The hypertrophy of the left ventricle in connection with contracted kidneys is more frequent and more marked. Traube suggested44 that the interference with the local circulation in the kidneys by the obliteration of vessels increased the work of the heart and induced the hypertrophy, but it is much more probable that the change is a widespread one throughout the body. Gull and Sutton hold45 that in these cases there is a condition of arterio-capillary fibrosis in which the small arteries are thickened and their calibre diminished, leading in time to a more or less widespread sclerosis in various organs, particularly the kidneys. As a result of this fibrosis, the movement of blood in the smaller vessels is much impeded, the arterial tension increased, and the work of the heart greatly augmented. On the other hand, George Johnson46 maintains that the muscular coat of the arterioles becomes thickened under the influence of retained excreta, and they are in a state of spasm which increases the tension and heightens the blood-pressure in the left ventricle.
44 Gesammelte Beiträge, Bd. ii.
45 Medico-Chirurgical Transactions, lv., 1872.
46 Ibid., vol. xxxiii.
The question can scarcely be considered settled as regards details, but the general fact of increased peripheral resistance is well established, and it is one of the most frequent causes of non-valvular hypertrophy. It may be quite marked in persons without positive evidence of renal disease as indicated by albumen or casts in the urine, but in whom the condition of arterio-capillary fibrosis is evident from the thickened state of the small arteries, the increased tension, and the firm dislocated impulse of the heart.
(7) Prolonged muscular exertion has been much insisted upon as a cause of cardiac hypertrophy by DaCosta, Myers, Albutt, Seitz,47 and others. Soldiers, blacksmiths, miners, mountaineers, and men whose occupations call for heavy and prolonged exercise occasionally develop hypertrophy of the heart, which it seems reasonable to connect with the over-use of the muscles. DaCosta's irritable heart in young soldiers appears to represent the early stage of this condition. In 38 per cent. of the cases excessive marching was the cause. He was able to confirm the existence of hypertrophy by autopsy. It is not uncommon to meet with cases of pronounced heart disease, with symptoms of failing compensation, dropsy, etc., in large, powerfully-built men who have been engaged in laborious occupations, and who are admitted to hospital with the clinical picture of chronic valvular disease. At the autopsy one is surprised to find an hypertrophied and dilated heart without valve lesion, perhaps no extensive arterial degeneration, and no kidney disease. They are called cases of idiopathic hypertrophy, but I believe that some of them, at any rate, are instances of a condition induced by prolonged muscular effort. I have had an opportunity of studying carefully four such cases, and I have seen autopsies in two other instances. As I mentioned, alcoholism may be also a factor in these cases, as most of them occur in hard drinkers.
47 Die Ueberanstrengung des Herzens, Berlin, 1875—a collection of six monographs on the subject.
How muscular effort acts in inducing hypertrophy has been much discussed. It seems rational to suppose that prolonged action of the heart at a rate more vigorous and rapid than normal would induce enlargement of its muscle, just as constant exercise acts with others; and possibly within limits this does take place. Albutt speaks of the large red left ventricles in the Leeds iron-workers killed by accident or cut off by acute disease. No doubt the thickness of the ventricle is measured by the muscular needs of the system. Muscular contraction affects the heart in two ways: first, the venous flow is accelerated, more blood reaches the right heart, and is sent to the lungs, and more reaches the left ventricle and the systemic arteries. The fuller inspirations also favor flow to the heart. When the exercise is excessive the right heart and the venous system become still more distended, and the outflow from the peripheral arteries proportionately retarded and the tension in them increased—particularly is this the case in efforts requiring straining, as in lifting, etc.; and, secondly, the effect of muscular contraction has been shown by Traube to increase very greatly the pressure in the arteries. Gaskell, however, states48 that when a muscle contracts its own arterioles dilate; but however that may be, the increased tension during muscular contraction can be determined in the radial by the finger, and still better by the sphygmograph, during steady contraction of the muscles of the arm. In yet a third way the blood-pressure may be increased during violent muscular efforts, particularly when the breath is held. The vaso-motor centre is stimulated by the lack of oxygen, and in consequence the blood-pressure rises in the peripheral arteries. At the end of prolonged contests we sometimes see men get pale or the left ventricle may become so embarrassed that they faint.
48 Journal of Physiology, iii.
(8) That the heart becomes hypertrophied during pregnancy has been specially insisted upon by French writers, Larcher49 and others. Many doubt the correctness of their deductions, but the weight of evidence seems to point unmistakably to the existence of moderate increase in the thickness of the walls of the left ventricle.50 Cohnstein51 connects it with the hydræmic and chlorotic conditions of the blood, so liable to develop during pregnancy.