The stethoscope (Greek στηθοσκόπιο, of στήθος, stéthos - chest and σκοπή, skopé - examination) is an acoustic medical device for Auscultation, i.e. listening to internal sounds in the human body. It is most often used to listen to Heart sounds and breathing, though it is also used to listen to intestines and blood flow in arteries and veins.
Stethoscopes are often considered as a symbol of the doctor's profession, as doctors are often seen or depicted with a stethoscope hanging around their neck.
Stethoscopes are also used by mechanics to isolate sounds of a particular moving engine part for diagnosis.
Acoustic stethoscopes are familiar to most people, and operate on the transmission of sound from the chestpiece, via air-filled hollow tubes, to the listener's ears. The chestpiece usually consists of two sides that can be placed against the patient for sensing sound - a diaphragm (plastic disc) or bell (hollow cup). If the diaphragm is placed on the patient, body sounds vibrate the diaphragm, creating acoustic pressure waves which travel up the tubing to the listener's ears. If the bell is placed on the patient, the vibrations of the skin directly produce acoustic pressure waves traveling up to the listener's ears. The bell transmits low frequency sounds, while the diaphragm transmits higher frequency sounds. This 2-sided stethoscope was invented by Rappaport and Sprague in the early part of the 20th century. The problem with acoustic stethoscopes is that the sound level is extremely low, making diagnosis difficult.
Electronic stethoscopes overcome the low sound levels by amplifiying body sounds. Currently, a number of companies offer electronic stethoscopes, and it can be expected that within a few years, the electronic stethoscope will have eclipsed acoustic devices.
Rales are clicking, rattling, or crackling noises heard in the lungs on inhalation. Rales generally indicate the presence of fluid in the alveoli, and are often indicative of pneumonia.