Suffocation may be defined, the destruction of life by the suspension of
the function of respiration, occasioned by external violence. Unless we
add “_by external violence_” we shall perceive that the definition would
be far too comprehensive; and the term _Suffocation_ would be made to
embrace a much wider range of subjects than its popular acceptation
would allow. If the physiological views be correct which we have adopted
and explained in the foregoing section, “On the causes and phenomena of
sudden death,” we should be compelled, without such a protecting
adjunct, to include under the history of Suffocation, not only the
phenomena of Drowning, Strangling, Hanging, Smothering, and noxious
inhalation, but even those of Apoplexy, fatal Intoxication, and various
diseases of the brain and spinal marrow, together with the effects of a
great proportion of Poisons; for by such agents death is undoubtedly
occasioned through the failure of the respiratory functions.
In Death from Suffocation the heart continues to pulsate for several
minutes after the breathing has entirely ceased, in consequence of which
the blood which passes through the pulmonary vessels no longer receives
the influence of oxygen, and therefore _black_ blood circulates; the
brain, it would appear, soon feels the want of the florid arterial
stream, by which alone its energies can be maintained. _Bichat_ has
shewn that when dark coloured blood is injected into the vessels of the
brain, by means of a syringe connected with the carotid artery, the
functions of the brain become immediately disturbed, and, in a short
time, entirely cease; the effect is precisely similar, whether the dark
coloured blood be transmitted to the brain by the syringe of the
experimentalist, or by the heart itself. It is not until after the full
effects of the suspended respiration are thus produced on the brain,
that the motions of the heart become enfeebled, and that the ventricles
contract less powerfully, and at longer intervals; at length, the action
of the heart is altogether arrested, and if the thorax be examined at
the instant that the circulation has ceased, nothing is observed, except
a slight tremulous motion of the auricles; the cavities of the left side
are much contracted, and contain only a small quantity of blood, while
the right auricle and ventricle, and the large vessels communicating
with them, are distended to an unusual size. This state of the heart, it
will be observed, is very different from that which we have described as
constantly occurring after _Syncope_. In the contemplation of these
phœnomena, a question very naturally suggests itself in regard to the
probable interval which elapses between the cessation of respiration,
and the consequent failure of the heart’s action; in other words, it may
be asked, how long can the heart support its contractions without the
aid of respiration? It would appear that this interval not only varies
in duration in different animals, but even in the same animal under
different circumstances, such as that of age,[25] capacity of the
thorax, quantity of air in the lungs, state of the stomach, and general
vigour of the animal; but in man, under the most favourable
circumstances, it is extremely doubtful whether the heart ever continues
to pulsate for so long a period as five minutes[26] after the lungs have
ceased to perform their office; and it is very questionable whether, in
most instances, the interval is not considerably shorter than this.