A system of practical medicine. By American authors. Vol. 3

by Unknown

Cyanosis.

There are two views to be found, set in opposition to each other, to account for the peculiar blue coloration of the skin and mucous membranes in cases of malformation of the heart. The first explanation attributes the phenomenon to a general congestion of the venous system, due to the obstruction of the pulmonary artery. This view was proposed by Morgagni in connection with his, the first described, case of malformation of the heart. The other view considers that the intermingling of venous and arterial blood through any channel, but especially by means of abnormal openings in the septa, produces the blue coloration. Numerous writers have defended each of these theories of causation; from most of their observations darkness rather than light has resulted through the attempt to defend one or the other theory exclusively.

Gintrac defended the admixture theory for cyanosis, and his views became so well known that a large majority of persons conformed their belief to his teachings. This author distinguished four varieties of blue coloration: first, that due to some malformation of the heart or great vessels, by which the blood of the right side of the heart enters the systemic arterial circulation; second, likewise due to intermixture of the blood, but produced by conditions developed after birth through the re-establishment of the passages of communication or other changes in the circulation; third, where the coloration appears without direct admixture of the blood, but from organic disease of the heart; fourth, cases without malformation, from a suppression of the menses. Before the time of Gintrac, cyanosis had a very indefinite signification, and the condition was looked upon, and was classed by very many, as one of the cachexiæ, and was often spoken of as a form of icterus. He, however, held that the organic lesions of the heart and great vessels were the necessary conditions of its production, and that the mixture of the red and black blood, and the distribution of the mixed fluid by means of the arteries to all parts of the body, determined its essential character. He showed, too, that all communications between the right and left heart were not followed by cyanosis; the explanation of the absence of the blue color was that from the simultaneous contraction of the auricles and ventricles of the two sides of the heart an equilibrium was produced, and the blood did not deviate from its normal course. This result followed only when the normal exits of the blood were unobstructed. This supposition, as is apparent, is not in accord with the facts. During the filling of the ventricles, before the muscular contraction of the walls occurs, the blood has the opportunity of freely mingling if the opening between the cavities is sufficiently large: that the blood will not thus mingle when the muscular contraction acts remains to be proved. Cases of open septum ventriculorum, as an isolated defect, without obstruction of the great vascular trunks (a rare condition), are not attended with cyanosis: the absence of this symptom, as will be shown later, is readily to be explained on other grounds than those supposed by Gintrac. The normal outlets of the blood are, however, almost always obstructed to a greater or less degree; and here the explanation of the absence of the cyanosis fails. In the delayed appearance of cyanosis Gintrac considered the reason to be that the venous blood differed less from the arterial in the young subject than in those of more advanced age, because, on the one hand, the aëration was more active, and, on the other hand, the deterioration of arterial blood was less marked. In other cases he points to an increase of the obstruction, through inflammatory changes, as the probable reason for the delayed appearance of the blue color; in still other cases it was supposed to be due to a disturbance of the equilibrium of the pulmonary and systemic circulation from an increase in the blood-mass. In cases of unilocular and bilocular hearts, of which the author speaks, his explanation completely fails, for here the admixture of the blood within the heart is very marked; yet such cases have been reported without cyanosis. He further believed that openings in the ventricular septum, as well as between the auricles, were effected after birth as the results of acquired cardiac disease.

Gintrac, in speaking of the causes of cyanosis, says that the condition shows no hereditary tendency; that the pregnancy during which the defective infant is developed is without noticeable phenomena; and that the confinement is normal. It is on some of these points that we are in want of accurate information. It has been pointed out that many congenital defects of the heart result from morbid processes affecting the organ during its developmental stage. These lesions are the same in kind as those which produce cardiac and vascular disease in the adult, and are likewise of a sort capable of communication from the parent to the foetus. Such diseases are found acting oftentimes temporarily in the parent; and if they acted during pregnancy, or even if present only at the time of conception, their results would rationally be expected to be displayed in the foetus. Such diseases as rheumatism and syphilis, which may be regarded as temporarily-acting maladies, would come under this class, and doubtless many others might be added to the list. The work of collecting the histories of pregnancies or the condition of the parents at or before the time of conception would be painfully tedious: such records do not exist at present, and they could be made sufficiently full only in exceptional cases; but their value in determining the causes which operate in the production of defective development of the heart cannot be too highly estimated.

The conclusions stated by Moreton Stillé⁹ seem to be the first which justly cover the ground from a comparison of large numbers of cases of malformation of the heart. The first conclusion by him is that cyanosis may exist without admixture of the blood; by this was meant that no abnormal communication between the right and left sides of the heart, and no channels between the principal vascular trunks, are present. He mentions five cases of cyanosis occurring in which no means of admixture existed. The second conclusion is that there exists no proportion between cyanosis and the degree in which the blood is mixed; for this he cites four cases, some with the aorta arising from the right ventricle, others of hearts with only two cavities and the common trunk undivided, in which the cyanosis was only partial or transient. The third conclusion, the converse of the first, and reinforcing the preceding one, is that complete admixture of the blood may take place without cyanosis. The fourth, that the variation in the extent, depth, and duration of the discoloration is inexplicable by the doctrine of the mixture of the blood.

⁹ "Inaug. Thesis." Amer. Journ. Med. Sci., N. S., vol. viii., 1844.

Having shown that commingling of arterial and venous blood cannot be the cause in itself of cyanosis, Stillé proceeds to the study of the other theory—viz. that it is due to congestion of the general venous system resulting from some obstruction in the right side of the heart or in the pulmonary artery, impeding the passage of the blood through the heart. These structural lesions must fulfil the three following indications: 1st, that they shall be sufficient in degree to account for the symptom; 2d, that they be present in every case of cyanosis, or in their place some other cause acting on similar principles; 3d, that they shall never exist without cyanosis or without a satisfactory explanation of the exceptional occurrence. He holds that contraction of the pulmonary artery is to be taken as the type of all the lesions that may produce cyanosis, and that this type fulfils the indications given above.

Most writers since Stillé have coincided with him, or have regarded cyanosis as partly due to venous congestion and partly to commingling of arterial and venous blood. Some writers, however, have pointed to the abnormal communications between the right and left side of the heart, and asked why, if admixture of the venous and arterial blood is not the cause of cyanosis, should the admixture through such openings be found in such a large proportion of cases. Such writers have failed to distinguish between the primary and secondary defects of development. They have failed to see that the pulmonary obstruction which prevents the blood during extra-uterine life from passing to the lungs for aëration, and consequently produced the cyanosis, prevented the closure of the ventricular septum during intra-uterine life, or of the auricular septum within a few days of birth. In reply to the above question it may be pointed out, as Peacock has done, that such communications between the two sides of the heart are all important for the continuance of life, even for the shortest period, when the pulmonary artery is occluded.

It is evident, as Peacock has shown, that if Stillé's first and third conclusions are true, as the cases undoubtedly show, the theory of intermixture of the blood does not account for the condition of cyanosis. It is probable in many of these cases with abnormal openings in the septa that the intermixture of the blood is but slight, since if the pressure on the two sides of the heart is equal—and it may become equal through the establishment of a collateral circulation, although primarily it was unequal—no intermixture takes place through the defective septa. Neither does the admixture theory account for cases of intermittent or delayed cyanosis. Such cases can only be supposed to be due to a varying propulsive power or to a subsequent increase of the pulmonary obstruction. Neither does admixture account for localized cyanosis; for example, in the face or in one extremity: this condition, rare as it is, must be due to other causes. Peacock, while combating the admixture theory, considers that Stillé's conclusions in favor of the congestion theory as dependent on obstruction of the pulmonary artery are too exclusive. He discusses also the relationship of congenital cyanosis due to malformation, to cyanosis acquired through pulmonary and cardiac disease as seen in the adult, and shows why the latter condition is rarely ever as intense as the former, and also why acquired obstruction of the pulmonary artery is not necessarily productive of cyanosis. The reason of the difference he believes consists in the compensatory hypertrophy of the right ventricle, with perhaps a gradual diminution of the blood-mass, as seen in some cases.

On the whole, Peacock subscribes to the congestive theory, but thinks that the intensity of the cyanosis is modified by the capacity of the capillaries, by the period of development or duration of the obstruction, by the natural coloration of the skin, and by the color of the blood itself.