Auscultation in noise: A program to develop a stethoscope capable of functioning during aeromedical transport

U.S. Army helicopters used to provide aeromedical transport are extremely noisy (105 dB). This prevents auscultation with current stethoscopes. Ten subjects used four different stethoscopes in noise at 70–100 dB in order to determine the detection threshold of a body sound. The stethoscopes differed in performance (p=0.001); the best being the acoustic, followed by the three electronic stethoscopes. The threshold of noise for the detection of heart and breath sounds was 80 dB and 70–75 dB, respectively. A comparison of a standard stethoscope and one modified with Communications Ear Plugs revealed a difference (p=0.05) at 70 and 80 dB that disappeared at higher noise levels, implying that it was not simple masking, but that noise was amplified after entering the sensing head. Despite the poorer performance of the electronic stethoscopes, the need for a gain of 30–35 dB indicated that this was the preferred route for development. A sensor with an acoustic impedance match close to body tissue, but poorly mat...