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Breathing in, or inhaling, is usually an active movement, with the contraction of the diaphragm muscles needed. At rest, breathing out, or exhaling, is normally a passive process powered by the elastic recoil of the chest, similar to a deflating balloon. The following organs are used in respiration: mouth, nose, gullet, windpipe, lungs, diaphragm.

Gas exchange

Breathing is only part of the process of delivering oxygen to where it is needed in the body. The process of gas exchange occurs in the alveoli by passive diffusion of gases between the alveolar gas and the blood passing by in the lung capillaries. Once in the blood the heart powers the flow of dissolved gases around the body in the circulation.


Control of breathing


Conscious control

Conscious attention to breathing is common in many forms of meditation, specifically anapana and other forms of yoga. In swimming, cardio fitness, speech or vocal training, one learns to discipline one's breathing, initially consciously but later sub-consciously, for purposes other than life support.

Unconscious control


This automatic control of respiration can be impaired in premature babies, or by drugs or disease.





It is not possible for a healthy person to voluntarily stop breathing indefinitely. If we do not inhale, the level of carbon dioxide builds up in our blood, and we experience overwhelming air hunger. This irrepressible reflex is not surprising given that without breathing, the body's internal oxygen levels drop dangerously low within minutes, leading to permanent brain damage followed eventually by death. However, there have been instances where people have survived for as long as two hours without air; this is only possible when submerged in cold water, as this triggers the mammalian diving reflex.[1]

If a healthy person were to voluntarily stop breathing (i.e. hold his or her breath) for a long enough amount of time, he or she would lose consciousness, and the body would resume breathing on its own. Because of this one cannot suffocate oneself with this method, unless one's breathing was also restricted by something else (e.g. water, see drowning)

Hyperventilating causes a drop in CO2 below normal levels, lowering blood acidity to trick the brain into thinking it has more oxygen than is actually present. Hyperventilating can cause your blood oxygen levels to go to dangerous levels.

Relationship to death

Breath is sometimes used as a metaphor for life itself, and often "last breath" is the most obvious sign that death has occurred. The association between the end of life and breathing is not absolute, however. As modern treatment can now take over the process of breathing by mechanical ventilation, or cardiopulmonary resuscitation (CPR), breathing can be restarted if it stops. Because of this, modern deaths are now better defined in terms of brain dysfunction.

Composition of air

The air we inhale is roughly 78% nitrogen, 21% oxygen, 0.96% argon and 0.04% carbon dioxide, helium, water, and other gases. (% by volume)

The permanent gases in air we exhale are roughly 78% nitrogen, 15% to 18% oxygen, 4% to 5% carbon dioxide and 0.96% argon (% by volume). Additionally vapors and trace gases are present: 5% water vapor, several parts per million (ppm) of hydrogen and carbon monoxide, 1 part per million (ppm) of ammonia and less than 1 ppm of acetone, methanol, ethanol and other volatile organic compounds.

Not all of the oxygen breathed in is replaced by carbon dioxide; around 15% to 18% of what we breathe out is still oxygen. The exact amount of exhaled oxygen and carbon dioxide varies according to the fitness, energy expenditure and diet of that particular person. Also our reliance on this relatively small amount of oxygen can cause overactivity or euphoria in pure or oxygen rich environments.

Cultural significance

In Tai Chi Chuan, aerobic training is combined with breathing to exercise the diaphram muscles, and to train effective posture, which both make better use of the body's energy. In music, breath is used to play wind instruments and many aerophones. Laughter, physically, is simply repeated sharp breaths. Hiccups and yawns are other breath-related phenomena.

Ancients commonly linked the breath to a life force. The Hebrew Bible refers to God breathing the breath of life into clay to make Adam a living soul (nephesh, roughly "breather"). It also refers to the breath as returning to God when a mortal dies. The terms "spirit," "qi," and "psyche"[2] are related to the concept of breath.


  2. ^ [1]
  • Parkes M (2006). "Breath-holding and its breakpoint.". Exp Physiol 91 (1): 1-15. PMID 16272264. Full text

See also

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Breath". A list of authors is available in Wikipedia.