When Was the Stethoscope Invented?
The stethoscope was invented by a French doctor, René Théophile Hyacinthe Laënnec, in 1816. It consisted of a wooden tube and was monaural. Laennec invented the stethoscope because he was uncomfortable placing his ear on women’s chests to hear heart sounds. His stethoscope was a perforated wooden cylinder one foot long, and he got the idea for it from the sight of children scratching one end of a wooden beam with a pin and listening to the transmitted sound at the other end.
He put one end of the tube to his patient’s chest and listened to noises made by the heart and lungs. He also observed that a rolled notebook, placed between the patient’s chest and his ear, could amplify heart sounds without requiring physical contact. Laennec’s device was similar to the common ear trumpet, a historical form of hearing aid; indeed, his invention was almost indistinguishable in structure and function from the trumpet, which was commonly called a “microphone”.
Laennec called his device the “stethoscope” (stetho- + -scope, “chest scope”), and he called its use “mediate auscultation”, because it was auscultation with a tool intermediate between the patient’s body and the physician’s ear. (Today the word auscultation denotes all such listening, mediate or not.)
He gathered evidence of what these sounds meant by comparing the various noises heard in living patients with the type of disease seen after they died. In 1819 he published his findings in one of the great books of medicine De l’auscultation médiate, and the stethoscope soon came into general use.
Auscultation (listening to sounds within the body) is most commonly used in diagnosing diseases of the heart and lungs. Nowadays a stethoscope is generally binaural (for both ears) and has two flexible rubber tubes attaching the chest piece to spring connected metal tubes with ear pieces.
In listening it is often necessary to use, bell shaped, open-ended chest piece for low-pitched sounds, and a flat chest piece covered with a semi rigid disc or diaphragm for high pitched sounds. Many modern stethoscopes have both kinds of chest pieces, readily interchanged by turning a valve.
The first flexible stethoscope of any sort may have been a binaural instrument with articulated joints not very clearly described in 1829. In 1840, Golding Bird described a stethoscope he had been using with a flexible tube. Bird was the first to publish a description of such a stethoscope but he noted in his paper the prior existence of an earlier design (which he thought was of little utility) which he described as the snake ear trumpet. Bird’s stethoscope had a single earpiece.
In 1851, Irish physician Arthur Leared invented a binaural stethoscope, and in 1852 George Philip Cammann perfected the design of the stethoscope instrument (that used both ears) for commercial production, which has become the standard ever since. Cammann also wrote a major treatise on diagnosis by auscultation, which the refined binaural stethoscope made possible. By 1873, there were descriptions of a differential stethoscope that could connect to slightly different locations to create a slight stereo effect, though this did not become a standard tool in clinical practice.
Rappaport and Sprague designed a new stethoscope in the 1940s, which became the standard by which other stethoscopes are measured, consisting of two sides, one of which is used for the respiratory system, the other for the cardiovascular system. Several other minor refinements were made to stethoscopes, until in the early 1960s David Littmann, a Harvard Medical School professor, created a new stethoscope that was lighter than previous models and had improved acoustics.
In the late 1970s, 3M-Littmann introduced the tunable diaphragm: a very hard (G-10) glass-epoxy resin diaphragm member with an overmolded silicone flexible acoustic surround which permitted increased excursion of the diaphragm member in a “z”-axis with respect to the plane of the sound collecting area.
In 1999, Richard Deslauriers patented the first external noise reducing stethoscope, the DRG Puretone. It featured two parallel lumens containing two steel coils which dissipated infiltrating noise as inaudible heat energy. The steel coil “insulation” added .30 lb to each stethoscope. In 2005, DRG’s diagnostics division was acquired by TRIMLINE Medical Products.
In 2015, Dr. Tarek Loubani announced an open-source 3D-printed stethoscope based on the 1960s-era Littmann Cardiology 3 stethoscope, which is out of patent. The 3D-printed equivalent is nearly an order of magnitude more affordable than the aforementioned non-3D-printed stethoscope and is intended to make the medical device more accessible to obtain, particularly in developing countries.