By Dr Kenneth Backhouse OBE
Breathing simply means pulling air into the lungs by expansion of their surrounding walls (inspiration) and then blowing it out again (expiration).
The air taken in contains about 20% oxygen and while that air is in the lungs some of the oxygen is removed by attachment to the haemoglobin in the blood, passing in the walls of the alveoli of the lungs, for carriage around the body. At the same time carbon dioxide that has been carried in the blood to the lungs is transferred to the contained air for removal at expiration. For most aspects of daily living the breathing process is controlled automatically but from time to time a more conscious control is needed to take over, as in aspects of dance, speech or singing.
The lungs together with the heart largely fill the chest. Each is somewhat conical in shape, that on the left being smaller than the right because the heart, lying between the lungs, is mainly to the left. Each lung consists of myriads of tiny elastic walled sacs (alveoli) rather like miniature balloons with the blood running through their very thin walls. The alveoli are linked to the outside world through the bronchial tubes to the central trachea and then via the larynx to the nose or mouth. The important thing to remember is that as the alveoli are tiny elastic balloons, the lungs containing them also act as highly elastic balloons. If you blow them up, as you would do in mouth-to-mouth (or nose) artificial respiration then the air is blown out again as from a blown up balloon.
The outer wall of the chest containing the lungs has a firm framework of the bony ribs. These are mounted at the back on the thoracic vertebrae; loop round and down like bucket handles to the front. Here the upper six are linked to the sternum (breast bone) by short costal cartilages and the next four by longer interlinked cartilages that give a more elastic edge to the lower rib margins. Under control of the intercostals and other muscles, the ribs can be raised from the back, increasing the depth of the chest from back to front. At the same time, rather as a bucket handle is lifted, so the curved ribs swing outwards and widen the chest. The result is an increase in volume of the chest and as the lungs follow the chest wall thoracic inspiration occurs. But the chest must also have a floor and this consists of a sheet of muscle that separates the chest cavity from the abdomen. This muscle (with a central tendon), the diaphragm, sweeps upwards, from the vertebrae at the back, the rib margins to the side and front and the sternum, forming a dome quite high into the chest when at rest. The dome is rather irregular in shape; quite low under the heart to the front but particularly high beneath the lungs so that when the muscle contracts the dome is lowered so increasing the height of the chest cavity and of the lungs. This aspect is known as diaphragmatic inspiration.
Inspiration requires a positive effort on behalf of the muscles controlling the chest wall to pull out the lungs and so open their alveoli, creating a negative pressure that pulls air in from the outside. Because of the elastic quality of the lungs, if those muscles relax the lungs also respond and, as a balloon, air is blown out. Quiet expiration is just simple relaxation of muscle and the elastic lungs do the work though for deeper and more forceful breathing muscular activity is added.
Although contraction of the diaphragm in inspiration increases the volume of the chest the volume of the abdomen below can not be reduced to compensate. The space can only be found by a compensatory relaxation of the abdominal wall and this occurs in that finely controlled region above the level of the umbilicus, leading to a bulging of the upper abdominal wall on inspiration. Although that aspect of breathing using the outer chest wall can simply be called thoracic respiration that involving the diaphragm is a complex and finely controlled balance between it and the abdominal muscles and strictly speaking should be abdomino-diaphragmatic respiration.
Before continuing it is worth mentioning the pleural cavity that worries many people. It is in fact not really a cavity at all. The lungs are surrounded by a serous membrane the pleura and a similar one lines the chest wall and the two are in contact to allow friction free movement of the delicate lung surface. The pleura secrete a lubricant, much as the synovial membrane in a joint, the very thin layer of lubricant is the only content of the so-called pleural cavity. (It is perhaps worth mentioning that if an opening is made in the chest wall, as may occur in an accident, because of the elastic nature of the lung, it will collapse as a deflating balloon and air from outside will fill what is now a real pleural space.)
For the simple processes of living, breathing is controlled automatically to provide what oxygen is required for the body and also to remove the carbon dioxide. It may seem a little odd but the mechanism is primarily linked to the level of carbon dioxide in the circulating blood and the need to remove this otherwise toxic gas. But in practice, as this is produced by the oxygen being used in tissue respiration in the body, under normal circumstances oxygen intake will balance the carbon dioxide produced and having to be discharged. As greater activity takes place more carbon dioxide is produced, rate and depth of breathing is increased to remove it and this also raises the oxygen intake. But breath is required for other purposes than metabolism, such as generation of the vibrations in the larynx for sound production. The brain takes conscious control of breathing for these purposes so long as the carbon dioxide level does not get too high and the oxygen level too low when the automatic control takes over with a 'gasp for air'.
In normal active day-to-day living both aspects of breathing, thoracic and diaphragmatic run together in roughly equal proportions of each, though varying from person to person. Obviously physical problems may induce variants, (later stages of pregnancy is obvious), nevertheless the proportion of diaphragmatic breathing in many people may be reduced to virtually nil for no apparent reason. This leaves only a proportion of respiratory potential (thoracic) available. For some reason it is more frequent in women and obviously if respiratory disease supervenes the problem becomes particularly important, as only a portion of respiratory movement is available.
Some years ago when teaching female students in a Physical Education College I commented on the problem. They told me, after examining themselves with their director, that I was talking nonsense. I reminded them that they were all physically active people and suggested that they looked to the ladies in a less physical department. Their views changed and as a result they set out to assess the problem when on school practice. They reported that before puberty girls showed full diaphragmatic breathing as the boys. After puberty the physically active girls continued to do so but many of the less active girls completely changed to primarily thoracic respiration. Why this should be is strange - especially to a male - as it was to my female students but once established it is difficult to break the routine and induce diaphragmatic breathing. It can be a problem in those activities where diaphragmatic breathing is important.
Breathing for dance or song
Diaphragmatic breathing is particularly important for trained singers and other users of voice as well as wind instrumentalists. All these people require a very finely controlled exhalation to induce fine vocal vibrations at the larynx or control of the wind to their instrument. The chest does play an important part in resonance for singers but the finely controlled flow of air needed for the high quality production of voice is induced by the elegantly controlled contraction of the upper abdominal muscles with a balanced relaxation of the diaphragm. So important is this in practice that 80% or even more of breathing may be diaphragmatic.
For those dancers who also sing a complete change of breathing pattern is required, particularly as the quite marked upper abdominal movement required for singing would be less attractive in the usually more exposed dancer’s body. Dance requires good respiratory efficiency with elegance and for this a balance between thoracic and diaphragmatic breathing is important. If you ask the average person to take a deep breath, as for exercise, this usually includes a general lift and expansion of the chest wall. For dance however much of the control of the arms comes from the upper chest and so this must remain free. With the elegant extension of the spine, asked for in dance, this reduces the thoracic curve to some extent and that in turn creates some lift in the rib cage while the dancer should focus on expansion of the lower chest in inspiration. This in turn allows a moderate controlled lowering of the diaphragm while the upper abdominal wall simply appears to flow with the chest but without the bulging seen in singing. In any case, in dance, the focus of the upper abdominal muscles is required for the elegant control of the upper trunk through to port de bras.
But just as control of breathing is important to give quality to voice, so is it used to give colour to dance. At a basic level inspiration plays its part in opening and rising movements and expiration in closing and lowering ones. A different aspect of breath control is taking a deep breath and holding it under pressure to give vital control and strength to the lumbar spine in lifting, so important in pas de deux.