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

by Unknown

The second condition, that of diminished resistance of the walls, is found in enfeebled constitutions and in the degeneracy of tissue incident to advancing age. A familiar example is furnished by the enlargement of the veins on the back of the hand in old persons.

Excessive dilatation of the veins which go to make up the superior cava often results from insufficiency of the tricuspid valve. When this insufficiency exists a proportionate part of the systolic energy is expended in driving the blood back into the systemic venous circulation, and the superior cava, from the nearer correspondence of the axis of its opening with the axis of the auriculo-ventricular opening, receives the larger share. Hence with every contraction of the ventricle a direct distending force is exerted upon this vessel and its branches which they are not fitted anatomically to resist. In such cases the distended veins may reach an enormous size, and are seen to pulsate synchronously with the arteries. The distension is greatest in the neck, but affects also the veins of the chest and of the upper extremities.

Whenever a vein is obstructed, either by some process taking place within it or by pressure from without, the distal portion is more or less dilated. Examples of this are seen in the closure of veins from phlebitis and by the pressure of abdominal tumors or the gravid uterus.

Under like conditions the tributary veins also, being forced to carry more than the normal amount of blood, become enlarged. This we see constantly in the dilated veins of the abdomen when the internal vessels are pressed upon by large dropsical effusions.

The term caput Medusæ is applied to a collection of enlarged veins radiating from a common centre or arranged in the form of a corona. Such collections often occur on a small scale above the ankles, but under some conditions they assume vast proportions. When there is obstruction of the inferior cava a great mat or pad of dilated, convoluted veins may form on the abdomen or thighs. Some of these veins may be as large as the little finger.

In the erect posture the veins of the lower extremities are subject to a distending force proportioned to the height of the column of blood which they have to sustain. For short periods at a time the resistance of the walls is ordinarily sufficient to bear this pressure without yielding, but in persons whose occupation requires them to stand a considerable portion of each day, and especially in those past middle life, there is a gradual giving way, which results in increasing not only the diameter but the length of the vein.

The dilatation takes place irregularly, being greater at one point than at another, and in one place affecting the entire circumference of the vessel, while in another it produces a bulging on one side or even a pouch or diverticulum. Especially just above the valves in the veins of the lower extremities, where the diameter is naturally a little greater, the larger area gives rise to greater pressure, and more marked dilatation results. Their breadth remaining the same, the valves are no longer able to reach across the vein, and the circulation is deprived of the aid which it is their office to give. Instead of the column of blood being divided into a number of portions, each resting upon the valve beneath it, there is now a continuous column which exerts its full static pressure. Dilatation is thenceforth doubly rapid, and at the same time the vein is stretched longitudinally and becomes tortuous, thus adding another impediment to the circulation. The nutrient vessels ramifying in the venous walls are pressed upon, and the nutrition of the several tunica is impaired. From this arises fatty or calcareous degeneration. Under these combined influences the walls often become so thinned that rupture takes place. But it is rare that the blood is effused into the tissues surrounding the vein, for the overlying integument or mucous membrane, atrophied from the pressure of the vein beneath, usually gives way at the same time, affording a means of escape. Even bone is not capable of resisting the continuous pressure of an enlarged vein, but may be absorbed in the same way as in the case of arterial aneurism (Bristowe).

Sometimes the dilated vein becomes thicker instead of thinner by addition to the outer tunic; probably the result of a slow inflammatory process, to which, as already stated, varicose veins are peculiarly liable.

The slow circulation, especially in pouched and tortuous veins, favors the formation of coagula which frequently close up the vein entirely, thus bringing about a spontaneous cure. Independently of this, there is a disposition to recovery when the cause is removed, and the vessel may, under favorable circumstances, regain its normal condition. If, however, the valves have atrophied, as they are apt to do after their efficiency has ceased, entire recovery is impossible.

Oedema is apt to occur in connection with dilated veins if the impediment to the circulation is considerable. Chronic ulcers of the legs, accompanied by eczema, are a very common result of a varicose condition of the superficial veins of the lower limbs; and a permanent cure can seldom be effected unless the varicose condition is first removed.