This article was originally published in Positive Health issue 49 – February 2000

Did you know that you have, inside your body, a particular kind of umbrella? An umbrella you’ll never forget to take with you, or manage to lose, since it is your own flesh. From the first cry of birth to the very last breath, it opens and closes non-stop. It is made of muscles and tendons and is called the diaphragm.

Tissié, a doctor and gymnast, was the first, as far as I know, to make the analogy with an umbrella. The diaphragm, he suggested:
– is shaped like a dome;
– has serrated sides;
– is thin and impermeable;
– increases its tension by lowering its centre;
– and in closing, its periphery goes down while its centre goes up…
After reading that, you might well feel as if you have swallowed an umbrella!

The origin of the word diaphragm suggests a ‘fence’ or partition’. Indeed, the diaphragm marks the great divide between the upper and lower body. Above it, is the thorax and the world of ventilation; below, the abdomen and the world of digestion. The diaphragm is a muscular partition which behaves as a floor to the chest cavity and a ceiling to the abominal cavity.

Anatomically speaking, the diaphragm presents some interesting particularities. It is attached to the front part of the spine by two crura, or pillars. The right one is larger and longer than the left one. The centre of the diaphragm is made of two domes, the right one bigger than the left. In other words, the diaphragm is asymmetric.

The attachments of the psoas muscle overlap those of the iliacus and diaphragm. Like the three musketeers, these muscles are ‘one for all and all for one’. Together, they form what Mézières calls a Muscular Chain.

Dr Tissié summed up these connections with the letter K (known as ‘the K of Tissié’), where the upright represents the spine (viewed from the side); the upper diagonal, the diaphragm; and the lower one, the psoas. The centre of this ‘K’ is an important junction, at the crossroad of two physiological worlds, occupied by important elements of the nervous system. In this strategic region is the biggest network of sympathetic nerves: the solar plexus or so-called ‘abdominal brain’.

However, the diaphragm is an awkward umbrella as it is full of holes. There are three large and several smaller apertures known as the openings. The large ones are for the passage of the aorta, the oesophagus and the vena cava.

These tubes going through our umbrella muscle are a clue to some of the many functions performed by the diaphragm. Whereas normal umbrellas have only two roles – to protect us against rain or strong sun – the umbrella muscle has a number of functions. In fact, it participates in all the functions of the body. Consequently, it deserves to be called the King muscle, the most important of all the skeletal muscles.

The diaphragm is best known for the part it plays in breathing. In Man, an internal breathing system has been favoured, and accordingly the diaphragm is our main breathing muscle.

The mechanism of breathing triggered by the diaphragm has confused many great scientists of the past and still confuses many laypersons. If you are in this category, remember the umbrella: when you open it, the centre goes down and its canopy becomes tight; when you close it, the centre goes up, and the canopy becomes loose. It is the same with the diaphragm. It contracts during inspiration, lowering its centre and relaxes during expiration, allowing the centre to return to its initial position.

A muscle can only pull; it cannot push. How then can the diaphragm increase the three diameters of the ribcage? The solution to this puzzle lies in the fact that the diaphragm has the particularity of possessing a central tendon. When the diaphragm contracts, the central tendon goes down like a piston. This action increases the vertical diameter of the ribcage. But this downward movement is soon checked by the suspensory ligament of the diaphragm and by the abdominal organs. The now lowered central tendon has become static and acts as a fixed point from which the muscle fibres can lift the lower ribs and also the upper ribs via the breast bone. A really clever design!

As the level of the diaphragm is constantly changing due to its excursions during breathing, all of the attached organs have to follow its up and down movements. Life for these organs is spent in a lift: ground floor, second floor; ground floor, second floor… but they don’t mind at all. They actually need this down and up-lifting life and enjoy the constant exercise and massage. It is only when the excursion of the diaphragm is lessened that they start to complain.

As indicated above, breathing is not the only function of the diaphragm. It also participates in blood and lymphatic circulation, acting like a muscular pump; in phonation; in digestion; it has a postural role; it assists the heart; and finally it is behind all expulsive actions (giving birth, sneezing, coughing, crying, vomiting, urinating, and defecating). Truly a Jack of all trades.

Having so many duties to perform, it is no wonder that when the diaphragm is prevented from working normally, many things can go wrong. Disturb it and a trail of symptoms can follow, from asthma to varicose veins.

Following this brief study of the anatomy and physiology of the diaphragm, we will in the next issue, have a closer look at the pathology caused by its malfunctioning. In the meantime, remember that while an umbrella works only when it is open, the diaphragm works when it regularly opens and closes – so don’t be tempted to hold your breath!