In normal respiration the air is taken in through the nostrils without any special effort, sound or exaggerated movement of the nose or chest. In short, it is done unconsciously. We are not even aware of air traveling through our nostrils, down the nasal and oral parts of the pharynx, of its reaching the larynx and then the trachea and the lungs. In general, most of us are unaware of how the breathing process works.

We will take a look at: Stages in breathing, Kinds of breathing, Organs of breathing, Processes in breathing and  Ways of controlling breathing.


Stages in Breathing

Each single act of normal, unmodified breathing consists of four distinguishable stages:

"Breathing In", Inhaling Or Inspiration

The Pause, Short Or Long, Between Inhalation And Exhalation. We Will Call This Retentive Pause And Readjustment Phase

"Breathing Out," Exhaling Or Expiration.

The Pause, Long Or Short, Between Exhalation And Inhalation. We Will Call This Stage Extensive Pause And Its Readjustment Phase.

The two "resting" stages may or may not be very restful since the whole respiratory system, including its muscular and nervous mechanisms, undergoes a reversal of direction and multitudes of minute adaptations take place whenever each such reversal occurs.

All four are entailed in a complete act of respiration.

Kinds of Breathing

We can distinguish at least 12 different kinds of breathing. These are given below.

Although yogic treatises do not normally do so, Dechanet, author of ‘Christian Yoga,’ identifies two ways of breathing: "One for men, the other for women". He says that a woman's breathing rhythm is more rapid than a man's and that her upper chest expands first, whereas a man's breathing rhythm is slower and his abdominal expansion comes first. Although, doubtless, physiological differences in men and women do affect their breathing, I suspect that the world over, women breathe more placidly than men and that the differences which Dechanet notices may be related partly to size of body rather than sex. Smaller bodies may be expected to have a shorter, and perhaps more rapid, rhythm stroke than larger bodies. The fact that women live longer than men, on the average, may be due to many factors; but a study of breathing habits in men and women, especially in the older ages, may prove enlightening. However, distinctions of sex do not normally play a significant role in discussions of breathing.

Noisy versus quiet breathing is a distinction which has its significance in other conditions. Snoring may indicate deep slumber; wheezing, asthma and panting, shortness of breath; and other noises, clogging of nasal passages. But traditional yogic exercises do deliberately seek to control the loudness or softness of breathing and, in addition to giving directions for increasing loudness and softness, often combine both increases and decreases in subtle ways, synthesizing them in larger, more encompassing experiences, as in mantric chanting of the sacred symbol om.

Fast And Slow Breathing

Regular And Irregular Breathing

Jerky And Smooth Breathing

Deep And Shallow Breathing

Forced And Effortless Breathing

Voluntary And Involuntary Breathing

Mouth And Nose Breathing

The distinction between "high," "middle," and "low" breathing, where most of the expansion is in the top, middle or bottom parts of the chest and lungs, and the joining of all three in "complete yogic breathing."

The distinction between the mere passage of air in and out of lungs (with related physiological and mental effects) versus experiencing breathing as an affair of the whole body, the whole self, even of the whole universe as explored in pranayama.

The distinction between nervous and relaxed, vs. anxious and peaceful, breathing.
As we can see from the above classification of various breathing types, the process of breathing is very complex.

Organs of Breathing

Our respiratory system consists of nose and mouth, pharynx and larynx, trachea and bronchi, lungs and thorax.

Nose And Mouth

The nose consists of an outer shape and skin (which often receives more attention), and two air passages (nostrils).

Your nostrils differ in size and shape from those of other people. Most people breathe primarily through one nostril more than another. Whether relatively long or short, large or small, straight or crooked, nostrils vary in circumference and contour throughout their length. The bottom or floor surfaces of the nostrils tend to be more horizontal and the top or roof surfaces have been shaped more like an arch. A bony and cartilaginous septum separates your two nostrils.

The several nasal sinuses, including the better-known frontal sinuses in the forehead above the eyes and the maxillary sinuses on each side of the nose, play various roles in breathing, thinking, illness and in yoga. Most of us realize their existence when they become infected, as with colds, hay fever, or noxious gases or dusts, resulting in headaches. Some sinuses appear to perform an important function in cooling the brain. Nervous activity uses energy which seems to generate heat that needs to be conducted away. Thus, somewhat like the radiator of an automobile, the sinuses may serve as a cooling system for the brain, which supplements the circulatory system wherein the blood serves as a coolant. We seem to be able to think better when we have a "clearer head" resulting from well-ventilated sinuses. Deep breathing and posture exercises not only increase oxygenation through the lungs and circulation of the blood within the brain, but also tend to enlarge and clear the sinus cavities for freer air circulation.

The skin lining the nostrils consists primarily of membranes which do not dry out easily in the presence of moving air. They are kept moist by secretions called mucus which sometimes dries and hardens into a cake which must be expelled. Hairs embedded in such membranes, especially near the outer opening, often grow into sieve-like mats which catch and repel small objects, insects and dust. Olfactory end-organs are embedded in these membranes and some areas have a thick, spongy tissue which expands, so much sometimes-especially when irritated by infections or allergies-that it closes the nostril completely. Although yogic exercises may be insufficient by themselves to relieve clogged nasal conditions, they may help considerably.

The mouth, too, is an important air passage-especially when we need more air than can be forced through the nostrils, as when we gasp for air or pant or puff, and when the nostrils are closed by swollen membranes or mucous discharge. Membranes lining the mouth and tongue seem to dry up from air movements more rapidly than nasal membranes though saliva aids in maintaining moistness. The oral passage may be closed by the lips, by the tongue pressed against the teeth or roof of the mouth, and sometimes with the aid of the soft palate. Directions for opening and closure, partial or complete, of the mouth constitute parts of some directions for traditional yogic exercises.

Pharynx And Larynx

The pharynx is the opening behind the nasal cavities and mouth. It is bounded by the root of the tongue and is lined with tissues called tonsils which may become enlarged partially obstructing the passage of food and air. Two Eustachian tubes, which permit adjustment of atmospheric pressure in your middle ears, open from the sides of the pharynx. The pharynx ends in the esophagus or tube leading to the stomach and the larynx or "voice box," which contains the vocal cords and glottis and muscles needed for producing sounds. A cartilaginous epiglottis at the top of the larynx aids in closing it tightly so that solid and liquid foods will not be permitted to enter it during swallowing. Respiration is interrupted during swallowing. Yogins sometimes deliberately hold the epiglottis aperture closed to force holding air in or out of the lungs in certain exercises.

Trachea And Bronchi

The trachea or "windpipe" is a tube kept open against pressures because its walls consist in part of cartilaginous rings, or semi-rings. It is lined with a mucous membrane containing hair-like cells which beat upward toward the nose and mouth and move mucus and the entangled dust particles in that direction. It ends by dividing into two other tubes called bronchi which in turn branch again and again until they terminate in bronchioles, thin-walled tubes which lead to tiny air sacs with their small dilations called alveoli where most of the gas exchange takes place. The mucosa of the trachea and bronchi contain ciliated epithelium.

Lungs And Thorax

Each of the two lungs consists of

Bunches of bronchioles and alveoli,

Blood vessels and capillaries, and

Elastic tissue.


These are arranged in lobes and are surrounded by a membrane that secretes a lubricating fluid. The lungs, together with the heart, occupy most of the thoracic or chest cavity, bounded on the sides by the ribs and on the bottom by the diaphragm. The diaphragm separates the chest cavity from the abdomen containing most of the digestive system.

The pleural sacs and the inner lining of the thorax are airtight. Since the only opening from the outside is the trachea, air may be forced in or out of the lungs by enlarging or compressing the thoracic area. Three sets of muscles are primarily responsible for changing the size of the thorax. These are:


Those acting on the ribs,

Those acting between the ribs and

Those acting on the diaphragm


Other muscles of the body, such as those in the arms, legs and back, may twist the body so as to distort its usual shape and exert pressures that squeeze or expand the chest cavity. A blow on the abdomen, wearing tight clothes, a full stomach or intestinal gas may also provide temporary pressures on the thorax thus affecting the breathing process.

Processes in Breathing

Respiration

An average adult at rest inhales and exhales about sixteen times per minute. Each time, half a liter (about a pint) of air is drawn in and expelled. At the end of a normal expiration, one may force out an additional liter and a half of air, leaving about an additional liter in the lungs which cannot be forced out. Also, after normal inspiration, one may inspire an additional one and a half liters. So it is possible to increase the amount of air inspired and expired during each breath from half a liter to three and a half liters.

Not all of the air breathed can be used by the body because some must remain to fill the nose or mouth, sinuses, larynx, trachea, bronchi and their larger branches. This is the "dead air" in contrast with "alveolar air" which participates in gas exchange. The shallower the breathing, the larger becomes the percentage of dead air in each breath. But also, in shallow breathing, more impurities are retained.

Most breathing exercises in yoga have the effect of increasing both the amount and percentage of air which enters actively into the purifying gaseous exchange processes.

The air inhaled normally consists of about 79% nitrogen, about 20% to 21% oxygen, about 0.04% carbon dioxide, with traces of other gases and water vapor. Exhaled air often consists of about 79% nitrogen, about 16% oxygen, about 4% carbon dioxide, with traces of other gases and water vapor. Since the nitrogen content remains approximately the same the most significant change during the breathing process is an exchange of about 4% oxygen for about 4% carbon dioxide.

Oxygenation

When the percentage of oxygen exchanged for carbon dioxide remains the same, the total amount of oxygen and carbon dioxide exchanged per minute tends to increase as a greater air volume is breathed. One may, by strenuous exercise, increase the volume of ventilation to ten times the resting level. Or one may deliberately force increased ventilation without exercise. When muscular exercise increases, the body needs more oxygen. When ventilation is forced intentionally, some increase in oxygen content and decrease in carbon dioxide content of the alveoli and blood may be expected. Part of the aim of both deep breathing exercises and posture movements and rests is to "purify" (increase the ratio of oxygen to carbon dioxide) the blood and the various parts of the body through which blood circulates.

The interchange of oxygen and carbon dioxide is possible because of the structure of the cells joining the alveoli and the capillaries and the laws and processes of gas exchange. The movement of carbon dioxide from the blood to the alveoli takes place by diffusion. In diffusion, the carbon dioxide moves from the rich side to the lean side. When the blood contains more carbon dioxide than the air, the carbon dioxide will diffuse from the blood to the air. If, on the other hand, the air is rich in carbon dioxide, the diffusion of carbon dioxide from the blood to the air is inhibited. In extreme cases the carbon dioxide may even diffuse or flow from the air into the blood. Thus our breathing habits are very important.

Regulation

A group of nerve cells in the medulla, the respiratory center of the brain, controls the contractions of muscles used in breathing. Inspiration takes place when the nerve cells of this group send impulses through motor nerves to respiratory muscles. When something, we do not know what, prevents these cells from sending impulses, inspiration ceases and expiration occurs. Apparently we do not use muscular energy and force to expel air but merely stop inhaling; then exhaling takes place automatically, without muscular effort. Since all respiratory muscles contract in a harmonious way, some organizing process in the brain marvelously coordinates their movements. Apparently the respiratory center cells function much like the pacemaker tissue of the heart, since they seem to induce rhythmical patterns of respiration without outside help, even though they are sensitive to various influences which modify their action.

In addition to the involuntary regulation and regularization of breathing patterns, many involuntary reflexes also exist, such as those noticeable in choking, sneezing, coughing, and swallowing. It is almost impossible to breathe while swallowing food. Other reflexes may be noted, such as sudden holding of breath when you sniff ammonia and similar chemicals. If your air supply has been cut off, you automatically gasp for breath. Emotional excitement, fear, anger, enthusiasm all stimulate breathing, as may sudden increase in either heat or cold.

There are voluntary control of breathing. For example, you can deliberately take a deeper breath or stop breathing momentarily. Such direct control may be supplemented by indirect intentional control, as when we dance or kiss or drink or smoke or sing. We may deliberately run for such a distance that we get our "second wind," after which we breathe more easily even though exercising strenuously.

Part of the significance of distinguishing between voluntary and involuntary control of breathing is that yogic exercises aim first at changing unhealthy involuntary patterns voluntarily and then at an establishment of more healthy patterns. Whereas nervous tension produces some inhibiting influence upon deep, regular breathing patterns, deliberate effort to counteract these influences in such a way that our more completely spontaneous and uninhibited rhythmic patterns become restored as needed.