Causes. The causes of arteritis are often obscure. Goubaux conceived that it was frequently determined by extreme muscular tension. In support of this view he adduced the facts that it has been mainly observed in the horse, in which such stretching of the muscles is greatest, and that its most common seats have been where the muscles and vessels are most liable to stretching. Thus it is frequent in the posterior aorta towards its termination or in other words where the adjacent muscles (psoæ) are very liable to laceration from slipping backward or from efforts to disengage the limbs when fixed in soft ground; the femoral and auxiliary arteries are likewise frequent seats of inflammation and are likely to be overstretched when the limbs slip outwards.
Embolism or Plugging of the arteries must be accepted as another cause. This is referred to under endocarditis, as an occasional consequence of the detachment of clots and fibrinous substances from the internal membrane of the heart. The detached mass in this case passes from the heart into the aorta and thence through its divisions until it reaches a vessel too small to receive it, when it is at once arrested and determines inflammatory action in the plugged vessel. When arrested in some soft organ such as the lungs, liver or brain the resulting inflammation often gives rise to extensive suppuration and abscess. In other situations its effects may be confined to inflammation, the shutting off, of blood from particular parts, the impairment or loss of their function and nutrition, and finally atrophy and degeneration.
But the heart is not always the primary source of such clots. Virchow and others have demonstrated by post mortem examinations in cases of plugging and by a number of experiments on the lower animals, not only that such clots may have their place of nativity in some distant and diseased part of the body and proceed in the veins to the heart, and thence through the arteries to other distant parts of the body where they plug the vessels and induce a train of morbid changes; but that such embolism arteritis and abscesses can be produced at will by the introduction into the circulation of solid and insoluble (infecting) bodies. Fragments of decaying and suppurating tissue and the elements of tubercle and cancer may be thus equally carried onward in the current of the circulation, and reproduce themselves at those points where their course is arrested. This is a mode in which secondary deposits of these morbid matters are determined. Embolism and arteritis in the body and limbs occurring in this way necessarily have their point of departure in pre-existing disease of the lungs. The clots loosened from the capillaries or veins of the lungs are carried through the left side of the heart into the arteries of the body at large to be arrested in some of the smaller vessels. I have seen plugging of the digital arteries of the hind limbs, to occur in this way in a horse that had been suffering from inflamed lungs.
Microbes and toxins may pass harmlessly through healthy parts, including the pulmonic circulation, to establish colonies and embolism beyond where the tissues have become debilitated. Thus Gamgee records a case of embolism of the anterior mesenteric, right external iliac and right femoral arteries, supervening on an attack of strangles.
Symptoms of acute arteritis. These consist largely in impaired muscular power in the part, indications of acute local suffering, such as trembling and tenderness to the touch, if the obstructed vessel lies within reach it can be felt as an exquisitely tender cord-like mass, and the limb on the distal side of the embolism and dependent on the diseased vessel for its blood supply is anæmic and cold. In the distal portion of the embolic artery and its branches pulsation has ceased. If the lesion is extensive there may be more or less fever, but a limited arteritis in a small vessel may escape this complication. If the disease is of long standing there is atrophy of the tissues formerly supplied by the embolic vessels. The secondary derangement of nutrition and function are as varied as the organs affected and will be noted below in the special article on thrombosis and embolism.
Chronic arteritis. Atheroma. This is an indolent inflammation supposed to result mainly from strain and overwork, and manifested by thickening and clouding of the serosa, with cell proliferation, softening and fatty degeneration. The diseased substance becomes soft, pultaceous, slightly greasy, and under molecular degeneration it breaks up and is even in part washed on in the blood stream. Other degenerations may occur in the inflamed walls of the artery. The exudate may become organized, constituting fibrous thickening. It may become the seat of calcareous degeneration. It may yield to the blood pressure, becoming slowly attenuated (atrophy), and even dilated (aneurism by dilatation). As a cause of chronic internal arteritis in the horse should be named the presence in the vessels of the larva of the strongylus armatus. The posterior aorta and anterior mesenteric artery which are the most commonly infested by these parasites are frequently attenuated, dilated and calcified in this connection.
Treatment. Acute arteritis should be treated like any other local inflammation, by rest, soothing applications (fomentations, astringents, icebags), and alkaline salts. It has been proposed to manipulate the affected artery and contained thrombus, but this can only tend to block the smaller arteries farther on, and perhaps with even more injurious results. The liberal use of alkalies on the other hand, if effective in dissolving any portion of the clot, returns this to the blood stream in a condition that will not endanger further embolism. The agents usually employed are carbonates of ammonia, potash or soda, and iodide of potassium.
THROMBOSIS AND EMBOLISM.
Definition. Thrombosis—clotting in the vessel. Embolism, blocking of the vessel. Thrombus may form in any bloodvessel. Embolism occurs in arteries. Clot follows the blood current. Causes of clotting—fibrinogen, paraglobulin, fibrine ferment; foreign bodies; parasites; air; blood that has been exposed, transfusion; ærial germs; disease germs; chemical coagulants; high and low temperatures; breaches of endothelium; congestion or inflammation of the serosa; stasis of blood and extension of clot; ligature near a branch vessel: deoxidation and carbonization of blood, marasmus; neoplasms; traumas of the vascular coats. Infarction, causes of blocking; disintegration of clots, softening, liquefaction, ulceration, action of microbes; excess of white globules; air; fat; parasites. Pathogenesis; complete occlusion of vessel; infarction; sequestrum; collateral circulation; embolism of external iliac or femoral artery; effects on pulse; during rest; atrophy; lameness comes on with exertion; disappears under rest; circulation inadequate to sustain active function. Embolism of internal iliac artery; effect on pulse; on tail and pelvic organs. Embolism of axillary artery; effect on pulse, action, nutrition. Embolism of mesenteric artery; verminous; effects on innervation and circulation; spasms, congestions, paresis; involution. Treatment: expectant; alkalies; gentle exercise, time.
Definition. Thrombosis is the blocking of a blood vessel by a clot formed in its interior by the deposition of layer above layer on its inner coat.