathing are likely to be obtained with the yogic breathing.  The slow and deep yogic breathing has also been shown to be of benefit by increasing baroreceptor sensitivity, increased heart rate variability, and lower peripheral vascular tone resulting in sustained vasodilatation ²⁰.

Alternate nostril breathing (Nadi Shodhan Pranayama):  Alternate nostril breathing is one of

the most important and best described Pranayama.  In this exercise, participants learn a systematic program of alternate nostril breathing with slow deep regular respiration.  The duration of pause after inspiration and the duration of expiration are each twice the amount of time spent in inspiration.  The physiology of alternate nostril breathing is best understood by first discussing the cerebral and nasal cycles.

Ultradian rhythm also called the cerebral cycle, is the rhythm of alternating cerebral dominance that is seen in humans and other mammals during waking and sleep ²¹.   Nasal rhythm is a nasal cycle of congestion-decongestion of alternate nasal mucosa.  Ultradian and nasal rhythm are closely coupled.   The predominant airflow in one of the nostrils at a given time correlates with activation of the contralateral cerebral cortex.  The periodicity of these cycles ranges from 20 to 200 minutes ²².  Relatively greater EEG amplitudes are seen in the cerebral hemisphere contralateral to the active nostril ²³.   Unilateral forced nostril breathing also correlates with greater cognitive ability in the contralateral hemisphere ²⁴.   An altered breathing pattern is thus shown to influence the cognitive performance ²¹.

Forced alternate nostril breathing (FANB) is associated with a decrease in hemisphere asymmetry in the b-1 band on the EEG.  FANB is shown to have a balancing effect on the functional activity of the left and right cerebral hemispheres ²⁵.  Additionally, right unilateral forced nasal breathing (UFNB) is shown to increase sympathetic activity and left UFNB increases the parasympathetic activity ^{22, 26}.  These descriptions are similar to the experiential observations described by ancient sages in classical yoga texts that are believed to be several thousand years old.  UFNB is also reported to cause a significant change in intra-ocular pressure (IOP).  Right UFNB is reported to decrease IOP by as much as 25%.  On the other hand left UFNB is associated with a modest (4.5%) increase in IOP ²⁷.

Several simple maneuvers can be tried to influence the flow of breath in one nostril. Changing from an erect to a supine position leads to a general nasal congestion on both the sides.  Assuming a lateral supine position causes congestion in the nasal mucosa on the dependent side with airflow starting on the non-dependent side in a short time.  Unilateral axillary pressure leads to ipsilateral nasal congestion and contralateral decongestion ²⁸.  If controlled trials of UFNB show physiologic benefits in specific diseases, these techniques would be valuable to direct the flow of breath through a specific nostril.

According to the yogic literature, the aim of practicing alternate nostril breathing Pranayama is to balance the flow of air in the two nostrils and thereby balance the autonomic nervous system.  Based on the evidence given earlier, it might be reasonable to conclude that achieving an optimal airflow in the two nostrils could balance the activity of the sympathetic and parasympathetic nervous and activation of the two cerebral hemispheres.  This conclusion obtained using data from recent scientific experiments bears striking resemblance to the descriptions of Pranaymas in ancient texts.

Humming bee breath (Bhramari Pranayama):   In the humming bee breath technique,

participants learn to create a vibratory sound in their head and sinuses during a prolonged expiration.  After some practice, this sound may resemble that of a bee gently humming.

Humming is shown to release Nitrous oxide (NO), an endogenous vasodilator from the paranasal sinuses into the nasal mucosa ^{29, 30}.  Paranasal sinuses act as rich reservoirs of NO ³¹.  NO plays a role in the balance between the negative inspiratory force and pharyngeal dilators ³².  In patients with sleep apnea, there is reduced ability to transport NO to the pulmonary parenchyma.  Blockade of endogenous NO production is shown to result in moderate hypertension in healthy volunteers ³³.  Endothelium derived NO regulates basal pulmonary and systemic vascular tone ³⁴.  NO also regulates ventilation – perfusion matching in the lungs.  It is thus plausible that humming bee breath may favorably influence hemodynamics by increasing pulmonary and / or systemic NO levels.

 

The other aspect of humming bee breath involves slow expiration with vibration of the vocal cords and soft palate.  The benefits of slow and deep breathing have been discussed above and fully apply to humming bee breath Pranayama.

 

Psychic breath (Ujjayi Pranayama):  Psychic breathing practice entails breathing slowly ‘through the throat’, creating a gentle sound like that of a sleeping baby. The breathing pattern associated with Ujjayi Pranayama demonstrably slows the metabolic rate and thereby oxygen consumption ³⁵.  Additionally, the benefits of slow breathing are also obtained using this technique.

Yogic bellows breathing (Bhastrika Pranayamas):  Bellows breathing pattern is a rapid,

forceful non jerky breathing.  The specific pattern of breathing in this Pranayama is associated with decreased visual and auditory reaction time ³⁶.  Yogic bellows breathing is a stimulating Pranayama.  Thus patients with hypertension, cardiovascular or cerebrovascular ailments and epilepsy are advised against practicing this technique.  However, there is no evidence based data to support this recommendation.

 

Other Pranayamas:  Sheetali (cooling breath), Seetkari (hissing breath) and

Kapalbhati  – There is limited research data available about the efficacy or physiologic mechanisms of these three Pranayamas.

 

Clinical Implications:

Based on the physiologic evidence presented above, a systematic practice of Pranayamas could be incorporated as an adjunctive therapy in a number of medical conditions.  These include; hypertension, chronic respiratory disorders including asthma and COPD, anxiety, depression, cancer, chronic pain, irritable bowel syndrome, and ‘stress’.  Under the close supervision of an experienced yoga teacher, a well-developed, disease-specific program of Pranayamas is likely to promote relaxation, improve cardio-pulmonary function, reduce blood pressure, and result in an overall reduction of stress with improved quality of life.  Physicians should however caution patients that given a relative paucity of data from rigorous clinical trials, Pranayamas should generally not be considered as first line treatments for most diseases.  These exercises should be seen as useful and generally safe adjuncts, likely to facilitate a direct involvement of patients in their own care and thereby provide them with a sense of control and empowerment. 

 Conclusions:

 Pranayama means control and expansion of breath and life force.  The neuro-physiology behind voluntary control of breath is complex and incompletely understood.  There is however compelling physiologic data to suggest that slow, deep and regular breathing improves several hemodynamic and biochemical parameters.  The link between cerebral cycle, nasal cycle and autonomic tone needs to be explored further for future therapeutic potential.   Research in Pranayamas should focus on several disease targets that are likely to respond to the control of autonomic nervous system, pulmonary ventilation and vascular tone.  Finally, given a relative paucity of data from rigorous clinical trials, Pranayamas should generally not be considered as first line treatments for most diseases.

Acknowledgements: Authors thank the Lucy Gonda foundation for their generous support of this publication.

 

References

1.         Davenport PWR, R. L. Cerebral cortex and respiration. In: AI DJaP, ed. Regulation of Breathing. 2nd edn ed. New York: Marcel Dekker Inc.; 1995:365-388.

2.         Evans KC, Shea SA, Saykin AJ. Functional MRI localisation of central nervous system regions associated with volitional inspiration in humans. J Physiol. Oct 15 1999;520 Pt 2:383-392.

3.         Maskill D, Murphy K, Mier A, Owen M, Guz A. Motor cortical representation of the diaphragm in man. J Physiol. Nov 1991;443:105-121.

4.         Urban PP, Morgenstern M, Brause K, et al. Distribution and course of cortico-respiratory projections for voluntary activation in man. A transcranial magnetic stimulation study in healthy subjects and patients with cerebral ischemia. J Neurol. Jun 2002;249(6):735-744.

5.         Passingham R. The frontal lobes and voluntary action. Oxford Psychology Series. Vol 21. Oxford: Oxford University Press; 1993.

6.         Cunnington R, Windischberger C, Deecke L, Moser E. The preparation and execution of self-initiated and externally-triggered movement: a study of event-related fMRI. Neuroimage. Feb 2002;15(2):373-385.

7.         Kastrup A, Li TQ, Glover GH, Moseley ME. Cerebral blood flow-related signal changes during breath-holding. AJNR Am J Neuroradiol. Aug 1999;20(7):1233-1238.

8.         Telles S, Narendran S, Raghuraj P, Nagarathna R, Nagendra HR. Comparison of changes in autonomic and respiratory parameters of girls after yoga and games at a community home. Percept Mot Skills. Feb 1997;84(1):251-257.

9.         Vempati RP, Telles S. Yoga-based guided relaxation reduces sympathetic activity judged from baseline levels. Psychol Rep. Apr 2002;90(2):487-494.

10.       Sakakibara M, Hayano J. Effect of slowed respiration on cardiac parasympathetic response to threat. Psychosom Med. Jan-Feb 1996;58(1):32-37.

11.       Sakakibara M, Takeuchi S, Hayano J. Effect of relaxation training on cardiac parasympathetic tone. Psychophysiology. May 1994;31(3):223-228.

12.       Clark ME, Hirschman R. Effects of paced respiration on anxiety reduction in a clinical population. Biofeedback Self Regul. Sep 1990;15(3):273-284.

13.       Schein MH, Gavish B, Herz M, et al. Treating hypertension with a device that slows and regularises breathing: a randomised, double-blind controlled study. J Hum Hypertens. Apr 2001;15(4):271-278.

14.       Westerdahl E, Lindmark B, Eriksson T, Hedenstierna G, Tenling A. The immediate effects of deep breathing exercises on atelectasis and oxygenation after cardiac surgery. Scand Cardiovasc J. Dec 2003;37(6):363-367.

15.       Brooks-Brunn JA. Predictors of postoperative pulmonary complications following abdominal surgery. Chest. Mar 1997;111(3):564-571.

16.       Lee JS, Lee MS, Lee JY, Cornelissen G, Otsuka K, Halberg F. Effects of diaphragmatic breathing on ambulatory blood pressure and heart rate. Biomed Pharmacother. Oct 2003;57 Suppl 1:87s-91s.

17.       Peper E, MacHose M. Symptom prescription: inducing anxiety by 70% exhalation. Biofeedback Self Regul. Sep 1993;18(3):133-139.

18.       Biggs QM, Kelly KS, Toney JD. The effects of deep diaphragmatic breathing and focused attention on dental anxiety in a private practice setting. J Dent Hyg. Spring 2003;77(2):105-113.

19.       Bhattacharya S, Pandey US, Verma NS. Improvement in oxidative status with yogic breathing in young healthy males. Indian J Physiol Pharmacol. Jul 2002;46(3):349-354.

20.       Grossman A, Grossman E. [Treatment of hypertension with device-guided breathing exercise]. Harefuah. Oct 2003;142(10):677-679, 718.

21.       Shannahoff-Khalsa DS, Boyle MR, Buebel ME. The effects of unilateral forced nostril breathing on cognition. Int J Neurosci. Apr 1991;57(3-4):239-249.

22.       Werntz DA, Bickford RG, Bloom FE, Shannahoff-Khalsa DS. Alternating cerebral hemispheric activity and the lateralization of autonomic nervous function. Hum Neurobiol. 1983;2(1):39-43.

23.       Werntz DA, Bickford RG, Shannahoff-Khalsa D. Selective hemispheric stimulation by unilateral forced nostril breathing. Hum Neurobiol. 1987;6(3):165-171.

24.       Jella SA, Shannahoff-Khalsa DS. The effects of unilateral forced nostril breathing on cognitive performance. Int J Neurosci. Nov 1993;73(1-2):61-68.

25.       Stancak A, Jr., Kuna M. EEG changes during forced alternate nostril breathing. Int J Psychophysiol. Oct 1994;18(1):75-79.

26.       Shannahoff-Khalsa DS, Kennedy B. The effects of unilateral forced nostril breathing on the heart. Int J Neurosci. Nov 1993;73(1-2):47-60.

27.       Backon J, Matamoros N, Ticho U. Changes in intraocular pressure induced by differential forced unilateral nostril breathing, a technique that affects both brain hemisphericity and autonomic activity. A pilot study. Graefes Arch Clin Exp Ophthalmol. 1989;227(6):575-577.

28.       Babatola FD. Reciprocal changes in nasal resistance in response to changes in posture. Rhinology. Jun 1998;36(2):69-72.

29.       Weitzberg E, Lundberg JO. Humming greatly increases nasal nitric oxide. Am J Respir Crit Care Med. Jul 15 2002;166(2):144-145.

30.       Maniscalco M, Weitzberg E, Sundberg J, Sofia M, Lundberg JO. Assessment of nasal and sinus nitric oxide output using single-breath humming exhalations. Eur Respir J. Aug 2003;22(2):323-329.

31.       Andersson JA, Cervin A, Lindberg S, Uddman R, Cardell LO. The paranasal sinuses as reservoirs for nitric oxide. Acta Otolaryngol. Dec 2002;122(8):861-865.

32.       Haight JS, Djupesland PG. Nitric oxide (NO) and obstructive sleep apnea (OSA). Sleep Breath. Jun 2003;7(2):53-62.

33.       Albert J, Schedin U, Lindqvist M, Melcher A, Hjemdahl P, Frostell C. Blockade of endogenous nitric oxide production results in moderate hypertension, reducing sympathetic activity and shortening bleeding time in healthy volunteers. Acta Anaesthesiol Scand. Oct 1997;41(9):1104-1113.

34.       Stamler JS, Loh E, Roddy MA, Currie KE, Creager MA. Nitric oxide regulates basal systemic and pulmonary vascular resistance in healthy humans. Circulation. May 1994;89(5):2035-2040.

35.       Telles S, Desiraju T. Oxygen consumption during pranayamic type of very slow-rate breathing. Indian J Med Res. Oct 1991;94:357-363.

36.       Bhavanani AB, Madanmohan, Udupa K. Acute effect of Mukh bhastrika (a yogic bellows type breathing) on reaction time. Indian J Physiol Pharmacol. Jul 2003;47(3):297-300.