Picture - Cosmic Polymath

NEW VIEW OF THE MECHANISM OF RESPIRATION 279
That the movements of respiration are due to vital action and very little to elasticity admits of direct proof.
They can for short intervals be brought under the influence of the will, in which case inspiration and expiration alike
are completely under control—that is, the air is deliberately drawn into the chest and deliberately expelled. In
inspiration it is not a case of air entering the chest by atmospheric pressure. On the contrary, the air is sucked
in. In expiration it is not a case of mere elasticity and mechanical recoil, as happens in an elastic bag discharging
itself independently. The air is deliberately forced out of the chest by muscular effort. In the production of
voice it is forced out in very varying quantity, a state of matters which could not possibly be produced by any form
of elastic recoil. The mechanism for the production of voice is described under " Phonograph," § 242. There is
fundamentally no difference as regards vitality between the inspiratory and expiratory acts. The mechanism by
which they are produced is situated partly in the thorax, partly in the abdomen, and partly in the diaphragm.
In order to account for the truly rhythmic character of the chest movements during respiration it is necessary
to discard the elasticity hypothesis, according to which the chest is opened by muscles while it is closed mechanically
by the elastic properties of the ribs, sternum, and other structures. It is necessary to substitute for the latter a
system of muscles which shall close the chest, in a manner not unlike that by which it is opened. In other words
it is necessary to provide co-ordinating muscles to those of the chest. These muscles are found in the walls of the
abdomen, and are as effective in closing the chest as the muscles of the thorax are in opening it. The recti abdominis
take a principal share in closing the chest.
In the respiratory movements the muscles of the chest and abdomen co-operate, and in the most natural
manner. The muscles of the chest elevate the ribs, those of the abdomen (the transversalis abdominis excepted)
depress them. Both sets of muscles act directly and at first hand on the ribs. When the ribs are drawn upwards
when the
and outwards, as in inspiration, by the shortening of the chest muscles, the abdominal muscles elongate :
ribs are drawn downwards and inwards, as in expiration, by the shortening of the abdominal muscles, the thoracic
muscles elongate.
The diaphragm closes or shortens in all its diameters and arches upwards during expiration. It has its own
inherent movements, but it is a co-ordinated muscle, and acts in conjunction with the muscles of the chest and
abdomen. It exerts a double power, namely, the power of shortening and closing by centripetal movements, and that
of dilating and opening by centrifugal movements. In inspiration the diaphragm by its descent and by its becoming
flatter compresses and pushes the viscera (especially the stomach and liver) lower into the abdomen. This accounts
for the bulging of the abdomen when the chest is expanded.
In expiration the diaphragm by its ascent and by its becoming more arched compresses and presses up the
thoracic contents. In the latter movement, the diaphragm receives powerful assistance from the shortening or
closing of the transversalis abdominis, which acting on the abdominal contents as a whole presses the liver and
stomach into the concavity of the diaphragm, and so aids and assists its movements. The diaphragm dilates and
elongates or opens when the transversalis abdominis, and abdominal muscles generally, shorten or close, and vice
vend. The diaphragm shortens or closes when the muscles of the chest elongate or open, and the converse. In
this way a powerful muscular rhythmic apparatus is provided, sufficient to account for all the respiratory and
abdominal movements. The rhythms are mtiscular throughout, and the ribs and other bones and structures and
the elasticity thereof play quite a subordinate part.
The muscles of the thorax, abdomen, and diaphragm form part of a complex rhythmic system which has for
its object the intake and output of air, fluids, and solids. The movements are fundamental, vital, co-ordinated
movements, which are absolutely necessary to the life and well-being of the individual. Life cannot be maintained
without air, fluids, and soHds, and the apparatus dealing with these must be of the most perfect kind ; it must work
day and night, apart from effort on our part. Of all the vital movements those connected with respiration are in
some senses the most important. The exclusion of air from the lungs for more than a few minutes inevitably results
in death. Looking at the early connection between the lungs and alimentary canal, and the common rhythmic
function discharged by them, it will occasion no surprise if I say, and say deliberately, that not only the muscles of
the thorax but ako those of the abdomen, as well as those of the diaphragm, are necessary to the due discharge of the
functions of respiration.
One has only to study the general disposition and the origins and insertions of the muscles of the thorax, the
abdomen, and the diaphragm to be convinced of this. Nearly all these muscles are attached in some way to the
ribs, costal cartilages, and sternum ; those which are to pull the ribs up being attached for the most part to fixed
points above the ribs ;
those which are to pull the ribs down being attached to fixed points below the ribs.
The respiratory movements proper— and in these I include the rhythmic movements occurring in the nostrils,
the glottis, the lungs, the diaphragm, chest, abdomen, and other parts of the body—are at once involved and
difficult.