Physiological Researches on Life and Death

by Xavier Bichat

The syncope and cold sweat still continued. Water thrown into his face, made him give some signs of life; but he died a quarter of an hour after the appearance of the accident I have just described, and forty five minutes after the commencement of the operation.

The body was examined the next morning. They expected to find the right pleura open, much blood and air effused into its cavity and the lungs on that side collapsed. Nothing of the kind was found. The pleura was whole and there was no effusion in it. The lungs were as usual; but an opening of half an inch in extent was discovered in the external jugular vein, at the place where this vein opens into the subclavian. The cavities of the heart were large but contained no blood. Bubbles of air were observed in the vessels of the brain; the other vessels were not examined.

This fact was related to me the same day, by a student who was present. It was impossible for me not to refer the death in this instance to the entrance of air into the vessels. The opening in the vein, the noise that was heard, the suddenness of the death, the absence of blood in the cavities of the heart, the presence of air in the vessels of the brain, all sufficiently indicated it. I suspected that the entrance of air had been favoured by the state of tension of the parietes of the vein, or by their morbid alteration, which did not allow them to flatten by atmospheric pressure. I thought that this phenomenon might be produced at will on animals by placing them in the same physical circumstances. I introduced then into the jugular vein of a dog, a sound of gum elastic, and I directed it towards the heart. It was hardly there before I heard the air enter the vein, and the animal fell down in syncope, with the peculiar noise which manifests the presence of air in the heart. I immediately closed the sound to prevent the entrance of more air, and the animal gradually recovered, because the quantity of air introduced had not been in sufficient quantity to produce its death. I then opened the sound, and immediately the air rushed in towards the heart, and its entrance was followed by the same consequences; but, whether from not closing the sound soon enough, or from the entrance of a greater quantity of air, the animal died unexpectedly to me. In opening it, I found all the signs of death from the sudden entrance of air. The right ventricle was distended with air mixed with a little blood.

Sometimes, without any apparent alteration in the texture of the veins, its parietes do not flatten under atmospheric pressure; a simple puncture then is sufficient, as in bleeding, to admit the air into the vessels. Lieutaud relates two cases in which it appears that this took place, and several veterinary surgeons have assured me that they have heard, after bleeding in the jugular vein, a noise which indicates the entrance of air. Usually the quantity introduced is too inconsiderable to produce any evident effects. There has been communicated to me, however, a case observed by Mr. Bouley, the younger a veterinary surgeon in Paris, in which the entrance of air was followed by effects similar to those which we have related.

Mery had long since observed, that, in opening the abdomen of a dog, and puncturing the vena cava above the origin of the emulgents, as the vein become emptied of blood, it filled with air, which went to the right ventricle. Haller also observed that air entered into the veins of frogs and other cold-blooded animals in consequence of a wound of some large vessel. He has shown that it was from this source that was derived that which Redi, Caldesi, and Morgagni saw circulating in the vessels of these animals, since it is not observed, when the necessary precautions are taken to prevent its introduction.

Nysten has made a great number of experiments upon the injection of elastic fluids into the veins, and the results which he has obtained accord perfectly with those which we have observed. He is not satisfied with injecting atmospheric air, he has introduced in the same way a great number of other gases. He has remarked, that among the gases not deleterious he can introduce, without causing death, a much greater quantity if these gases are easily dissolved in the blood.

We cannot follow him in the detail of these experiments; we shall only relate a result relative to the colouring of the blood in the lungs. He has observed, that by injecting air into the vein, so slow as not to produce the death of the animal, the colouring of the arterial blood is rendered imperfect. He is satisfied, he says, that it is not owing to the embarrassment of the lungs. The injection of oxygen does not alter this colouring. The injection of azote completely prevents it; that of the oxide of carbon does not produce any change in it. I give these results from his work; I have not had occasion to verify them myself.

[67] When air is introduced into the vena portæ, there is not only no ill effect at the moment of injection, but there usually follows no apparent effect on the animal. It is not the same when air is injected into the veins of the general system, with so much care as not to produce instantaneous death by the dilatation of the heart. The effects do not then appear till a long time after the injection; but they are wholly different from the primary effects which we have described.

These consecutive symptoms from the entrance of air into the veins are, as Nysten has remarked, the result of an obstruction of the lungs produced by the accumulation of air in the last divisions of the pulmonary artery. The embarrassment in respiration often appears at the end of half a day, it becomes greater and greater, the bronchiæ are filled with a viscid fluid; and the animal usually dies on the third or fourth day. On examination of the body, no air is found in the heart or the vessels; but the lungs, instead of being pink-coloured, are greyish, tinged with brown, and loaded with frothy blood and mucus.

Boerhaave thought, that death which follows the injection of air into the veins was always owing, as it is in this case, to the presence of the air, which offers, in the small vessels, a mechanical obstacle to the passage of the venous blood.