Physics of Mitral and Aortic Stenosis

Disturbances of the Heart
by Oliver T. Osborne, M.D.

(Page 10 of 22)

Physics Of Mitral Stenosis

Mitral stenosis, though less common than mitral regurgitation, is a frequent form of disease of the valves, especially in women. Often this condition is associated with regurgitation; but in a simple mitral stenosis the greatest hypertrophy is of necessity in the right ventricle. The left auricle finds it difficult to empty all of its blood into the left ventricle during the ordinary diastole of the heart. This auricle then somewhat hypertrophies, but is unable to prevent more or less damming back of the blood into the lungs through the pulmonary veins. This causes passive congestion of the lungs, and the right ventricle finds that it must labor to overcome the increased resistance in the pulmonary artery, and hypertrophies to overcome this increased amount of work. When this condition has become perfected, compensation is established and the circulation is apparently normal. Nature causes these hearts, when they are disturbed or excited, to pulsate slowly, causing the diastole to be longer than in a heart with mitral regurgitation. This allows more blood to enter the left ventricle, and the left ventricle, acting perfectly on the blood which it receives, causes a good systolic pressure in the aorta and the systemic arteries. The left ventricle in this condition does not become hypertrophied. If the heart does act rapidly and the left ventricle contracts on an insufficient amount of blood, the peripheral pulse is necessarily small and the arterial tension is diminished. Very constant in this condition, and of course noticeable whenever there is pulmonary congestion, is the sharp, accentuated closure of the pulmonary valve. The lungs on the least exertion are always a little overfilled with blood. The pulmonary circulation is always working at a little disadvantage.

The first symptoms of lack of compensation with the lesion of mitral stenosis are lung symptoms - dyspnea, cough, bronchitis, slight cyanosis, sometimes blood streaks in the expectorated mucus and froth, and, if the congestion is considerable, some edema of the posterior part of the lungs, if the patient is in bed. Sooner or later during this failing compensation the right ventricle becomes dilated, and the symptoms of cardiac insufficiency and venous congestion occur, as described above with mitral insufficiency.

Again, as in mitral insufficiency, if compensation is restored in mitral stenosis, these symptoms are improved. These patients, however, are never quite free from dyspnea on exertion. Any inflammation of the lungs, even a severe bronchitis, is more or less serious for the patients and their hearts. The mucous membrane of their bronchial tubes and air vesicles is always hyperemic, and it takes little more congestion to all but close up some of the passages. and dyspnea or asthma, or suffocating, difficult cough is the consequence.

Physics Of Aortic Lesions

Next in frequency to mitral insufficiency is aortic insufficiency, which occurs most frequently in men. The cavity of the heart that is most affected by this lesion is the left ventricle, which receives blood both from the left auricle, and regurgitantly from the aorta. This part of the heart, being the strongest muscular portion, is the part most adapted to hypertrophy, and the hypertrophy with this lesion is often enormous. For a long time this large muscular section of the heart can overcome all difficulties of the aortic insufficiency. The pulse, however, will always show the quickly lost arterial pressure of every beat on account of the aorta losing its pressure through the regurgitant flow of blood. Sooner or later, from the impaired aortic tension causing a diminished or imperfect flow of blood through the coronary arteries, impaired nutrition of the heart muscle occurs. In other words, an intestinal or chronic myocarditis or fibrosis develops, with perhaps later a fatty degeneration. When this condition occurs, of course, the repair of the heart is impossible.

This form of valvular lesion is the one that is most likely to cause sudden death. In aortic regurgitation Nature causes the heart to beat rapidly. Such a heart must never beat slowly, as the longer the diastole prevails the more blood will regurgitate into the left ventricle, and death may occur from sudden anemia of the base of the brain. Such a heart may, of course, receive a sudden strain, or the left ventricle may dilate, and yet serious myocarditis or fatty degeneration may not have occurred.

The signs of lack of compensation are generally cardiac distress, rapid heart, insufficiency of the systolic force of the left ventricle, and therefore impaired peripheral circulation, a sluggish return circulation, pendent edemas, and soon, with the left auricle finding the left ventricle. insufficiently emptied, the damming back of the blood is in broken compensation with the mitral lesions.

Aortic Stenosis

Aortic narrowing or stenosis is a frequent occurrence in the aged and in arteriosclerosis when the aorta is involved. It is not a frequent single lesion in the young. If it occurs in children or young adults, it is likely to be combined with aortic regurgitation, meaning that the valve hay been seriously injured by an endocarditis.

The first effect of this narrowing is to cause hypertrophy of the left ventricle, and as long as this ventricle is able to force the blood through the narrowed opening at the aortic valve, the general circulation is perfect. Nature again steps in to cause such a heart to heat deliberately, allowing time for the contracting ventricle to force the blood through the narrowed orifice. The blood pressure may be sufficient, or even increased if arteriosclerosis is present, although the rise of the sphygmograph tracing is not so high as normal. If the pressure in the aorta is sufficient from the amount of blood forced into it, the coronary arteries receive enough blood to keep up the nutrition of the heart muscle. Sooner or later, however, the left ventricle will become weakened, especially when there is arteriosclerosis or other hypertension, and chronic endocarditis and fatty degeneration result. If the left ventricle becomes sufficiently weakened or dilated, the same damming back of the blood through the lungs and right heart occurs, and more or less serious signs of broken compensation develop. The main danger, however, with a heart with this lesion, occurring coincidently with arteriosclerosis, is a progressive chronic myocarditis.