Differential stethoscope distinguishing pulse from body noise - by differential amplification of inputs from sepd. listening sites at which microphones are located

摘要

An electronic unit receives electrical signals from microphone elements (16,18) in respective acoustic heads and directs chosen acoustic signals via a tube to the earpieces (20). The two heads are imposed on widely sepd. parts of the body under examination, and their microphone outputs are applied to individual operational amplifiers (26,28) which are followed by gain adjustment potentiometers (36,40) and a differential amplifier (32). The component of the output difference signal representing body noise (e.g. respiration) is minimised by adjustment of the potentiometers (36,40), and the distinguishable difference between the two heartbeat signals is amplified (42) for driving an earphone or loudspeaker (44). The differential amplifier (32) is adjusted for min. output noise by means of a balancing potentiometer (46). The signals may be displayed on an oscilloscope connected to output jacks (48-50).