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The principle of a stethoscope

It usually consists of an auscultation head, sound guide tube, and ear hook. Perform (frequency) non-linear amplification of the collected sound.

The principle of the stethoscope is that the vibration transmission between substances participates in the aluminum film in the stethoscope, and the air alone changes the frequency and wavelength of the sound, reaching the “comfortable” range of the human ear, and at the same time shielding other sounds and “hearing” more clear. The reason why people hear sound is that the so-called “sound” refers to the mutual vibration of substances, such as the air vibrating the tympanic membrane in the human ear, which is converted into brain currents, and people can “hear” the sound. The vibration frequency that human ears can feel is 20-20KHZ.

There is another standard for human perception of sound, which is volume, which is related to wavelength. The intensity range of normal human hearing is 0dB-140dB. In other words: the sound in the audio range is too loud and weak to hear, and the audio in the volume range is too small (low frequency waves) or too large (high frequency waves) to hear.

The sound that people can hear is also related to the environment. The human ear has a shielding effect, that is, strong sounds can cover weak sounds. The sound inside the human body, such as heartbeat, bowel sounds, wet rales, etc., and even the sound of blood flow is not very “heard” because the audio is too low or the volume is too low, or it is obscured by the noisy environment.

During cardiac auscultation, the membrane earpiece can listen to high-frequency sounds well, and the cup-type earpiece is suitable for listening to low-frequency sounds or murmurs. Modern stethoscopes are all double-sided stethoscopes. There are both membrane and cup types on the auscultation head. The conversion between the two only needs to be rotated by 180°. Experts suggest that clinical doctors should use double-sided stethoscopes. There is another patented technology called floating membrane technology. The membrane auscultation head can be changed into a cup-type ear head in a special way to listen to low-frequency noise. Both normal and abnormal lung sounds are high-frequency sounds, and only a membrane ear can be used for lung auscultation.

Types of stethoscopes

Acoustic stethoscope

Acoustic stethoscope is the earliest stethoscope, and it is also a medical diagnostic tool familiar to most people. This kind of stethoscope is a symbol of the doctor, and the doctor wears it on the neck every day. Acoustic stethoscopes are the most commonly used.

Electronic stethoscope

The electronic stethoscope uses electronic technology to amplify the sound of the body and overcomes the high noise bug of the acoustic stethoscope. The electronic stethoscope needs to convert the electrical signal of the sound to the sound wave, which is then amplified and processed to get the best listening. Compared with acoustic stethoscopes, they are all based on the same physical principles. The electronic stethoscope can also be used with the computer-assisted auscultation plan to analyze the recorded heart sound pathology or innocent heart murmurs.

Photographing stethoscope

Some electronic stethoscopes are equipped with a direct audio output, which can be used to connect to an external recording device, such as a laptop or MP3 recorder. Save these sounds and listen to the previously recorded sounds through the stethoscope headset. The doctor can do more in-depth research and even remote diagnosis.

Fetal Stethoscope

In fact, the fetal stethoscope or fetal scope is also a kind of acoustic stethoscope, but it surpasses the ordinary acoustic stethoscope. The fetal stethoscope can hear the voice of the fetus in the belly of a pregnant woman. It is very beneficial for nursing care during pregnancy.

Doppler stethoscope

A Doppler stethoscope is an electronic device that measures the Doppler effect of the reflected waves of ultrasonic waves from body organs. The movement is detected as the frequency change due to the Doppler effect, reflecting the wave. Therefore, the Doppler stethoscope is particularly suitable for handling moving objects, such as a beating heart.