Aknowledge of blood flow pathways within the heart and great vessels is extremely useful in understanding the transmission patterns of cardiac murmurs. This is true because murmurs are maximally transmitted along the direction of flow of the jet or column of blood associated with their production. This observation is in keeping with the newer vortex-shedding theory of murmur genesis and less consistent with the older turbulence theory of murmur production (Fig 1).1-3
Turbulence represents a breakdown of laminar flow and is associated with random movement of fluid particles. Although turbulent flow regularly occurs in the cardiovascular system, the energy levels involved are rarely, if ever, capable of producing audible sound. Also, the turbulence theory fails to account for other characteristics of murmurs, such as their variation in pitch and intensity. Vortex shedding involves the formation of vortices or eddies which arise as a column of fluid passes an obstruction.