THE CAISSON DISEASE.'

BY ANDREW H. SMITH, M. D.

PERSONS exposed for a considerable time to a greatly increased atmospheric pressure are liable, after the pressure is removed, to certain morbid effects which comprise what is known as the caisson disease. It is observed principally in those employed in submarine operations by the aid of compressed air, and who labor for hours together in what is termed by engineers a caisson. The pressure varies with the depth at which the work is carried on, and reaches sometimes fifty or more pounds to the square inch. The disease rarely if ever occurs when the pressure is less than fifteen pounds, and its severity is, other things being equal, in direct ratio to the increase in the density of the atmosphere.

SYMPTOMS. These are, in the order of their frequency, intense neuralgic pain in one or more of the extremities, and sometimes in the trunk; epigastric pain; nausea and vomiting; more or less complete paralysis, which may be local or general; headache; vertigo; and coma.

The pain, which is often very severe, is usually paroxysmal, exacerbations and remissions occurring at short intervals. It may come on suddenly in its full severity, or it may be slight at first and rapidly increase until it becomes absolutely intolerable, " as if the flesh were being torn from the bones." The pain begins most frequently in the knees, extending rapidly to the legs and thighs, but the upper extremities may be first attacked. Sometimes the most severe pain is felt in the spine, and especially in the lumbar region. There is usually some tenderness with the pain, and a stiffness of the muscles of the affected limbs.

Epigastric pain occurs in a considerable proportion of the cases. It is often very severe, and if not relieved by treatment is liable to be followed by nausea and vomiting. The vomiting is usually limited to the ejection of the contents of the stomach, but it may persist, sometimes even after the pain has ceased. Vomiting accompanied by giddiness may occur without epigastric pain, and is then probably of cerebral origin. Paralysis, to a greater or less degree, occurs with considerable frequency, the percentage of cases increasing in proportion to the pressure of the atmosphere to which the patients have been exposed and the duration of the exposure. It affects most frequently the lower half of the body, but it may include the trunk or one or both arms. In rare cases an arm alone is affected.

The paralysis is of sensation as well as motion. It comes on soon after the invasion of the pains, but affords no relief from them. Thus, while pinching or pricking occasions no pain, the part may still be the seat of exquisite suffering. Paralysis may, however, occur in cases in which the pain is very slight or entirely absent. The paralysis varies in degree from a transient

1 This article is mostly drawn from a report by the writer on The Effects of High Atmospheric Pressure, including the Caisson Disease, published in 1873 by the New York and Brooklyn Bridge Company.

weakness of the limbs and slightly impaired sensation to complete loss of motion and sensation in the affected part. Even the minor degrees generally affect the bladder.

Symptoms of a transient character are often observed depending upon changes in the brain. They consist of headache, dizziness, double vision, incoherence of speech, and sometimes syncope. They usually pass off in a few hours. In fatal cases, however, coma is the usual forerunner of death. The duration of the caisson disease is from three or four hours to six or eight days. When paralysis occurs it may continue for weeks, or it may pass off within twelve hours. The cases marked only by neuralgic pains do not generally last more than six to twelve hours, though some continue five or six days. Death occurs only in cases which are severe from the first and show symptoms of cerebral or spinal effusion.

MORBID ANATOMY.-The constant lesion in fatal cases of caisson disease 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.

every case.

Congestions also occur in other localities, and especially in the solid abdominal viscera. The liver and spleen have been found engorged in nearly Jaminet has found clots of blood in the kidneys. 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.

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' 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,' 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." 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 pulmo

1 Physical Effects of Compressed Air, p. 20.

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Annales d' Hygien publique et de Méd. legale, t. xiv., 1860.

Comptes Rendus, August, 1872, and February and March, 1873.

I. e. passing from the caisson into the open air through the lock, or antechamber, where the pressure is gradually reduced.

nary membrane, and if enough were not present at first to cause obstruction, such an effect could scarcely take place at a later period.'

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. 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.

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 ves

1 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.

2 This is shown by the marked pallor of the skin and the shrunken and wrinkled appearance of the hands.

sels 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 what

ever.

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

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.'

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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 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.

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 1 Comptes Rendus, t. xiii., 1841.

2 Annales d'Hyg. pub. et de Méd. legale, 1854.