is congestion of the brain or spinal cord. This congestion may be
pretty evenly distributed or it may vary in intensity in different
localities. This is especially true as regards the cord. It affects
both the meninges and the substance of the brain or cord. In most cases
there is more or less of serous effusion into the arachnoid. The
tissues of the scalp and those surrounding the spinal column are
sometimes engorged.
When sufficient time elapses before death the brain may be softened in
spots. This is probably due to the occlusion of vessels by coagula
formed during the primary congestion.
Congestions also occur in other localities, and especially in the solid
abdominal viscera. The liver and spleen have been found engorged in
nearly every case. Jaminet has found clots of blood in the kidneys.[2]
The mucous membrane of the stomach, intestines, and bladder is often
injected and marked with patches of ecchymosis. The lungs in cases of
true caisson disease, though occasionally found in a state resembling
red hepatization, seldom present any other change than simple
hypostatic congestion.
[Footnote 2: _Physical Effects of Compressed Air_, p. 20.]
PATHOLOGY.--It is probable that the pathology of this disease is not
entirely uniform in all cases. Doubtless the chief element in it is the
congestions already described, and especially of the brain and spinal
cord. The mechanism, therefore, of these congestions becomes a subject
of paramount importance.
It was suggested by François[3] that the morbid phenomena might be due
to the liberation in the vessels of air which had been absorbed by the
blood while under pressure, but which was set free again when the
pressure was removed. This theory has been reasserted by Paul Bert,[4]
with this difference: that he claims that bubbles of nitrogen instead
of air are the cause of the interruption of the circulation. These
bubbles he has discovered after death in the vessels of the brain and
cord. But he states that when the pressure does not exceed five
atmospheres three minutes allowed for the restoration of the normal
pressure will be found to prevent the formation of these globules of
nitrogen. Now, we find the caisson disease occurring when the pressure
does not exceed two atmospheres and when six to eight minutes are
allowed for locking out.[5] It would seem that under these conditions
the gas should escape through the lungs as rapidly as it is disengaged
from the blood. Moreover, we find that the attack often comes on
several minutes or even hours after leaving the caisson. During this
time any free nitrogen in the blood should be constantly becoming less
by diffusion through the {856} pulmonary membrane, and if enough were
not present at first to cause obstruction, such an effect could
scarcely take place at a later period.[6]
[Footnote 3: _Annales d'Hygien publique et de Méd. legale_, t. xiv.,
1860.]
[Footnote 4: _Comptes Rendus_, August, 1872, and February and March,
1873.]
[Footnote 5: _I.e._ passing from the caisson into the open air through
the lock, or antechamber, where the pressure is gradually reduced.]
[Footnote 6: In a private letter to the writer, T. Lauder Brunton
suggests that a bubble of air might pass from a larger vessel, which it
had only partially obstructed, into a smaller branch, which would be
entirely occluded by it, or that additional nitrogen might be
disengaged when the pressure was lessened by relaxation of vascular
tension.]
It is also very difficult to reconcile with Bert's theory the fact of
the comparative immunity from danger which results from repeated
exposures to the effects of compressed air. If the action were that of
purely physical causes, habit could make no difference. The obstruction
of the vessels, as described by Bert, is a condition of which the
system could never become tolerant by frequency of repetition.
In the writer's view, the explanation is to be found in the changed
conditions of the circulation, which result first from the increased
pressure upon the surface, and then from the sudden removal of the
pressure. While the subject is in the caisson the blood is driven from
the peripheral vessels toward the interior of the body, where the
pressure is less than at the surface.[7] It is also forced from the
more compressible tissues into the solid and resisting organs, such as
the liver and kidneys; and lastly, it flows toward bony cavities, for
the reason that their walls resist the effect of direct pressure, and
equilibrium of pressure can be restored within them only by an afflux
of blood. Thus the distribution of the blood is everywhere changed, and
the size of the vessels is no longer determined by the muscular action
of their walls, but by the amount of blood forced into them, the vital
action which should regulate the circulation being entirely overpowered
and set at naught by an overwhelming physical force operating from
without. The vessels become merely passive tubes, distended in some
places where they are protected from pressure, and compressed in others
where the tissues about them are compressible. By this transfer of
blood from one part to another the equilibrium of pressure is restored
and the circulation goes on, though without any regard to the
physiological demands of the different organs. There is no stasis
anywhere so long as pressure and counter-pressure are equal, thus
allowing fair play for the action of the heart.
[Footnote 7: This is shown by the marked pallor of the skin and the
shrunken and wrinkled appearance of the hands.]
If, now, the external pressure is suddenly removed, what will be the
result? Vessels which have been compressed and almost emptied of blood
will now offer new channels through which the blood can rush, and
vessels overcrowded with blood, with their walls paralyzed by
over-distension, will have the current within them slowed almost or
quite to the point of stopping. The vessels of the brain and spinal
cord, being within bony walls, where the direct pressure of the
condensed air could not affect them, will be found the most distended
and the most helpless to relieve themselves. They will get little aid
from the vis a tergo of the circulation, for the blood will find easier
courses by other ways, vascular tension being almost nil and the
vaso-motor system out of use.
The longer the sojourn in the caisson has been, the more entirely
passive the vessels will have become, and the longer will be the time
they will require to resume their normal condition. At some points the
circulation will be greatly slowed or entirely interrupted, and
nerve-elements lying beyond and deprived of their blood-supply will
express their want by pain or paralysis. Areas of stasis once formed
will be likely to extend, and may thus affect nerve-elements which at
first escaped. This would explain those cases in which the attack is
deferred until some time after leaving the caisson.
It is readily conceivable that in persons beginning work when the
pressure is slight and continuing day by day, as the pressure slowly
increases the {857} vessels should acquire the power of adaptation to
the variations in the amount of their contents, since this is only an
extension of the physiological principle which we see exemplified in
all organs having an intermittent function.
The influence of the trophic system of nerves also, as the connecting
link between central nerve-lesions and peripheral vascular
disturbances, must not be forgotten in this connection. Suspension of
function in trophic cells, either in the cerebral cortex or in the
anterior horns of the cord, could easily be brought about by the action
of the mechanical causes already described, and would result in areas
of vaso-motor paralysis and consequent congestion at the termination of
the corresponding nerve-fibres. The proneness of the large joints, and
especially the knees, to be attacked is suggestive, in view of the like
circumstance in chronic degeneration of the cord.
CAUSES.--The one essential cause without which the disease can never be
developed is transition to the normal atmospheric pressure after a
prolonged sojourn in a highly-condensed atmosphere. Hence we have to
consider two elements, pressure and time, the danger in these cases
being as the degree of pressure to which the person has been exposed
multiplied by the duration of the exposure.
But inasmuch as a prolonged sojourn in the caisson does not in every
case produce the disease (many of the men employed escaping it
entirely), it follows that there must be concurrent causes which
determine its development.
The first of these is a special predisposition. This is occasionally
strongly marked, some persons being affected by a short exposure to a
low pressure from which there would generally be experienced no
inconvenience whatever.
Perhaps the most frequent exciting cause of the caisson disease is too
rapid locking out. Indeed, it is altogether probable that if sufficient
time were allowed for passing through the lock the disease would never
occur. But what is sufficient time for one is too short for another;
and all that can be done is to fix upon a duration for the process
which shall be proportioned to the pressure, and as great as is
consistent with the circumstances, and then to see that the rule is
rigidly observed. At least five minutes should always be allowed for
each additional atmosphere of pressure.
Newness to the Work.--Unquestionably, the liability to the caisson
disease is greatest in those exposed for the first time to the
influence of the compressed air. New hands are very apt indeed to
suffer more or less during the first week. Those least affected are
such as begin work when the pressure is comparatively slight, and
continue without intermission as the pressure increases. It seems that
the system after a time becomes adapted to the changed conditions, and
is protected in a measure from their effects. Nevertheless, some
serious cases occur among old hands, especially when for any reason
their stay in the caisson is prolonged beyond the usual time, thus
showing that their immunity is merely relative. A sudden increase of
pressure also, even though very slight, is certain to develop new
cases, men thoroughly inured to the work often being affected under
such circumstances.
Fulness of Habit.--During the progress of the work on the East River
Bridge in 1872 the writer, who had medical charge of the men, observed
that among those taken sick there was a very marked preponderance of
men of heavy build and with a tendency to corpulency. Of 39 men of this
build, only 3 escaped illness, while of 53 lank and spare men 25
escaped. Of the 39 stout men, 8 were more or less paralyzed; of the 53
slender men, only 2 were paralyzed. The deaths, 3 in number, were all
of heavy men.
These figures show unmistakably that a tendency to fulness of habit
renders work in a compressed atmosphere much more hazardous. Persons of
this build have more fluids in the body, the distribution of which is
changed by the pressure in the manner before stated, and it is
therefore not surprising {858} that the effect upon them should be
greater than upon lean and sinewy persons, whose bodies contain a
minimum of fluid.
Severe Exertion immediately after Leaving the Caisson.--As at the
moment of going out of the compressed air the system undergoes a
violent reaction, it is manifestly unfitted to bear in addition a
severe tax upon the muscular strength. Hence the ascent of a long
flight of stairs immediately after leaving the air-lock is as wrong in
theory as it has proved bad in practice. Triger, whose apparatus at
Chalonnes was so arranged that the ascent of the ladder took place in
the compressed air, the lock being placed at the top instead of the
bottom of the shaft, found that the men ascended a distance of seventy
feet without becoming in the least out of breath--making the ascent, in
fact, more easily than if it had been in the open air.[8]
[Footnote 8: _Comptes Rendus_, t. xiii., 1841.]
The Abuse of Alcohol.--Several writers have remarked that habitual
drinkers are more likely to be affected than those who used spirits
moderately or not at all. It is stated by the director of the work at
Douchy[9] that the attacks from which the men suffered were "almost
always coincident with some excess committed in the interval of the
shifts." It is easy to perceive that, as the disease is characterized
by cerebral congestion, the abuse of alcohol, which has a tendency to
produce the same result, would act as a predisposing cause.
[Footnote 9: _Annales d'Hyg. pub. et de Méd. legale_, 1854.]
Entering the Caisson Fasting.--Jaminet insists very strongly upon the
influence of this cause, and cites instances to prove his position.
Several cases corroborative of his views occurred under the observation
of the writer. One of the rules for the men working in the New York
caisson prohibited entering the compressed air without having taken
food, and in addition to this each new hand was especially cautioned as
to the danger of disregarding this precaution, and the foremen were
directed to use every effort to secure its observance. Yet,
notwithstanding all this, a number of very severe attacks were found to
be coincident with, if not dependent upon, violations of this rule. In
these cases epigastric pain and retching were prominent symptoms.
TREATMENT.--The treatment of this disease will depend upon the severity
of the case and the presence or absence of gastric symptoms or of
paralysis. If we have to deal with the neuralgic pains only, the chief
reliance must be upon anodynes administered with a liberal hand.
Fortunately, the pain, though very severe while it lasts, is in most
cases of short duration, the attack passing off usually in a few hours.
It is therefore quite practicable to keep the patient under the
influence of morphine during the whole time, and thus enable him to
escape entirely all extreme suffering. But large doses will be
required, the intense pain inducing a remarkable tolerance of the drug.
Half a grain may be given at the outset, and a quarter of a grain every
half hour afterward until relief is obtained. When employed
hypodermically somewhat smaller doses may be used.
In some instances the very best results are obtained from hypodermic
injections of atropine at the seat of pain, but in other cases they
fail to procure relief, and, upon the whole, atropine is inferior to
morphine.
Jaminet, regarding the affection as wholly the result of exhaustion,
relies entirely upon stimulants and concentrated nourishment, ignoring
the aid of anodynes altogether. It is difficult to see the reason for
this, even admitting to the fullest extent his theory of the disease,
for nothing can be more exhausting than the intolerable pain which
characterizes this affection, and nothing could act more promptly as a
restorative than an efficient anodyne.
Starting from the theory already given as to the mode in which the
disease is produced, the writer was led to the idea that benefit would
be derived from {859} the use of an agent that would induce contraction
of the capillaries, and thus correct the want of tone which was
considered to lie at the foundation of the difficulty. For this purpose
ergot was employed, with the belief that it would be useful, first, by
contracting the vessels of the brain and spinal cord and relieving
their congested state; and, secondly, by restoring tone to the
superficial vessels, and thus imparting vigor to the circulation.
An extended trial warrants him in saying that the results justified the
theory. In his hands, though not always successful, ergot was certainly
very useful in a considerable number of cases. He has seen very severe
pain completely relieved within half an hour after the administration
of a drachm of the fluid extract. In other instances unsteadiness of
the limbs, which seemed about to usher in paralysis, yielded promptly
to one or two doses. A teaspoonful of the fluid extract may be given,
and the dose repeated in half or three-quarters of an hour, unless the
pain is relieved.
Frictions, with or without stimulating liniments, are very generally
resorted to, and seem sometimes to give momentary relief, but it
appears to be rather by occupying the attention of the patient than by
any action occasioned in the part. In some instances, when the pain is
confined to a particular locality, having the part immersed in hot
water will afford temporary relief. But the use of the general hot bath
is not advised, as it is unsafe to increase the already existing
relaxation of the vessels. In several of Jaminet's cases paralysis came
on while in the hot bath. In two of the writer's cases cold was applied
to the spine, with apparent benefit in each.
Epigastric pain is almost always relieved at once by the use of an
alcoholic stimulant with ginger, as employed by Jaminet.
Vomiting is best treated with sinapisms to the epigastrium and
swallowing small bits of ice.
When paralysis occurs it is to be treated on general principles. Cups
or leeches, with douches and frictions to the spine, may be useful;
and, if the case be protracted, the use of strychnine may be called
for. Electricity may be of service in preserving the nutrition of the
muscles. The bladder will almost certainly be involved, requiring the
constant use of the catheter.
The cerebral symptoms which occasionally occur are, with the exception
of coma, so transient in their nature as to call for no special
treatment. Coma, when it takes place, is to be managed according to the
circumstances of the case, as when proceeding from other causes. If
accompanied by a full, strong pulse, venesection may be expedient.
There remains to be considered a plan of treatment originally suggested
by Pol, and carried out to some extent by Foley--viz. returning the
patient at once into the compressed air. Foley says, as the result of
his experience, "A true specific is returning to the caisson, through
which means all such accidents (pains, vertigo, etc.) speedily
disappear. It is to be resorted to unhesitatingly in all threatening
cases, and the pressure should be admitted rapidly." But the means of
access to the caisson are usually such that it would be difficult to
remove a patient into it, even if he could be comfortably cared for
while there or if his presence would not interfere with the work. It
would therefore be desirable to have facilities for employing
compressed air at some point above ground which would be easily
accessible.
Of course the secondary effects which arise in protracted cases would
not be capable of direct relief by simply reproducing the physical
conditions existing in the caisson. The most that might be hoped for in
such cases would be that the pressure might result in giving a new
impulse to the circulation in the congested part, and thus favor
resolution.
Reasoning from his view of the pathology of the disease, Bert has
proposed the inhalation of oxygen in order to displace the free
nitrogen from the blood by diffusion. Experiments upon animals
demonstrated that the sounds {860} produced in the heart by the
presence of free nitrogen speedily disappeared when the animal was made
to inhale oxygen, the nitrogen diffusing into this gas much more
readily than into common air. But, though immediate death was averted
by this expedient, paralysis nevertheless occurred, and the post-mortem
examination showed the presence of bubbles of nitrogen in the vessels
of the cord.
{861}
DISEASES OF THE MEDIASTINUM.
BY EDWARD T. BRUEN, M.D.
Inflammation of the Mediastinum.
SYNONYMS.--Mediastinitis. _Fr._ Médiastinite; _Ger._ Mediastinitis.
Lesions caused by inflammatory processes in the mediastinum may,
theoretically, occur in the duplicatures of the pleura, separating the
pleural from the mediastinal cavity. This condition may terminate in
resolution or in effusion of plastic lymph, as in a case reported by
Wildemann, in which the anterior mediastinum was filled with layers of
solid exudation, the pericardium inflamed, and its cavity distended by
six ounces of pus. The effusion appeared to have been occasioned by
long-continued pressure on the sternal region. The process is
practically unrecognizable during life, or at least possesses no
described clinical features.
Abscess of the Mediastinal Space.
Galen has alluded to trephining of the sternum for caries or necrosis
inducing the formation of pus; and Petit[1] has furnished many
instances of mediastinal abscess from the warfare of preceding
centuries.
[Footnote 1: _Traité des Maladies chirurgicales_, tome i. p. 143.]
ETIOLOGY.--I. Predisposing Influences.--Mediastinal abscess is very
rare, at least of such dimensions as to simulate tumor. The condition
is sometimes idiopathic, possibly due to sudden exposure to cold,[2] or
is associated with the rheumatic diathesis, but in these cases some
forgotten injury may have been received.
[Footnote 2: Gunther, _Oesterreich Zeitschrift f. Prak. Heilk._, 1859;
Gross, _System Surgery_.]
Symptomatic or secondary purulent collections may occur in connection
with operations upon the neck, as tracheotomy, also from softening
gummata or glanders, or they may be due to a constitutional cause, the
so-called metastatic inflammation of the mediastinal connective tissue
in the course of pyæmia.
Scrofulous suppuration of the lymphatic glands may result in secondary
abscess.[3]
[Footnote 3: Bristowe, _Path. Soc. Trans._, London, vol. ix. p. 46.]
II. Exciting Causes.--The mediastinum has been penetrated by balls and
sabres, and in one case the shaft of a carriage passed through the
anterior space, yet without damage to the contained viscera. Gunshot
fracture of the sternum, recorded in the history of the Civil War in
America, seems to have been very rarely followed by suppuration, even
though the tissues have been exposed to such a degree as to render the
arch of the aorta distinctly visible.
The anterior mediastinum may be threatened with inflammation, which may
sometimes terminate in abscess, as in cases of caries, necrosis, or
fracture of the sternum.
{862} Warner[4] reports a case in a boy aged thirteen in which two
weeks after fracture of the sternal bone a separation of the edges of
the fracture was observed, the interval being occupied by a tumor of
considerable size, which contracted and dilated with as much regularity
as the heart. It receded on palpation, and on removal of the pressure
the tumor immediately resumed its former size. It subsequently
ruptured, discharged the contents of an abscess, and the patient
recovered.
[Footnote 4: _Amer. Journ. Med. Sci._, Apr., 1873.]
Goodhart[5] records a case of acute mediastinal abscess resulting
apparently from injury produced by the sticking of a piece of meat in
the oesophagus. A case illustrating the possibilities of direct injury
to this region by a blow or fall has been recorded by Bennett. In a
middle-aged lady, previously in good health, an abscess slowly formed
and presented a prominence over the upper part of the sternum. Two
months before the lady had fallen in going up stairs, and struck the
sternum against the stone edge of the stairs. These examples have been
selected because they seem to cover the possibilities of directly
determining causes.
[Footnote 5: _Path. Trans._, London, vol. xxvii.]
SYMPTOMS.--There are three separate groupings under which the symptoms
may be classified: _(a)_ The latent symptoms, which include chiefly
manifestations of intra-thoracic irritation or pressure; _(b)_ the
fulminating phenomena; _(c)_ the physical signs.