Acoustics of Electronic Stethoscopes for Health Professionals

Commercially available electronic stethoscopes for auscultation often report amplification levels and may or may not publish amplitude-frequency (spectral) response curves. Additional data may be helpful to consumers who use stethoscopes in less-than-ideal listening environments or have hearing loss. The purpose of this research was to describe our method for evaluating electronic stethoscopes relative to a nonelectronic stethoscope.

One nonelectronic and eight electronic stethoscopes at maximum volume with their bell and diaphragm modes were acoustically evaluated using digitized heart and breath sounds, a stethoscope speaker pad, and an industry-standard manikin ear simulator. Some electronic stethoscopes had wireless connectivity to wearable Bluetooth earbuds, and these were evaluated also. For each stethoscope, output measurements of digitized heart and breath sounds were recorded in a quiet room. For direct comparisons, measurements were categorized by expected spectra into heart (bell) sounds (~20-500 Hz) and breath (diaphragm) sounds (~100-1000 Hz).

Relative to published human threshold tone and 1/3-octave band data, as well as nonelectronic stethoscope output, all electronic stethoscopes clearly demonstrated some measure of amplification across the amplitude-frequency (spectral) range for digitized normal heart and breath sounds. Differences observed may be specific to bell versus diaphragm modes, acoustical tubing (or lack thereof), wired versus wireless modes, models within the same make, and use of active noise cancellation, to name a few. Importantly, manufacturer-reported amplification values (e.g., "×" specifications) did not reliably reflect frequency-specific acoustic output within clinically relevant heart and breath sound regions.

The methodology described to analyze stethoscope outputs appears to be an effective starting point for evaluating various characteristics of stethoscopes with a lens toward assisting health professionals and students working in less-than-ideal listening situations or for those with hearing loss. While all electronic stethoscopes evaluated offered amplification, there was great variability in amplitude-frequency responses, which may help inform stethoscope selection based on listening needs, various listening environments, and/or degree and configuration of hearing loss.