On the Unitary Nature of Cardiac Vibrations

Present day sensors are able to pick up both the low frequency pulsations (apex cardiogram or pressure tracing) and the high frequency vibrations (phonocardiogram). Studies were made by external tracings in 10 normal subjects and by both external and left ventricular catheterization tracings in 5 normal, anesthetized dogs. Either filtration or differentiation of the apex cardiogram results in a high frequency tracing, identical to a simultaneously recorded phonocardiogram. Either filtration or differentiation of the left ventricular pressure tracing results in a high frequency tracing, identical to a simultaneously recorded phonocardiogram. This demonstrates that high frequency vibrations of sonic frequency are produced within the heart by rapidly changing intracardiac pressures. These vibrations are then transmitted from the internal cardiac structures to the chest surface with minor apparent alteration. The low frequency (infrasonic) vibrations recorded on the chest wall apparently result from volume changes, movements of the heart, and rapid pressure changes.