Acoustic coupler for acquisition of coronary artery murmurs

The aim of the study was to design and evaluate a coupler/ microphone system for recording weak murmurs from stenoses in the coronar artery. The suggested design is based on the use of a high quality microphone, coupled to the chest through a small air cavity. Since the determination of the exact frequency range of interest related to murmurs is part of the purpose of the study, one of the goals of the design was to achieve a high signal to noise ratio in a broad frequency range. The high cut off frequency of the coupler is determined by the acoustic impedance of the chest and the design of the coupler, while the low frequency behavior was determined by the properties of the microphone, electronic circuits and inadvertent leakages in the acoustical coupling. The requirement for the microphone and pr-amplifier was a low inherent noise level. The setup was used for collection of heart sounds in a clinical trial including 463 patients referred for elective coronary angiography. The preliminary results show, that it was possible to record heart sound in the diastolic period with a sound pressure level approximately 30 dB above the noise floor
of the microphone and recording system in the frequency range from 200-700 Hz. The capability of the sensor to record diastolic heart sound in the relevant frequency range indicates that the sensor is suitable for recording of coronary murmurs.