When it is necessary to create the material universes, Viṣṇu expands Himself as Mahā-Viṣṇu. Mahā-Viṣṇu lies down in the Causal Ocean and breathes all the universes from His nostrils. Thus from Mahā-Viṣṇu and the Causal Ocean spring all the universes, and all these universes, including ours, float in the Causal Ocean. In this regard there is the story of Vāmana, who, when He took three steps, stuck His foot through the covering of this universe. Water from the Causal Ocean flowed through the hole that His foot made, and it is said that that water became the river Ganges. Therefore the Ganges is accepted as the most sacred water of Viṣṇu and is worshiped by all Hindus, from the Himalayas down to the Bay of Bengal.
(Sri Caitanya Caritamrta------introduction).

Countless universes reside like seeds within the skin pores of Mahā-Viṣṇu, and when He exhales, they are all manifested. In the material world we have no experience of such a thing, but we do experience a perverted reflection in the phenomenon of perspiration. We cannot imagine, however, the duration of one breath of Mahā-Viṣṇu, for within one breathall the universes are created and annihilated. This is stated in the Brahma-saṁhitā. Lord Brahmā lives only for the duration of one breath, and according to our time scale 4,320,000,000 years constitute only twelve hours for Brahmā, and Brahmā lives one hundred of his years. Yet the whole life of Brahmā is contained within one breath of Mahā-Viṣṇu. Thus it is not possible for us to imagine the breathing power of Mahā-Viṣṇu, who is but a partial manifestation of Lord Nityānanda.
(Sri Caitanya Caritamrta------introduction).

The original quadruple forms—Kṛṣṇa, Baladeva, Pradyumna and Aniruddha—expand into another quadruple, which is present in the Vaikuṇṭha planets of the spiritual sky. Therefore the quadruple forms in the spiritual sky are the second manifestation of the original quadruple in Dvārakā. As explained above, Vāsudeva, Saṅkarṣaṇa, Pradyumna and Aniruddha are all changeless, transcendental plenary expansions of the Supreme Lord who have no relation to the material modes. The Saṅkarṣaṇa form in the second quadruple is not only a representation of Balarāma but also the original cause of the Causal Ocean, where Kāraṇodakaśāyī Viṣṇu lies asleep, breathing out the seeds of innumerable universes.
(Sri Caitanya Caritamrta-----1:5:41------purport).

Sometimes he would take his bath in the River Godāvarī. After taking his bath he would sit in a secluded place on the bank of the river, and by practicing the yoga exercises of prāṇāyāma, the usual breathing exercises, he would concentrate his mind. These breathing exercises are meant to mechanically fix the mind upon a particular subject. That is the result of the breathing exercises and also of the different sitting postures of yoga. Formerly, even quite ordinary persons used to know how to fix the mind upon the remembrance of the Lord, and so the brāhmaṇa was doing this. When he had fixed the form of the Lord in his mind, he began to imagine in his meditations that he was dressing the Lord very nicely in costly clothing, with ornaments, helmets and other paraphernalia.
(Nectar of Devotion).

The personified Vedas continued: “Dear Lord, it is imperative that the living entities be engaged in Kṛṣṇa consciousness, always rendering devotional service by such prescribed methods as hearing and chanting and executing Your orders. If a person is not engaged in Kṛṣṇa consciousness and devotional service, it is useless for him to exhibit the symptoms of life. Generally if a person is breathing he is accepted to be alive. But a person without Kṛṣṇa consciousness may be compared to a bellows in a blacksmith's shop. The big bellows is a bag of skin which exhales and inhales air, and a human being who simply lives within the bag of skin and bones without taking to Kṛṣṇa consciousness and loving devotional service is no better than the bellows. Similarly, a nondevotee's long duration of life is compared to the long existence of a tree, his voracious eating capacity is compared to the eating of dogs and hogs, and his enjoyment in sex life is compared to that of hogs and goats.”
(Krsna Book).

Still others, who are inclined to the process of breath restraint to remain in trance, practice by offering the movement of the outgoing breath into the incoming, and the incoming breath into the outgoing, and thus at last remain in trance, stopping all breathing. Others, curtailing the eating process, offer the outgoing breath into itself as a sacrifice.
This system of yoga for controlling the breathing process is called prāṇāyāma, and in the beginning it is practiced in the haṭha-yoga system through different sitting postures. All of these processes are recommended for controlling the senses and for advancement in spiritual realization. This practice involves controlling the airs within the body so as to reverse the directions of their passage. The apāna air goes downward, and the prāṇa air goes up.
(Bhagavad-Gita------4:29------translation and purport).

The prāṇāyāma-yogī practices breathing the opposite way until the currents are neutralized into pūraka. equilibrium.
(Bhagavad-Gita------4:29------purport).

Offering the exhaled breath into the inhaled breath is called recaka.
(Bhagavad-Gita------4:29------purport).

A person in the divine consciousness, although engaged in seeing, hearing, touching, smelling, eating, moving about, sleeping and breathing, always knows within himself that he actually does nothing at all. Because while speaking, evacuating, receiving, or opening or closing his eyes, he always knows that only the material senses are engaged with their objects and that he is aloof from them.
(Bhagavad-Gita------5:8-9------translation).

Shutting out all external sense objects, keeping the eyes and vision concentrated between the two eyebrows, suspending the inward and outward breaths within the nostrils, and thus controlling the mind, senses and intelligence, the transcendentalist aiming at liberation becomes free from desire, fear and anger. One who is always in this state is certainly liberated.
(Bhagavad-Gita------5:27-28------translation).

The breathing movement is restrained within the nostrils by neutralizing the up-moving and down-moving air within the body.
(Bhagavad-Gita------5:27-28------purport).

There are innumerable universes, with one Brahmā in each of them, and all of them are created and annihilated during the breathing time of the puruṣa. Therefore one can simply imagine how many millions of Manus there are during one breathof the puruṣa.
(Srimad Bhagavatam-----1:3:5------purport).

Even when the gross body is not acting when the living being is in sound sleep, we know that he is within the body by his breathing.
(Srimad Bhagavatam-----1:3:32------purport).

That the Personality of Godhead was not seen but only heard does not make any difference. The Personality of Godhead produced the four Vedas by His breathing, and He is seen and realized through the transcendental sound of the Vedas. Similarly, the Bhagavad-gītā is the sound representation of the Lord, and there is no difference in identity. The conclusion is that the Lord can be seen and heard by persistent chanting of the transcendental sound.
(Srimad Bhagavatam-----1:6:25------purport).

One who has controlled the sitting postures (the yogic āsanas) and the breathing process can turn the senses toward the Absolute Personality of Godhead and thus become immune to the contaminations of the modes of material nature, namely mundane goodness, passion and ignorance.
(Srimad Bhagavatam-----1:13:54------translation).

Lord Śrī Kṛṣṇa, the Supreme Personality of Godhead is ad infinitum, more powerful than the most powerful sun of our experience. Millions and billions of suns are created by Him and annihilated by Him within His one breathing period. In the material world the sun is considered to be the source of all productivity and material energy, and only due to the sun can we have the necessities of life. Therefore, during the personal presence of the Lord on the earth, all paraphernalia for our peace and prosperity, especially religion and knowledge, were in full display because of the Lord's presence, just as there is a full flood of light in the presence of the glowing sun.
(Srimad Bhagavatam-----1:14:2------purport).

The material color of the mind is changed when one washes it from contaminations of life-breathing and thereby frees it from the contamination of repeated births and deaths and situates it in pure spiritual life.
(Srimad Bhagavatam-----1:15:41------purport).

The perception of matter is transcended to still subtler states of the senses. The senses are transcended to the subtler mind, and then to breathing activities and gradually to intelligence. Beyond the intelligence, the living soul is realized by the mechanical activities of the yoga system, or practice of meditation restraining the senses, regulating thebreathing system and applying intelligence to rise to the transcendental position. This trance stops all material activities of the body.
(Srimad Bhagavatam-----1:18:26------purport).

Oṁkāra, or the praṇava, is the seed of transcendental realization, and it is composed of the three transcendental letters a-u-m. By its chanting by the mind, in conjunction with the breathing process, which is a transcendental but mechanical way of getting into trance, as devised by the experience of great mystics, one is able to bring the mind, which is materially absorbed, under control.
(Srimad Bhagavatam-----2:1:17------purport).

The first process of spiritualizing the mind by mechanical chanting of the praṇava (oṁkāra) and by control of the breathing system is technically called the mystic or yogic process of prāṇāyāma, or fully controlling the breathing air. The ultimate state of this prāṇāyāma system is to be fixed in trance, technically called samādhi.
(Srimad Bhagavatam-----2:1:18------purport).

The breathing air of life is produced of sky, air and water, and therefore open air, regular bath and ample space in which to live are favorable for healthy vitality.
(Srimad Bhagavatam-----2:10:31------purport).

The purpose of yogic performances is explained here. It is said that an experienced mystic attains full control of the senses and the mind by controlling the breathingprocess. Therefore, controlling the breathing process is not the ultimate aim of yoga. The real purpose of yogic performances is to control the mind and the senses.
(Srimad Bhagavatam-----3:15:7------purport).

The eight divisions of yoga performance are described as (1) control of the senses, (2) strict following of the rules and regulations, (3) practice of the different sitting postures, (4) control of the breath, (5) withdrawing the senses from sense objects, (6) concentration of the mind, (7) meditation and (8) self-realization. After self-realization there are eight further perfectional stages, which are called yoga-siddhis.
(Srimad Bhagavatam-----3:21:4------purport).

One must observe silence, acquire steadiness by practicing different yogic postures, control the breathing of the vital air, withdraw the senses from sense objects and thus concentrate the mind on the heart.
(Srimad Bhagavatam-----3:28:5------translation).

King Kulaśekhara, a great devotee of the Lord, prayed:
kṛṣṇa tvadīya-pada-paṅkaja-pañjarāntam
adyaiva me viśatu mānasa-rāja-haṁsaḥ
prāṇa-prayāṇa-samaye kapha-vāta-pittaiḥ
kaṇṭhāvarodhana-vidhau smaraṇaṁ kutas te
(MM 33)
"My Lord Kṛṣṇa, I pray that the swan of my mind may immediately sink down to the stems of the lotus feet of Your Lordship and be locked in their network; otherwise at the time of my final breath, when my throat is choked up with cough, how will it be possible to think of You?"
(Srimad Bhagavatam-----2:4:21------purport).