Friedreich maintains that the augmented tension in the venous system causes an increased resistance in the systemic arteries, which leads to left ventricular hypertrophy.
ETIOLOGY.—Mitral regurgitation may occur at any age; it is especially liable to follow rheumatic endocarditis in the young.
Acute exudative and interstitial endocarditis of rheumatic origin is the primary cause of most of the changes which lead to mitral insufficiency. These changes cause the extensive retractions and thickenings which are present in most cases.
It may occur in conditions of extreme anæmia or where there is degeneration of the walls of the left ventricle.
It is not infrequently secondary to changes at the aortic orifice, produced either by an extension of endocarditis from the aortic to the mitral valves and their appendages, or by the secondary mitral valvulitis excited by regurgitant blood-currents from the aorta.
Mitral insufficiency may also be the result of the enlargement of the left auriculo-ventricular orifice which accompanies excessive dilatation of the left ventricle.
Disease of the columnæ carneæ and chordæ tendineæ, when their structures are so weakened as to allow the flaps of the valve to pass back of the plane of the orifice, will also cause mitral insufficiency.
Ulcerative endocarditis may cause it, either by perforation and rupture of the valves or by rupture of the chordæ tendineæ.
SYMPTOMS.—During the early stage of mitral insufficiency, when the hypertrophy of the right ventricle compensates for the regurgitation, there are no rational symptoms which would lead one to suspect its existence; but when the right ventricle is unable to overcome the obstruction to the pulmonary circulation caused by the regurgitant blood-current, there will be more or less dyspnoea, accompanied by a short, hacking cough, with an abundant expectoration of frothy serum. Sometimes the watery expectoration is blood-stained.
Frequently, the blood-stained expectoration is accompanied by free hæmoptysis, although it should be remembered that profuse hæmoptysis is far more frequent with stenosis than with regurgitation at the mitral orifice. But a cough and watery expectoration with occasional dark blood-stains are usually present as an advanced symptom of mitral regurgitation. Active physical exertion increases the dyspnoea and causes cardiac palpitation.