A stethoscope is a medical device with which it becomes possible to conduct auscultation, that is, listening to sounds that are present in the heart, blood vessels, lungs, intestines, bronchi and other internal organs of a person. The most well-known areas of application of this device are listening to Korotkoff sounds in the process of measuring blood pressure, as well as determining the location of the probe inside the stomach during gastric lavage or enteral nutrition.
The head, which must be applied to the surface of the human body in the place necessary for listening, and which has the ability to capture various sounds from the organs, serves as the working part of the stethoscope. Other parts of the device are flexible sound-conducting tubes, through which sound enters the doctor’s auditory canals for analysis.
There are also non-medical models of stethoscopes, the purpose of which lies in the technical diagnostics of the functioning of various mechanisms – the crank mechanism, bushings, assemblies and parts. In a technical stethoscope, the sensitivity of the device is given by a thin metal rod, which is leaned against the place of study.
History of occurrence
Back in 1816, the French physician Rene Laennec, who is the progenitor of the diagnostic auscultation technique and the entire scientific method of diagnosis, invented the first stethoscope. In those days, to listen to the internal organs of patients, it was customary to put the ear to their body, which the innovator categorically did not want to do, therefore he used folded paper for this purpose, which perfectly conducted the sound, making it even clearer than when listening directly with the help of ear attachment. Since that time, the stethoscope has been modified and improved, but the principle of its operation and physical characteristics have remained the same.
In 1894, an improved stethoscope was proposed to be called a phonendoscope by professors of physics and preparatory clinical medicine A. Bianshi and G. Buzzi. The stethoscope acquired its modern look in the 1940s, when Sprague and Rappoport improved it, creating a new example of a standard for this device. Today it is called in the scientific community – the Sprague-Rappoport stethoscope.
A modern device called a stethophonendoscope helped to combine a stethoscope funnel and a phonendoscope membrane in the design of a two-sided head. The term “stethoscope” today refers to both a phonendoscope and a stethophonendoscope.
The design of stethoscopes
The design of a modern stethoscope necessarily contains:
- head;
- membrane and funnel;
- sound pipeline;
- brackets;
- olives.
The head of the stethoscope is the part that must be applied directly to the patient’s body in order to capture and amplify auscultatory sounds from the organ under study. Heads are double and single sided. On one-sided heads, either funnels or membranes are located (in most cases). On bilateral, on both sides of the head, there is both, or on both sides of the head there are membranes of different diameters. With double-sided heads, to switch them, it is enough to turn the fitting 180 degrees, which is structurally connected to the sound duct.
To capture high-frequency auscultatory sounds, it is more rational to use a membrane, which is more sensitive in this case, and a funnel is better suited for low-frequency sounds. The membrane is understood as a flat or slightly convex outward, by analogy with the glass of a wristwatch, a plate mounted on the head of a stethoscope. Usually it can be changed over time or, if necessary, easily changed. Epoxy membranes reinforced with glass fiber material are supersensitive, while polyvinyl chloride membranes are less sensitive.
The sound duct is a flexible elastic hose with which sound is conducted from the head of the device to the hearing aid (in other words, ears) of a specialist. Sometimes the head is connected to one, and sometimes to two sound ducts. But even in the case of a single sound duct in front of the arms, it is necessarily divided into 2 parts.
The arms of a stethoscope are a pair of metal tubes that are connected to a sound duct. The springs of the temples provide a tight fit of the olives to the auricles. The tips of the temples can be positioned forward so that the olives can be inserted into the ears at an angle to the ear canals.
Finally, olives refer to two rounded tips with hard or soft texture temples that provide a comfortable fit of the stethoscope in the external auditory canal of the examiner using the device. Olives differ in size, they must be individually selected in accordance with the size of their own auditory canals. Olives, as well as membranes, can be easily replaced in the structure of this device with new or more comfortable ones. Ideally, the olives fit snugly around the practitioner’s ears, neither pressing too hard nor falling out of them. Thus, the closedness of the sound duct system is ensured, which avoids the appearance of an empty space between the olive and the ear and ensures a high quality of auscultation.
Types of instrument
The stethoscope can be subdivided in medical practice according to the categories of patients for which it is used in the practice of physicians. Thus, a therapeutic stethoscope is designed to listen to adult patients, a neonatal stethoscope – newborn babies under the age of 28 days, and a pediatric stethoscope is used to auscultate pediatric patients. The last 2 types of the device differ from the therapeutic one in the smaller size of the listening head.
In the practice of doctors, the Rappaport stethoscope is widely used, which is distinguished by its versatility with respect to patients of any age. Its distinguishing feature is a massive double-sided head, on which it is possible to install different nozzles – 3 types of funnels and 2 types of membranes, as well as equipment with two independent sound ducts to ensure sound transmission quality. The only disadvantage of this device is its large weight.
Also, stethoscopes are divided into types, depending on the specifics of the work of a specialist. Cardiac stethoscopes are distinguished by increased acoustic characteristics, which provides a much larger sound spectrum when listening to heart sounds. A fetoscope or Pinard stethoscope is used in gynecology to listen to the heart sounds of the fetus during pregnancy. It is most similar in design to the first devices that were invented 2 centuries ago. This is a stethoscope in the form of a rigid tube with a two-ended bell. When measuring blood pressure in patients, a simple device is used, equipped with a single head with a membrane.
In modern medical practice, an electronic stethoscope is widely used today, containing a microphone in its head, which is capable of converting the sounds perceived by the device into an electronic signal to be processed and output to speakers that are built into the olives of the device. It can be used to perform auscultation with double conversion of the received sound in the adult category of patients.