Pranayama: the art and science of breathing
Thousands of years ago the holistic science of yoga originated in India. Today, an increased awareness about health and natural remedies has brought many people closer to yoga and pranayama, which have been proven to be effective methods for improving health, either by preventing or management of many diseases.
A growing body of research supports the belief that yoga may improve physical and mental health through down‐regulation of the hypothalamus pituitary adrenal (HPA) axis and the sympathetic nervous system. (The flight or fight response) See more on how this system affects our moods in this video.
Yoga is extensively reported to reduce stress and anxiety and its effectiveness against stress management is well established. 
Pranayama: the extension of the life-force
Pranayama is generally defined as breath control. Although this interpretation may seem correct in view of the practices involved, it does not convey the full meaning of the term.
The word pranayama is comprised of two roots: ‘prana‘ and ‘ayama‘.
Prana means vital energy or life force. It is the force which exists in all things, whether animate or inanimate. Although closely related to the air we breathe, it is more subtle than air or oxygen. Therefore, pranayama should not be considered as mere breathing exercises aimed at introducing extra oxygen into the lungs. Pranayama utilises breathing to influence the flow of prana in the nadis or energy channels (nerves).
The word Ayama is defined as extension, expansion, length, stretch or restrain.
Thus, the word pranayama means ‘extension or expansion of the dimension of prana and its control‘. , 
When the prana in the body is low, one tends to be more lethargic, dull, and unenthusiastic. Toxins then accumulate in the body and pain, stiffness or disease set in. Through the practice of yoga and pranayama, prana begins to flow, allowing toxins to be released and removed.
According to yoga knowledge, the body is just a gross form of the mind. Body and mind are not separate entities and every mental knot has a corresponding physical knot in the body and vice versa and the breath is the bridge that connects body and mind.
Yoga means union and the aim of yogic practices is to release these knots and to connect us with the joy, love, and creativity, integrating, and harmonising the body and mind.
A natural result of going deep into pranayama is clarity, steadiness and one‐pointedness of the mind. , 
The importance of a correct breathing
The breath is the most vital process of the body. It influences every cells’ activity and, most importantly, is intimately linked with the performance of the brain.
Respiration fuels the burning of oxygen and glucose, producing energy to power every muscular contraction, glandular secretion and mental process.
In modern society, most people breathe incorrectly, using only a small part of their lung capacity.
Irregular breathing disrupts the rhythms of the brain and leads to physical, emotional and mental blocks. These bring about inner conflicts, an unbalanced personality, a disordered lifestyle and diseases.
Pranayama establishes regular breathing patterns, breaking this negative cycle and reversing the debilitating process. It does so by giving us control of the breath and re-establishing the natural, relaxed rhythms of the body and mind.
Observing nature, it’s straightforward to understand that animals with a slow breath rate such as elephants and tortoises have long life spans, whereas those with a fast breathing rate such as birds, dogs and rabbits live for only a few years. From simple but wise observations like these, ancient yogis realised the importance of slow breathing for increasing the human lifespan.
On the physical level, this happens because the respiration is directly related to the heart. A slow breathing rate keeps the heart stronger and better nourished and contributes to a longer life. 
Mr. B.K.S. Iyengar in his book Light on Yoga says: “The yogi’s life is not measured by the number of his days, but by the number of his breaths. Therefore, he follows the proper rhythmic patterns of slow deep breathing. These rhythmic patterns strengthen the respiratory system, soothe the nervous system and reduce craving.” 
Today, breathing techniques are increasingly being used for therapeutic purposes, and research suggests that pranayama may be especially helpful in managing hypertension (a disease affecting more than 1 billion people worldwide). Check out our article on Yoga & Hypertension here.
Sukha pranayama (a simple type of yogic breathing that is done by consciously regulating the inhalation and exhalation to an equal ratio) at the rate of 6 breaths/minute can reduce heart rate and blood pressure in hypertensive patients within 5 minutes of practice. 
Bhramari or Humming Bee is another safe and effective breathing practice to calm the nerves and relax the mind. You can lear how to perform it, check out our video.
Right Nostril Breathing Versus Left Nostril Breathing
Ancient yogis discovered what scientists today refer to as the nasal cycle.
In fact, the airflow through the nasal passage is normally asymmetrical, with one nasal passage having the dominant airflow. This asymmetry of nasal airflow is not fixed, as the dominant airflow alternates from one nasal passage to the other. 
Humans and other animals cycle alternatively from breathing through one nostril to the other over periods ranging from a few minutes to a few hours, even during sleep.
More and more scientific research is supporting the notion that breathing through different nostrils has different effects in the body.
Right Nostril Breathing
Left Nostril Breathing
Yogis compared the effects of left nostril breathing, right nostril breathing and breathing through both nostril simultaneously.
According to yogic culture, the left nostril is connected to Ida, an energy pathway that travels alongside the spine which is cooling, restorative and feminine in nature.
The right nostril is governed by the Pingala, which is warming, energising, and masculine.
Nadi Sodhana or Alternate Nostril Breathing is a very safe pranayama technique which balances the sympathetic and parasympathetic branches of the autonomic nervous system.
Masters believe that during meditation the breath should be evenly through the two nostrils.
Nadi Shodhana, because of its balancing effects, is considered the perfect prelude to meditation. 
You can learn how to safely practice Nadi Shodhana or Alternate Nostril Breathing in this video.
Effects of breathing, inhalation, exhalation and retention of breath on the body
Inhalation Vs. Exhalation
|Inhalation tends to be cooling|
|Exhalation tends to be heating|
Retention of Breath
|Retention after inhalation is heating|
|Retention after exhalation is cooling|
|During inhalation we take air in, which has a cooling effect. During retention air is digested and this creates heat. That heat is directed and dispersed upon exhalation so holding the breath is generally heating. However, holding the breath after exhalation becomes cooling.|
Right Nostril Vs. Left Nostril Breathing
|Right nostril breathing is heating and stimulating||Left nostril breathing is cooling and sedating|
|Right nostril breathing increases the flow through channels (nerves) and organs on the right side of the body. Stimulating these increases heat in the body and promotes all thermogenic processes like digestion.|
Left nostril breathing increases the flow through channels (nerves) and organs on the left side of the body. Stimulating these increases cold in the body and promotes all consolidating processes in the body like tissue formation and stabilisation.
This is the basis of Alternate Nostril Breathing (Nadi Shodhana) that is perhaps the most important and cleansing of the pranayamas.
However, mouth breathing generally increases mucus and should be only be done for shorts periods of time, mainly on exhalation.
Nose Breathing Vs. Mouth Breathing
|Breathing through the nose is heating||Breathing through the mouth tends to be cooling||Mouth breathing can be used to release heat.|
Fast Breathing Vs. Slow Breathing
|Fast breathing is heating|
|Slow breathing is cooling|
A strong yoga physical practice, however useful in itself, is not the real goal of yoga practice.
As yoga practice advances it is meant to take us deeper into our own minds and hearts.
An advanced yogi should be an enlightened person, not simply someone who is very flexible or able to hold difficult asanas for long periods.
As any yoga practitioner advances in his/her practice, it is important to remember the deeper aspects of yoga such as pranayama, mantra (chanting) and meditation. After mastering of the body has been achieved, aim at mastering the mind as well.
Asanas (physical postures) should be used as a foundation for developing a deeper yoga practice. 
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 Iyengar, B. K. S. (2011). The illustrated light on yoga. Harper Element. pag. 24-25
 Bhavanani, A. B., Sanjay, Z., & Madanmohan. (2011). Immediate effect of sukha pranayama on cardiovascular variables in patients of hypertension. International journal of yoga therapy, 21(1), 73-76.