Physiological Researches on Life and Death

by Xavier Bichat

But whatever be the state of the lungs in the asphyxiated subject, the venous system is full of black blood, especially about the heart. In this respect, there is always a very wide difference between the veins and the arteries, and accordingly the blood must find in the lungs the principal obstacle to its circulation: such obstacle, as we have said, does not proceed from the tortuosity, and state of collapse in the pulmonary vessels; its causes are relative, first to the blood, secondly, to the lungs, thirdly to the heart.

The principal cause depending on the blood, consists in the great quantity of this fluid, which passes from the arteries into the veins. In fact we shall soon see, that the black blood when it circulates in the arteries, is not capable of furnishing the materials of secretion, exhalation, or nutrition, or if it be so, that it is not a stimulus to the organs which are the agents of these functions.[86]

It follows as a necessary consequence, that the portion of fluid which is usually taken up from the arterial system by these different functions, flows on into the venous system, together with the portion which should naturally pass thither; hence there must be contained a greater quantity than usual in the veins; and therefore a greater difficulty be experienced in its passage through the lungs. Practitioners in opening the bodies of asphyxiated persons, have always remarked the abundance of blood which is met with there. The fact has been particularly remarked by Portal, and I have always found it in my experiments.

The causes of obstacle to the passage of the blood proceeding from the lungs, are first the non-excitement of this organ by arterial blood. In asphyxia, the bronchial arteries are penetrated by the black blood as well as the rest. Hence its obscure and dusky colour in this case. This colour and its successive shades, may be easily remarked in the collapsed lung, when the chest is opened; but in asphyxia, such blackness is principally owing to the colour of the blood, contained in the pulmonary veins.

The black blood when circulating in the bronchial vessels, produces upon the lungs the same effect which it does in the heart, by penetrating the coronary arteries; it weakens the different parts—impedes their action, and the capillary secretions which should be made there, from the tonic powers of the organ.

The second cause of obstacle to the circulation, when the chemical functions of the lungs are interrupted, is the non-excitement of the organ by vital air. The first effect of such air upon the mucous surfaces of the air-cells, is to stimulate them, and so to keep them up in a sort of perpetual erethism.[87] In the same way are the powers of the stomach brought into action by the presence of aliment there, and those of every reservoir of the body, by the influx of their accustomed fluids. Again, such excitement of the mucous surfaces by foreign substances keeps up their tone. The privation of such excitement, therefore, must put a stop to their capillary secretions, which depend upon their tonic powers.

The different aeriform fluids which take the place of the atmospheric air in the different sorts of asphyxia, appear to act very differently upon the tonic powers, or the insensible organic contractility of the lungs. Some of these put a sudden stop to the circulation, others not. Compare the asphyxiæ produced by nitrous or sulphurated hydrogen gas, with those which may be occasioned by pure hydrogen, or carbonic acid gas, and the difference will instantly be seen. This difference indeed, as well as the various other phenomena observable in the various asphyxiæ, depends on causes which we have not mentioned, but the affection of the air-cells, is evidently one of them.

Lastly, the third cause of stagnation of the blood in the venous vascular system, is that debility, which takes place in the ventricle and auricle of this system, when penetrated with venous blood: on the influx of the blood from the cava, they are consequently distended, and this is the case also with the cava itself, for the very same reason. The causes which are now assigned, are sufficient to shew why the black-blooded system, is gorged with fluids in asphyxiæ.[88] The following considerations will shew why the red-blooded system contains a lesser quantity of fluid.

1st.—The obstacle commences in the lungs; therefore the aortic heart must receive a less quantity than usual: hence, as we have seen, proceeds the quicker cessation of the contractions of this ventricle.