Origin and clinical relevance of musical murmurs

Abstract

Although our observations are limited to studies performed on a degenerated bioprosthetic valve that produced a musical murmur, we believe that they can be applied to musical murmurs caused by abnormal natural valves. Several points regarding the characteristics of musical murmurs have been clarified. A musical murmur results from a uniform periodic vibration of a cardiac structure. A non-musical murmur results from turbulent blood flow which initiates random vibrations of adjacent structures. The broad spectrum of frequency of a non-musical murmur reflects the broad range of random fluctuations of blood velocity that characterizes turbulent blood flow. The frequency, amplitude, and time of occurrence during systole or diastole of a musical murmur are dependent upon the hemodynamics in the vicinity of the vibrating structure. Variability of all of these characteristics of the murmur, therefore, may be expected. Musical murmurs may have a purer tone at a site distal to the source than close to the source. This may reflect a superimposition of a broad spectrum of noise due to turbulence close to the valve. With distance from the valve, turbulence attenuates more than the sound-pressure fluctuations which are due to the uniform vibrations of the valve. A pure tone, uncontaminated by this broad spectrum of noise due to turbulence, therefore, is heard at some distance from the valve.