Breathing transports oxygen into the body and carbon
dioxide out of the body. Aerobic organisms
require oxygen to create energy via respiration, in the form of energy-rich
molecules such as glucose. The medical term for normal relaxed
breathing is eupnoea. Organisms breathe to avoid death from asphyxiation.
Mechanics
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 gasses between the alveolar gas and
the blood passing by in the lung capillaries. Once in the
blood the heart powers the flow of dissolved gasses around the body
in the circulation.
As well as carbon dioxide, breathing also results in loss of water from the body. Exhaled air has a relative
humidity of 100% because of water diffusing across the moist surface of breathing passages and alveoli.
Control of breathing
Breathing is one of the few bodily functions which, within limits, can be controlled both consciously and unconsciously.
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 other purposes than life support.
Unconsciously, breathing is controlled by specialized centers in the brainstem, which
automatically regulate the rate and depth of breathing depending on the body’s needs at any time. When carbon dioxide levels
increase in the blood, it reacts with the water in blood, producing carbonic acid. The drop in the blood's pH will then cause the medulla oblongata signalling center in the brain to
send nerve impulses to the diaphragm and the intercostal muscles, increasing the rate of breathing. While exercising, the level of carbon dioxide
in the blood increases due to increased cellular respiration by the
muscles. This stimulates chemoreceptors in the carotid and aortic bodies in the blood system to
send nerve impulses to the inspiration centre. The inspiration centre sends impulses to the diaphragm and intercostal muscles
through the phrenic and thoracic nerves. The diaphragm and intercostal muscles contract at a higher rate.
During rest, the level of carbon dioxide is lower, so breathing rate is lower. This ensures an appropriate amount of oxygen is
delivered to the muscles and other organs. It is important to reiterate that it is the buildup of carbon dioxide making the blood
acidic that elicits the desperation for a breath much more than lack of oxygen. 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. This results
that one cannot suffocate themself 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 disfunction.
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). Additionaly vapours and trace gases are present: 5% water vapour, 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 16% 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 instrument 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.
References
- ^ Ramey CA, Ramey DN, Hayward JS. Dive response of children inrelation to
cold-water near drowning. J Appl Physiol 2001;62(2):665-8.Source: Diana Hacker (Boston: Bedford/St. Martin’s, 2002).Adapted from
Victoria E. McMillan (Boston: Bedford/St. Martin’s, 2001). See it cited here
- ^ [1]
- Parkes M (2006). "Breath-holding and its breakpoint.". Exp Physiol 91 (1):
1-15. PMID 16272264.
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See also
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