ARTERIES, DISEASES OF. Apart from their implica tion in neighbouring foci of disease, e.g., abscess or new growth, arteries suffer from certain well-defined morbid processes whereby the character of their walls is affected and changes may be in duced in the tissues they normally supply with blood and in the heart which pumps that blood along them. The chief of these processes are atheroma, arterio-sclerosis, syphilitic endarteritis (endarteritis obliterans), embolism and thrombosis. In addition the normal diameter of the arteries may be altered by nervous causes as in shock, various paralytic states, Raynaud's disease (q.v.) and by surgical or accidental means as in ligature.
In atheroma a local proliferation of endothelial cells takes place in the arterial wall at the junction of the middle and inner coats and later undergoes fatty or caseous degeneration. The degenerated material may ultimately be discharged into the lumen of the vessel, an atheromatous ulcer being formed, or it may be come infiltrated with calcium salts when its site is represented by a calcareous plaque in the wall of the artery. Atheroma is com monest in the aorta including the aortic valves and the incidence increases with age ; it chiefly affects males and small innocuous patches are present in most men above the age of 5o. The atheromatous ulcer may become the starting point of an aneurysm (q.v.) or of embolism from dislodgment of a fragment of fibrin deposited on the floor of the ulcer by the circulating blood. If the atheroma be so extensive that small as well as large arteries are involved, the calcareous process is likely to convert a vessel such as the radial or tibial into a rigid tube in which thrombosis (q.v.) occurs and leads to local gangrene. Where atheroma affects the aortic valves and leads to stenosis or regurgitation the heart reacts to the valvular condition by dilatation and hyper trophy (q.v.) as in similar non-atheromatous cases. Even ex tensive atheroma of the aorta does not introduce any factor modi fying the work of the left ventricle unless at the same time the orifices of the coronary arteries be narrowed. Under the last mentioned condition nutrition of the cardiac muscle and en docardiac ganglia is impaired, fatty degenerative changes occur and anginal attacks are probable (see ANGINA PECTORIS). When calcareous atheroma affects extensively the smaller arteries, the rigidity and diminution of calibre introduce an obstacle in the peripheral resistance which the heart cannot overcome by in creased work. Hence the left ventricle does not hypertrophy. Indeed the age of the patient and the general conditions are such that the heart in these cases is small, feeble and somewhat dilated.
In arterio-sclerosis the smaller arteries throughout the body become thickened and their lumen narrowed by the formation of an increased amount of fibrous tissue, and possibly of the muscu lar elements, in the middle coat. In the first instance, at all events, the inner and outer coats are unaffected. The condition leads to hypertrophy of the left ventricle owing to the increased periph eral resistance introduced by the narrowed, but still distensible arteries, and the general blood pressure rises. The arterioles of the kidney share in the general change and the organ shows the fibrotic and parenchymatous changes constituting chronic granu lar kidney (see KIDNEY, DISEASES OF). The clinical symptoms of arterio-sclerosis are therefore those of heightened arterial tension together with those of renal fibrosis, complicated later by the car diac changes the hypertrophied heart undergoes when compen sation fails (see HEART, DISEASES OF) . Apart from these changes the altered blood vessels are, themselves, liable to undergo de generative processes identical with or resembling those occurring in atheroma, and where relatively unsupported as in the lenticulo striate region of the brain, small aneurysms are often formed, one of which may rupture under the force of the ventricular systole and lead to cerebral haemorrhage (see APOPLEXY). Such so-called miliary or millet seed aneurysms are of pin-head size. Haemor rhage may also occur into the retina, the semi-circular canals and the intestinal mucosa. In the eye they lead to varying degrees of impaired vision according to their extent and situation and in the ear to Meniere's disease (q.v.). One feature of all these haemorrhages is that they are liable to be repeated owing to the permanent character of the underlying arterial and cardiac changes. In an autopsy upon a case of fatal cerebral haemor rhage evidence of earlier small haemorrhages into other parts of the brain is often found.
In syphilitic endarteritis or endarteritis obliterans the inner coat of the artery is the seat of a localized but of ten widespread inflammatory proliferation of endothelial cells with an admixture of lymphocytes. Such foci involve a portion of the circumference of the vessel and thus narrow the lumen and make it irregular in shape. They are avascular, and caseous degeneration early occurs with the result that the superficial endothelium dies and local thrombosis occludes the lumen completely. Affecting the large arteries the condition is highly diagnostic but rarely gives rise to symptoms. In arteries of small calibre, on the contrary, especially those of the brain, it is of grave importance ; in young adults symptoms of "apoplexy" almost invariably are due either to syphilitic endarteritis with thrombosis or to em bolism. What relation this form of endarteritis bears to atheroma is uncertain. In well-marked instances of syphilitic endarteritis soft flattened excrescences from the smooth inner lining of the arteries occur in numbers and distribution recalling those of wide spread calcareous atheroma, and it may be that the latter condi tion is a late stage of the former. Indeed many cases of syphilitic endarteritis were described as "soft atheroma" before the Tre'. ponema pallidum was discovered.
Apart t rom rupture with its associated haemorrhage, aneurysm with its special pressure effects and liability to rupture, and ar teriosclerosis with its associated renal and cardiac changes, disease of an artery is important mainly because of the thrombosis it provokes and the nutritive changes that its occlusion may in duce in the tissues it supplies. As is shown elsewhere (see THROMBOSIS) the effects of occlusion depend upon whether the occluded vessel anastomoses freely or not and whether the con dition is septic or aseptic.
The treatment of arterial diseases is mainly that of the con dition upon which they depend or of the states to which they give rise. For the arterial condition itself no treatment is available except in some cases of aneurysm where thrombosis may be in duced by ligature of the vessel. In arteriosclerosis the ill effects of high arterial tension, renal inadequacy and the excessive work thrown on the heart are combated by eliminating as far as possible the external conditions that favour the occurrence of these ill effects. Thus, muscular exertion is reduced, diet is restricted, sleep is encouraged and, in order to relieve the kidneys, adequate action of the skin and intestines is promoted. In atheroma where gangrene occurs the treatment is that of the gangrene combined with such general treatment as is required by the age and cardiac weakness of the patient.
See T. McCrae, Osler's Modern Medicine; Tice, Practice of Medi cine; Allbutt and Rolleston, System of Medicine. (W. S. L.-B.)