Auscultation of the Heart - III

Abstract

The essential difference between a sound and a murmur is that the former is due to sudden alteration in the speed of blood flow whereas a murmur results from turbulence developing in the blood stream. A murmur is usually of longer duration and of higher frequency than a sound. The principal factors which influence turbulence are the velocity of flow, the density and viscosity of the blood and the diameter of the vessel. Another important factor is that a narrowed orifice, as from valvular stenosis, will give rise to eddies beyond the obstruction. A similar effect is produced by a relatively narrow vessel opening into a wider one as in dilatation of the first part of the aorta or pulmonary artery.

Murmurs may be heard in systole or diastole or may appear to be continuous throughout systole and diastole.

Diastolic and continuous murmurs are always due to organic disease but a systolic murmur may be present not only without any functional disability but without any clinical, radiographic or electrocardiographic evidence of organic heart disease.