PRANAYAAMA -THE LIFE

Pranayama (Sanskrit: प्राणायाम prāṇāyāma) is a Sanskrit word meaning "extension of the prana or breath" or more accurately, "extension of the life force". The word is composed of two Sanskrit words, Prāna, life force, or vital energy, particularly, the breath, and "ayāma", to extend or draw out. (Not 'restrain, or control' as is often incorrectly translated from 'yama' instead of 'ayama').
Pranayama (Devanagari: प्राणायाम, prāṇāyāma) is a Sanskrit compound.
V. S. Apte provides fourteen different meanings for the word prana (Devanagari: प्राण, prāṇa) including these:

• Breath, respiration
• The breath of life, vital air, principle of life (usually plural in this sense, there being five such vital airs generally assumed, but three, six, seven, nine, and even ten are also spoken of)
• Energy, vigor
• The spirit or soul

Of these meanings, the concept of "vital air" is used by Bhattacharyya to describe the concept as used in Sanskrit texts dealing with pranayama. Thomas McEvilley translates "prana" as "spirit-energy". Its most subtle material form is the breath, but is also to be found in blood, and its most concentrated form is semen in men and vaginal fluid in women.
Monier-Williams defines the compound prāṇāyāma as (m., also pl.) "N. of the three 'breath-exercises' performed during Saṃdhyā (See pūraka, recaka, kumbhaka" This technical definition refers to a particular system of breath control with three processes as explained by Bhattacharyya: pūraka (to take the breath inside), kumbhaka (to retain it), and recaka (to discharge it). There are also other processes of pranayama in addition to this three-step model.
Macdonell gives the etymology as prāṇa + āyāma and defines it as "m. suspension of breath (sts. pl.)".
Apte's definition of āyāmaḥ derives it from ā + yām and provides several variant meanings for it when used in compounds. The first three meanings have to do with "length", "expansion, extension", and "stretching, extending", but in the specific case of use in the compound prāṇāyāma he defines āyāmaḥ as meaning "restrain, control, stopping".
An alternative etymology for the compound is cited by Ramamurti Mishra, who says that:

Expansion of individual energy into cosmic energy is called prāṇāyāma (prāṇa, energy + ayām, expansion).

Alternate nostril breathing (ANB) Pranyama also called Nadisuddhi pranyama is one of the beneficial Pranayama for cardiopulmonary functions. Regular practice of ANB (Nadisudhi) increases parasympathetic activity and lowers systolic blood pressure and Respiratory rate too.

Prana is a subtle invisible force. It is the life-force that pervades the body. It is the factor that connects the body and the mind, because it is connected on one side with the body and on the other side with the mind. It is the connecting link between the body and the mind. The body and the mind have no direct connection. They are connected through Prana only.

— Swami Chidananda Saraswati

Yoga primarily works with the energy in the body through the science of pranayama or energy-control. Prana also means ‘breath.’ Yoga teaches how to still the mind through breath-control and attain higher states of awareness. The higher teachings of yoga take one beyond techniques and show the yogi or yoga practitioner how to direct his concentration in such a way as not only to harmonize human with divine consciousness, but to merge his consciousness in the Infinite.

— Paramahansa Yogananda

 Hatha

and Raja Yoga Varieties

Some scholars distinguish between hatha and raja yoga varieties of pranayama, with the former variety usually prescribed for the beginner. According to Taimni, hatha yogic pranayama involves manipulation of pranic currents through breath regulation for bringing about the control of chitta-vrittis and changes in consciousness, whereas raja yogic pranayama involves the control of chitta-vrittis by consciousness directly through the will of the mind. Students qualified to practice pranayama are therefore always initiated first in the techniques of hatha pranayama.

Bhagavad Gītā

Pranayama is mentioned in verse 4.29 of the Bhagavad Gītā.
According to Bhagavad-Gītā As It Is, "prāṇāyāma" is translated to "trance induced by stopping all breathing", also being made from the two separate Sanskrit words, "prāṇa" and "āyāma".
Pranayama is the fourth 'limb' of the eight limbs of Ashtanga Yoga mentioned in verse 2.29 in the Yoga Sutras of Patanjali. Patanjali discusses his specific approach to pranayama in verses 2.49 through 2.51, and devotes verses 2.52 and 2.53 to explaining the benefits of the practice. Patanjali does not fully elucidate the nature of prana, and the theory and practice of pranayama seem to have undergone significant development after him. He presents pranayama as essentially an exercise that is preliminary to concentration, as do the earlier Buddhist texts.
Many yoga teachers advise that pranayama should be part of an overall practice that includes the other limbs of Patanjali's Raja Yoga teachings, especially Yama, Niyama, and Asana.

Medical

Several researchers have reported that pranayama techniques are beneficial in treating a range of stress-related disorders, improving autonomic functions, relieving symptoms of asthma (though a different study did not find any improvement and reducing signs of oxidative stress. Practitioners report that the practice of pranayama develops a steady mind, strong will-power, and sound judgement, and also claim that sustained pranayama practice extends life and enhances perception.

Cautions

Many yoga teachers recommend that pranayama techniques be practiced with care, and that advanced pranayama techniques should be practiced under the guidance of a teacher. For example, people with high blood pressure must perform it cautiously or may even have to avoid it. These cautions are also made in traditional Hindu literature. Pregnant women may have to forgo pranayama.