The stethoscope is an acoustic medical device used for listening the internal sounds of the body. It can be used to listen to lung, heart, and intestines as well as blood flow in the arteries. With a sphygmomanometer it can be used to measure blood pressure. Along with listening to bodies a stethoscope might be employed to listen to automobiles to diagnose any damage as well as used to check scientific vacuum chambers for leaks. A phonendoscope is a stethoscope that intensifies sounds.

In 1816, Rene Laennec, of France, invented the stethoscope. It was composed of a monaural wooden tube. It was similar to an ear trumpet; in fact it was almost indistinguishable from the historical hearing aid device in structure and form. George Cammann perfected the binaural stethoscope design that Arthur Leared invented in 1851. Cammann’s design was the standard until the 1940′s when Rappaport and Sprague designed a new stethoscope. Their design used one side to measure respiratory system and the other is used for cardiovascular system. Hewlett-Packard made the Rappaport-Sprague design.

In the 1960′s Dr. David Littmann created a lighter stethoscope with improved acoustics.

Richard Deslauriers patented the first external noise reducing stethoscope, the DRG Puretone, in 1999. It reduced noise with two steel coils that dissipated outside noise to inaudible heat energy. However, due to the steel added into the stethoscope the weight of the instrument was causing neck strain. Marc Werblud created a lightweight noise canceling stethoscope which improved sound quality and reduced neck strain. Improvements since then have created even lighter weight stethoscopes as well as diaphragms which could be sanitarily changed for each patient.

The stethoscope works by transmission of sound from the chest piece through air-filled hollow tubes to the listener’s ears. There is a bell and a diaphragm on the stethoscope. The bell transmits low frequency sounds and the diaphragm transmits high frequency sounds. The 2-sided stethoscope, invented by Rappaport and Sprague, was created in the 20th century. The main problem with acoustic stethoscopes was that the sound was extremely low. In 1999 the stratified continuous lumen was invented. This solved the problem of the sound being to quiet. Acoustic stethoscope’s are now the most commonly used.

Electronic stethoscopes electronically amplify the sound in order to overcome the low sound problems. They convert acoustic sound waves to electric signals that can be amplified. Electronic stethoscopes can also be wireless, a recording device, provide noise reduction, signal enhancement, as well as both visual and audio output.


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