Cardiac muscle

“ Smooth muscle, on the other hand, is characterized by its great force, considerable rhythm, considerable tone, and slight rapidity, that is, its contraction is slower and lasts longer than that of striated muscle. Cardiac muscle is characterized by great rhythm and force, fair rapidity, and slight tonicity, tonicity being the amount of tone or readiness to work. ”

“ In such young girls we have very frequently found tight stays, which were worn unchanged without regard to the growth of the body in length, and which, by pressure on the epigastric region, elevation of the diaphragm, and limitation of the respiratory movements of the thorax, actually offered such considerable resistances to the driving power of the heart, as ultimately to lead to hypertrophy of the cardiac muscle. ”

“ TESTS OF HEART STRENGTH If both systolic and diastolic blood pressure are taken, and the heart strength is more or less accurately determined, mistakes in the administration of cardiac drugs will be less frequent. Besides mapping out the size of the heart by roentgenoscopy and studying the contractions of the heart with the fluoroscope, and a detailed study of sphygmographic and cardiographic tracings, which methods are not available to the large majority of physicians, there are various methods of approximately, at least, determining the strength of the heart muscle. ”

“ The action of the heart at first is to make it beat fuller and stronger, but if continued, the effect is also one of paralysis of its [Pg 273] muscle and a diminution of the output of work done, and finally it is a paralyzer of the heart’s action. In some persons, through its injury to the cardiac blood vessels and intrinsic muscle of the heart, it sets in motion those morbid processes which result in angina pectoris. ”

“ Such hearts always show increase in thickness of the ventricular wall. I quite agree with Stone, [8] who says, "It is merely to be emphasized that when the pulse pressure persistently equals the diastolic pressure (high pressure pulse, in other words) with a resulting 50 per cent, overload, which means the expenditure of double the normal amount of kinetic energy on the part of the heart muscle, cardiac hypertrophy has occurred." They are found in aortic insufficiency, in chronic nephritis, in the diffuse fibrous type of arteriosclerosis, and in some cases of exophthalmic goiter. ”

“ From this general discussion it is quite evident that the cardiac muscles of different animals act in very different ways and that while some, like the heart of Limulus, have a neurogenic beat, others like that of the tunicates have a myogenic beat. ”

“ The contraction of the heart, which takes place seventy to eighty times in a minute, is automatic and is due to the essential quality of the muscle which composes it. The character, frequency and force of contraction, however, can be influenced by the nervous system and by the direct action of substances upon the heart muscle. The heart is divided by a longitudinal partition into a right and left cavity, and these cavities are divided by transverse septa, with openings in them controlled by valves, each into two chambers termed auricle and ventricle. ”

“ The compressive action of the skeletal muscles returns the blood to the venous cistern, and if more arrives than can be transmitted through the lungs in a given time, the right heart becomes engorged, breathlessness occurs, and, signs of venous congestion appear in the flushed face and turgid veins. The weaker the musculature of the heart the more likely is this to occur; hence the breathlessness on exertion which characterizes cardiac affections. The training of an athlete consists largely in developing and adjusting his heart to meet this strain. ”

“ The Myocardium.—The coverings of the heart muscle cannot long be diseased without affecting the contractile substance itself. Any morbid changes in the lung tissues which impede the circulation through them, and more particularly emphysema, lead to change in the substance of the right ventricle, while morbid changes in the systemic arteries lead to changes in the left ventricle. In hypertrophy we have an increase of substance. Tangl found by direct measurement that the muscle cells are increased in diameter. ”

“ The fact that it is practically impossible to get adult, vertebrate heart-muscle free from nerve-cells has left the problem of the heart-beat in these animals in a situation difficult for experimental approach. That the heart-muscle in vertebrates is always a continuous one, the auricles and ventricles being connected by at least a slender bridge of muscle, favors the myogenic theory, as does also the fact that the beat can be reversed in that the ventricle can be made to contract first and the auricle afterwards. ”

“ Pressure in the ventricle must exceed that in the arteries before the semilunar valves will open and the blood can be driven out, just as the auriculo-ventricular valves remain closed until the pressure in the auricles exceeds that in the ventricles.
The heart beat is caused by the twisting of the heart upon its axis during contraction of the muscle. Normally it beats rhythmically and regularly, whatever a person does, at a rate of about seventy-two contractions to the minute in the adult. ”

“ This could not be true if the heart muscle had to be aroused to activity by nerves. Besides being automatic, heart muscle shows the peculiarity that whenever it contracts all the fibers join. We do not have a varying strength of pull shown by heart muscle as we do in skeletal. As we shall see, it would be a serious disadvantage rather than an advantage if heart muscle were to be like skeletal in this respect.
Smooth muscle has the duty of operating the internal organs. For this function no great strength is required; the motions do not have to be powerful. Nor is rapid motion important. ”

“ The arterial walls, which have been stretched in their diameter and in their length by exhaustion of their elasticity under the stress of cardiac systole, are strengthened afresh by the development of stays formed of fibroid and muscular tissues in the intima and media; and the heart responds to the altered mechanical condition ahead of it in the arteries, and to the increased peripheral resistance caused by the obsolescence of many capillaries, by growing afresh. ”

“ In the milder grades of fibrous myocarditis, when only the apices of the papillæ and thin layers beneath the endocardium are involved, the heart does not appear to be seriously affected; but when of any extent the vigor and force of the contractions are impaired, and the ventricle is unable to do the work of a healthy muscle. ”

“ There is increase in size of all the large distributing arteries, carotids, brachials, femorals, renals, celiac axis, etc., with fibrous changes in the media, loss of some elasticity, and increase in size of the pulse wave. Increased pulse pressure means increased volume output, but does not always mean increased velocity. The proper distribution of blood to the various organs of the body is regulated by the vasomotor system acting upon the small arteries which contain considerable unstriated muscle. ”

“ The muscle of your arm contracts only at your will. But the heart is never quiet. Awake or asleep, whatever you are doing or not doing, it keeps steadily on.
Each time the heart contracts what happens? Let us begin with the right ventricle full of blood. It contracts; the pressure comes on all sides, and were it not for the flaps that close and shut the way, some of the blood would be forced back into the right auricle. As it is, there is but one way,—through the pulmonary artery. ”

“ The heart is a hollow muscle. All the valves and division walls we have been talking about are muscular in their texture, and moved by a network of muscles and minute tendons, tough and elastic, like the gizzard of a fowl, and capable of contraction and expansion. We will suppose the right auricle to be full of blood that has been brought by the veins from the fingers, toes, the substance of the heart itself, the lungs, and the liver, and poured into it. ”

“ Too much stress can not be put on the importance of muscular exercise in regard to health, beauty and happiness. Each muscle fills with blood as it relaxes, and expels this blood on past the venous valves during contraction. Each muscle together with the venous valves forms a pump to the circulatory system. It is the function of the heart to deliver the blood to the capillaries, and the function of the muscles—visceral, respiratory and skeletal—to bring it back to the heart. The circulation is contrived for a restless mobile animal ”

“ In addition to the strength and elasticity of the wall of the arteries, which enables them to resist the pressure of the blood, they have the power of varying their calibre by the contraction or expansion of their muscular walls. Many of the organs of the body function discontinuously, periods of activity alternating with comparative repose; during the period of activity a greater blood supply is demanded, and is furnished by relaxation of the muscle fibres which allows the calibre to increase, and with this the blood flow becomes greater in amount. ”

“ We must of course accept the convulsive action of the phrenic and abdominal muscles, only it would seem that each such movement has its starting point in the contraction of the heart. In cases that show no relation in number 310nor succession with the heart beats, we can freely acknowledge a neurosis starting at a point different from the heart, but in all examples which are manifestly connected with heart movements, and readily curable by the heart-tonic digitalis, the recognition of the cardiac derangement as an initial factor is sound alike in pathology and practice. ”

“ In planning the treatment of the dilated heart of the middle-aged man who strained his circulation in youth and comes to us complaining of a recurrence of præcordial distress and breathlessness, we have to remember that there is left in the cardiac walls but a portion of that reserve of elasticity and that reserve of muscular energy which they normally possess and require to enable them to meet the stress of exertion. ”

“ Although the pericardium and heart are situated in the median plane, percussion and auscultation should be performed on the left side, since the anterior and cardiac lobes of the left lung are less developed than those of the right; but the heart can be auscultated on the right side, as is advisable at times. ”

“ In cases of cardiac weakness, the thing needed is not simply an increased rate of movement of the heart, or an increased volume of the pulse, but an increased movement of the blood current throughout the entire system. In the application of any agent for the purpose of affording relief in a condition of this kind, the peripheral heart as well as the central organ must be taken into consideration. In fact, the whole circulatory system must be regarded as one. The heart and the arteries are composed of essentially the same kind of tissue, and have practically the same functions. ”

“ In contradistinction to cross-striated muscle, the structural unit of the heart is not also a functional unit, for the heart-cells are, from the earliest stage of development, joined together by branches into networks and bands so as' to form one functional whole, and hence excitation of any one part leads to the contraction of the whole. ”

“ The implication of the fibrous structures of the pericardium and heart and especially of the valvular structures is a common lesion, and to be dreaded more than all others. In all animals this tendency to cardiac lesion is well marked, but especially in solipeds in which the great demands made on the heart during rapid paces, heavy draught, jumping, etc., severely strain the cardiac mechanism. ”

“ But when we come to consider cardiac strain a little more closely, it may be just as easily maintained that every dilated heart, every dilated cardiac chamber, every dilated blood-vessel has been strained. Whether, on the one hand, valvular disease, Bright's disease or emphysema, or, on the other hand, myocardial degeneration, has disturbed that cardinal condition of a normal circulation that the driving power must always exceed the resistance ahead, over-distension and dilatation of the cavities, with excessive stretching of their walls, constitute or consist in mechanical strain. ”

“ The beating of the heart is, of course, a succession of contractions and expansions of its muscular wall. The contraction, or systole, commences at the base of the venae cavae and passes to the auricles, driving the blood before it into the ventricles, which then contract sharply and drive it on into the aorta or pulmonary artery; a pause and then a dilatation, the diastole follows. The flow of the blood is determined in one direction by the various valves of the heart. No valves occur in the opening of the superior cavae but an imperfect one, the Eustachian valve, protects the inferior cava ”

“ The function of the cardiac nerves is to co-ordinate the beat of the heart with the needs of the body and to co-ordinate the functions of other organs with the needs of the heart. For example, an undue rise of arterial pressure, induced, let us say, by compression of the abdomen, excites the centre of the vagus and produces slowing of the heart and a consequent lowering of arterial pressure. ”

“ After the union of these two portions the muscle extends farther forwards and the fibers of the stronger portion spread out like a fan, becoming wider and thinner as they go forward and are at last attached partly to the pericardium, partly to the lobes of the liver of that side of the body. To be more exact, the fibers of the diaphragmaticus that lie nearest the middle line of the belly-wall extend forward as a fairly broad band to fuse with the pericardium. ”