Symposium on Cardiovascular Sound

CADIOVASCULAR sound may be divided into 2 categories,' namely, murmurs that result from turbulence in streams of blood flowing so rapidly that the critical Reynolds2' 3 number is exceeded and, heart sounds that represent vibrations resulting from abrupt changes in the velocity of blood movement. Since closure of the heart valves suddenly arrests or reverses the movement of blood, normal valve function undoubtedly coiitributes to the production of heart sounds. This discussion is limited to the structure and function of the atrioventricular valves, since I have not studied the semilunar valves directly. Each atrioventricular valve consists of 2 broad cusps attached at opposite sides of a large oval opening. Chordae tendineae enter the structure of the valve cusps at or near their edges to prevent eversion of the cusps when ventricular pressure is high (fig. 1). The chordae tendineae of the mitral valve insert primarily into 2 papillary muscles.46The tricuspid valve is supported by chordae tendineae from 3 papillary muscles inserting into 2 main cusps and a large intermediary cusp. Thus, the structure and function of the 2 atrioventricular valves are sufficiently similar that only the mitral valve will be considered in detail. According to traditional concepts, an advancing gush of blood thrusts the atrioventricular valves widely open during early ventricular diastole. They are believed to be partially closed after atrial systole and clamped shut by a