The acoustic stethoscope is used in human medicine to listen to and auscultate various body sounds. Typically, these are heart sounds, sounds in the lungs and bronchi during inhalation and exhalation, bowel sounds caused by peristalsis, and possibly flow sounds in certain veins (e.g., the carotid arteries). Listening is done non-invasively, and the stethoscope is completely self-sufficient, i.e., independent of any power or other energy sources.
What is a stethoscope?
The acoustic stethoscope is a non-invasive diagnostic device designed to make certain body sounds more audible. The acoustic stethoscope is a non-invasive diagnostic device for making certain body sounds more audible. The word stethoscope is composed of the two ancient Greek words stethos and skopos and means “chest monitor”. A stethoscope usually consists of a head with a diameter of 30 to 46 mm, an attached tube and an earpiece to which the two branched ends of the sound tube are connected. The head serves to collect the structure-borne sound like an inverted bell and transmits the sound to the ends of the earhook via the sound tube. The head usually contains a membrane on one side, which is set into vibration by the incoming sound waves in a similar way to an eardrum and passes them on to the air in the sound tube. There are also models where the head can be used on both sides. Usually, one side of the head has a diaphragm and the other side is diaphragmless. The membraneless side is better suited for auscultation of low-pitched sounds, which is particularly advantageous for listening to heart sounds. The mode of action of an acoustic stethoscope is based on simple physical-acoustic laws.
Function, effect, and goals in diagnostics
One of the main applications of the stethoscope is in auscultation of heart murmurs and heart sounds. For all four heart valves, there are points near the sternum that, as points of contact for the stethoscope, allow the experienced physician to draw conclusions about the function of the corresponding heart valve. To the right of the sternum (to the left of the sternum as seen by the patient) are the two points for auscultation of the mitral and aortic valves as well as the so-called Erb’s point, which is suitable for acoustically diagnosing aortic insufficiency and/or mitral valve stenosis. To the left of the sternum (right of the sternum from the patient’s point of view) are the two points for listening to the tricuspid valve and the aortic valve. In addition to providing information about the quality of valve function, auscultation of heart sounds can also detect an atrial septal defect (ASD), a hole in the septum between the two atria, and the possible presence of myocarditis, an inflammation of the heart muscle. Diagnoses made on the basis of auscultation of the heart may require verification by further diagnostic procedures such as ECG and ultrasound examinations. Ultrasound examinations of the heart are particularly informative when performed esophageally, through the esophagus. The auscultated breath sounds also provide the experienced physician with important information about the presence of certain diseases or certain malfunctions within the respiratory system. The physician needs a certain amount of experience to be able to distinguish normal breath sounds from abnormal or pathological breath sounds and, above all, to be able to make an accurate diagnosis from perceived pathological breath sounds. A normal breath sound is produced by turbulent airflow in the trachea and bronchi (central breath sound). In addition, there are breath sounds that are muffled by lung tissue and chest wall and are often mistakenly referred to as peripheral breath sounds. Abnormal breath sounds may, for example, be too soft or too loud due to their origin or due to disturbed sound conduction, such as due to an accumulation of fluid (pleural effusion). Breath sounds such as typical rales are mainly caused by fluids or secretions in the airways and require further clarification after auscultation diagnosis. Another area of application for auscultation using a stethoscope is the two carotid arteries, the common carotid artery and the internal carotid artery, which may be affected by a pathological narrowing, a stenosis.The stenosis is usually caused by arteriosclerosis. Especially if the stenosis forms at the bifurcation of the two carotids – as is often the case – the typical flow sounds can be diagnosed with great certainty using a stethoscope, so that an impending stroke can possibly be averted. Auscultation of the upper abdomen can provide conclusions about disturbed intestinal peristalsis. Normally, bowel sounds should be heard about every 10 seconds. Constant loud sounds or the absence of any bowel sounds for several minutes indicate potentially serious disorders that need to be clarified immediately with other diagnostic procedures.
Risks, side effects, and hazards associated with diagnostic procedures
The use of the acoustic stethoscope to auscultate certain bodily functions is noninvasive and free of chemical or other stress to the body, and thus completely free of risks and side effects. A hypothetical risk may be that an inexperienced physician may make a misdiagnosis and initiate the “wrong” therapy based on the misdiagnosis made. However, auscultation of the airways may fail to detect interstitial pneumonia, which initially “only” affects the supporting connective tissue between the alveoli, because the breath sounds are normal. Meanwhile, more advanced acoustic stethoscopes are also available, which work with electronic algorithms. Interfering sounds are attenuated and the sounds that are important for diagnosis are amplified. The auscultated tones and sounds can be stored on a PC and are therefore reproducible. However, these “high tech” stethoscopes seem to be very slow to catch on, possibly because of the high price or because of (still) inadequate algorithms or because they are more complicated to use.
