PHONOCARDIOGRAPH

Typical Number in Hospital: 2

Cost Bands: 4,5

References: 3,9

The main sounds heard through a stethoscope placed over the heart are the noises made as the valves open and close. The first sound is low pitched, being associated with the closure of the atrio-ventricular valves and the second sound is of a higher pitch deriving from the closure of aortic and pulmonary valves. Other sounds (murmurs) indicate abnormalities.

The phonocardiograph consists of a microphone placed in a low-noise housing on the chest above the heart. The heart sounds so detected are normally split into three frequency bands and then displayed on a high speed recorder (e.g. ultraviolet, photographic, fibre-optic, or ink jet). Diagnosis of some heart conditions can be made from a review of the phonocardiograph records having regard to the size and frequency content of the sounds, but most importantly the presence of sounds other than the main two.

The phonocardiograph is usually used in conjunction with other signals including the ECG, carotid arterial pulse, and apexcardiogram. It is sometimes used in conjunction with an echocardiograph so that the movement of the walls of the heart and valve leaflets can be represented on the same chart as the echocardiograph.

For diagnostic echocardiography, background noise can be a serious problem. The sounds are sometimes detected using a microphone mounted on a catheter passed up into the heart as part of the cardiac catheterization procedure.