OF THE INFLUENCE OF THE DEATH OF THE HEART OVER THAT OF THE LUNGS.
The lungs are the seat of two very different sorts of phenomena.
The first, which are entirely mechanical, are relative to the
rise and fall of the ribs and diaphragm, to the dilatation and
contraction of the air vessels, and to the entry and exit of the
air, which is the effect of these movements. The second, which are
purely chemical, may be referred to the different alterations,
which the air and blood experience.
These two sorts of phenomena have a mutual dependence on each
other. Without the mechanical, the chemical changes could not be
made; without the chemical changes, the blood would cease to become
an excitant to the brain, in consequence of which that organ would
no longer operate upon the diaphragm or intercostal muscles; the
muscles themselves would then become inactive, and the motions of
the thorax be annihilated. These phenomena, however, are put an end
to in a different manner by the death of the heart, accordingly as
it happens on one or the other side.
I. _In what manner are the actions of the lungs interrupted, when
the black-blooded heart ceases to act?_
The heart has certainly no influence over the mechanical functions
of the lungs, but it contributes essentially to produce the
chemical changes which are made there, by sending thither the
fluid which is destined to undergo a change. When its functions
then are interrupted as may happen from wounds or be occasioned by
ligature, the chemical changes which should be made in the blood,
are suddenly suppressed; though the air continue to enter into the
lungs, from the dilatation and contraction of the chest.
Meanwhile there arrives nothing at the red-blooded heart, or[68]
so little as to be insufficient for the production of the cerebral
movements. The functions of the brain are consequently suspended,
and of course the movements of the diaphragm and ribs.
II. _In what manner are the actions of the lungs interrupted, when
those of the red-blooded heart are suspended?_
Whenever from wound, ligature, or aneurism, the functions of the
red-blooded heart or aorta cease, the functions of the lungs are
terminated in the following order:
1st. There is no further impulse made upon the brain. 2dly, No
further movement of that organ.[69] 3dly, No further action
exercised upon the muscles. 4thly, No further contraction of the
intercostals or diaphragm. 5thly, The mechanical functions of the
lungs cease. 6thly, Their chemical functions cease.
In the former case, the chemical changes could not be made for want
of blood. Here they cannot be made for want of air. Such is the
difference in the death of the lungs, in consequence of that of the
heart, according as the latter is affected. But as the circulation
is very rapid, there cannot be but a very short interval between
the interruption of the chemical and the mechanical functions of
the lungs.
FOOTNOTES:
[68] After the obliteration of the ductus arteriosus, the left
ventricle receives no blood but what comes from the lungs; now, if
the motions of the thorax continue, it is red blood; at least so
long as the air is freely admitted into the bronchial tubes, and so
long as the composition of this fluid is not changed by the mixture
of foreign gases.
[69] These two modifications should, after what we have said, be
reduced to a single one, viz. want of excitement of the brain by
the arterial blood.