CARDIAC MICROPHONE

Some information about the functioning of the heart may be obtained using a simple stethoscope, listening to the heart sounds. These sounds correspond to the opening and closing times of the main valves but there are others which are not always perceptible. A much more comprehensive analysis of the heart sounds can be made using a phonocardiograph by which the heart sounds are presented as their original or modified waveforms on a high speed chart recorder. The microphone for this is usually a crystal microphone set back from the skin in a noise excluding housing, although contact types are also used. Normal heart sounds and murmurs occur in the frequency range 25-2000 Hz. Background noise and patient movement may create serious problems during phonocardiography. This may be overcome in the cardiac catheterization procedure by recording sounds from within the heart using a phonocatheter, or if miniature pressure transducers are mounted on the catheter, to record pressures within the chambers of the heart. These transducers may have sufficient frequency response to record the heart sounds as well.

Content and Design Copyright 2000 Dr. Malcolm C Brown.  See Title Page for more details