Biophysics of Heart Sounds and Its Application to Clinical Auscultation

Much research has been carried out recently into the means by which heart sounds and murmurs reach the stethoscope from their point of origin. Heart sounds originate as vibrations of the cardiac valves and travel as transverse vibrations with low velocity over the walls of the ventricles and great vessels. Where these structures are in contact with the thoracic surface they emerge, at the `auscultatory areas', and spread like ripples over the chest surface. Murmurs originate in the cavities receiving the blood stream, and are loudest in the cavity that is less distensible. Frequency, damping in transit and the possible misinterpretation of apparent `splitting' seen in phonocardiographic records are discussed. This basic knowledge of modes of transmission allows the interpretation of unusual locations of auscultatory areas in disease states, and explains some puzzling findings obtained with microphones mounted on cardiac catheters.