1092 Valvular Diseases. 



(c) Insufficiency of the Bicuspid or Mitral Valve. 



If the two flaps of the expanded bicuspid valve do not 

 touch, a part of the blood in the left ventricle flows back into 

 the left auricle at each ventricular systole, and the blood of 

 the pulmonary veins is emptied into this auricle at the same 

 time. This causes the pressure in the auricle to be increased, 

 it becomes dilated and eventually hypertrophied, although the 

 hypertrophy is usually not very marked. But since the 

 auricular wall cannot expend the force sufiicient to remove the 

 increased pressure and since at each auricular systole blood is 

 forced into the pulmonary veins which are not provided with 

 valves, the stasis is continued upward into the pulmonary veins 

 and from these through the comparatively wide pulmonary 

 capillaries, to the pulmonary artery and the right ventricle, the 

 muscular wall of which is hypertrophied in consequence. There 

 occurs therefore an increase in blood^ pressure affecting the 

 entire lesser circulation, which is compensated in the right 

 ventricle. The persistent passive hyperemia of the lungs 

 gradually leads to the development of the socalled brown 

 induration of the lung tissue. The muscle of the left ventricle 

 ,also is usually thickened, although not greatly, because at each 

 systole it is obliged to force out a larger amount of blood. 



The heart beat is usually normal on the left side, but in- 

 creased on the right side; in horses a contraction is observed 

 commencing immediately after the beginning of the ventricular 

 systole, instead of the normal well-marked systolic rise in the 

 region of the heart during systole. Simultaneously with the 

 heart beat a systolic thrill may often be felt. The cardiac dull- 

 ness is not infrequently unchanged, but at times it is somewhat 

 enlarged on the right side, which may be seen by the fact that 

 in the fourth and also in the fifth intercostal space on the right 

 side a distinct cardiac dullness is manifest. On the left side 

 the cardiac dullness is only rarely noticeably increased. Instead 

 of the first heart sound a prolonged, blowing or rushing systolic 

 murmur is heard on the left side, the punctum maximum of 

 which is in the fifth intercostal space, in the middle of the left 

 lower third of the chest (Fig. 193.1). In the intercostal spaces 

 lying in front of it the systolic sound originating in the right 

 ventricle may also be heard more clearly, and it is audible quite 

 distinctly in the right 3d-4th intercostal spaces (Fig. 194.1), the 

 transmitted and much attenuated murmur being also percep- 

 tible. The diastolic sound is clear, the second aortic sound 

 usually normal in strength, the second pulmonic sound (in the 

 left third intercostal space in the lower half of the lower third 

 of the chest [Fig; 193.3]) much increased, clear and short, i. e., 

 accentuated, because the blood column, which within the pul- 

 monary artery is under an increased pressure, is thrown with 

 greater force against the semilunar valves. The pulse presents 



