While there are some acoustical benefits to the more expensive stethoscopes, there are many acceptable inexpensive stethoscopes. While there are many varieties of stethoscopes on the market, the differences in performance are often subtle and will vary with the individual using the stethoscope. The stethoscope is a relatively simple device consisting of a chest piece to collect the sound waves, tubing to transmit the sound, and earpieces to direct the waves into the examiner’s ears. By interpreting the intensity, pitch and quality of the sound heard upon auscultation, one can make inferences about the health and pathology of the underlying organs and tissues. However, when the acoustical properties of the tissues differ, such as air filled lung and muscular thoracic wall, much of the sound wave is reflected and sound intensity decreases. As an example, sounds produced by vibrations in the heart muscle and valves are readily transferred across the similar tissue of the chest wall. At interfaces with closely matched acoustical properties, there will be little attenuation of the sound wave. Reflection occurs at the interface of two media with different acoustical properties resulting in decreased intensity of the transmitted sound wave. Different media will dampen vibrations at different rates and over different frequencies. Dampening of the sound wave results in decreased amplitude and thus decreased sound intensity. The sound quality is determined by the complexity of the pressure wave.ĭifferent compressible media have different acoustical properties that affect the transmission of sound. The sound pitch is determined by the frequency (cycles per second or Hz) and the intensity or loudness is determined by the amplitude of the pressure waves. Sound is produced by vibrations in air or other compressible media that are transmitted as waves and provide the stimulus for the subjective sensation of hearing. In order to accomplish this goal, it is necessary to understand the basic principles of sound production and transmission. The goal of clinical auscultation is to relate the sounds heard to the underlying pathology of the tissues examined. Principles of Sound Production and Transmission Since then, the stethoscope has evolved into its current form and has become one of the most cost effective diagnostic instruments available to clinicians. It was not until the early 1800’s that the stethoscope was “discovered” by Rene Laennec (1781 to 1826) who used a rolled cylinder of paper to listen to a patient’s chest. Robert Hooke (1635 to 1703)Įarly auscultation was performed by placing one’s ear directly on the patient’s body. I have been able to hear very plainly the beating of a man’s heart… who knows, I say, but that it may be possible to discover the motions of the internal parts of bodies… by the sound they make. With each movement of the heart, when there is the delivery of a quantity of blood from the veins to the arteries, a pulse takes place and can be heard within the chest. You shall know by this that the chest contains water and not pus, if in applying the ear during a certain time on the side, you perceive a noise like that of boiling vinegar. There are several historical references to auscultation in medical literature. The intensity and character of breath sounds help determine the location and pathology of thoracic disease.Īuscultation, or listening to the sounds within the body, is a fundamental examination procedure in clinical medicine. Abnormal, or adventitious, sounds are classified as crackles, wheezes, stertor, and stridor. Normal breath sounds are classified as bronchial, bronchovesicular, and vesicular. The character of the sound that is heard at the surface is determined by the factors influencing the production of the sound, and acoustical characteristics of the intervening tissues. Breath sounds originate in the large airways due to turbulence in airflow. Differences in the acoustical density of tissues result in attenuation, reflection, and refraction of these sound waves. Auscultable sounds originate as mechanical vibrations within compressible media that are then transmitted through the tissues as sound waves. Differences in the intensity and character of sounds can be useful in distinguishing underlying thoracic pathology. Many clues as to both respiratory and cardiac function and disease can be obtained through proper auscultation. Thoracic auscultation and percussion are two of the most useful and economical procedures of a physical examination. Books & VINcyclopedia of Diseases (Formerly Associate).VINcyclopedia of Diseases (Formerly Associate).
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