Transmission of lung sounds through light clothing

Doctors are exhorted to always place the stethoscope directly on the skin and never to auscultate through clothing. Nevertheless, casual observation reveals that doctors and even pulmonologists often violate this principle.

This study was designed to evaluate the sensitivity of two common stethoscopes when used through clothing.

Littmann Classic and Littmann Master Cardiology stethoscopes were studied under conditions of light (60-100 g), medium (240 g) and heavy (555 g) force when placed on a lung sound test platform with one or two layers of cloth (T-shirt material and flannel) interposed between the stethoscope and the test surface. The test platform was designed to mimic the acoustic and mechanical properties of the chest wall and was driven by amplified white noise. The recorded amplitude spectra were compared over a range of 150-1,000 Hz.

Compared to the sensitivity on a bare test platform surface, either fabric in single or double layers attenuated the sounds by a mean of 5-18 dB under light pressure. This attenuation was nearly abolished by the addition of either medium or heavy force on the stethoscope head.

The deleterious effect of one or two layers of indoor clothing on lung sounds acquired through a stethoscope can be negated by force on the stethoscope head making effective auscultation possible. Nevertheless, auscultation through clothing remains problematic due to the hindrance to inspection and percussion and the risk of acoustic artifacts caused by clothing.