The practice of breath control has its roots in Eastern culture, among the Hindu yogis and Chinese sages. They utilized these breathing techniques to regulate emotions, to heal physiological imbalances, to increase martial prowess, and for spiritual enlightenment.
From a physiological perspective, respiration is the exchange of oxygen and carbon dioxide between the air and the blood in the lungs. Oxygen is injected into the red blood cells while carbon dioxide is ejected from them into the air. The oxygenated blood then flows back to the heart via the pulmonary veins. The heart then pumps the blood throughout the systemic arteries to deliver oxygen throughout the body.
Traditional Chinese Medicine views breath as a modulating factor in the development and usage of qi (energy). The lungs take in external qi from air and combines it with "Gu Qi" or food energy. Gu qi, is the energy derived from food in its early stage of transformation within the digestive system. It is not considered to be fully transformed into a energy rich source. It must intermingle with the lung energy, which ultimately energizes the Gu qi to form into Zong qi. Furthermore, Zong qi needs support from abundant Kidney energy, or "Yuan qi". Yuan qi is your prenatal energy, past on to you by your parents. This energy comes in a fixed quantity, but can be nourished by a healthy lifestyle (eg. diet). It is also the foundation of yin and yang energies in the body. It is the Yuan qi which facilitates the transformation of Gu qi into blood, motivating functional activity of the internal organs. When the Yuan qi flows upward via the channels (eg. san jiao, aka. triple burner) it aids in the formation of Zong qi, which in turn nourishes the heart and lungs. Thereby promoting respiration and circulation of oxygenated blood. If the Zong qi is weak, the extremities will be weak and cold, the voice will be low and the immune system susceptible to invasion by viruses and bacteria. Zong qi, with the help of Yuan qi, is refined into what is called Zhen qi or normal qi. This energy is further divided into two forms called ying qi and wei qi.
Ying Qi nourishes the internal organs and the whole body. It is closely related to blood, and flows with blood in the vessels, as well as in the channels. TCM physiology, regards ying qi as a motivating force which helps to transform food essence into blood. Wei qi on the other hand, circulates outside of the vessels, between the skin and muscles. Its function is to protect the body from attack (eg. infections etc.), warms and keeps the skin moist, and controls the opening and closing of the pores, in regulation of perspiration.
The practice of enhancing breath control, through qigong, taiji (tai chi), meditation, or yoga, plays a major role in the creation of different types of internal energy, in the optimal functioning of circulation, digestion and overall organ function. Along with proper body mechanics, one can inhale and exhale with less effort, and also increase total volume of air taken in. Structural and functional changes such as improved lung elasticity, more efficient gas exchange, improved nervous system sensitivity, stress regulation, and overall body awareness will develop with consistent practice. In fact, greater breathing efficiency is associated with a reduced risk of heart, respiratory, joint diseases and also a reduced risk of cognitive decline.
"When the breath wanders the mind also is unsteady. But when the breath is calmed the mind too will be still, and the yogi achieves long life. Therefore, one should learn to control the breath." ~Svatmarama, Hatha Yoga Pradipika