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Doctors use stethoscopes to give themselves supersonic hearing. Your body makes sounds all the time, but most can't be heard with just your unaided ear.

If you've ever just finished running a mile or been very hungry, you'll know that you can hear your heart beating or your stomach growling respectively, just with your ears. These sounds never actually stop. A doctor uses a stethoscope as an amplifier. When placed against your body it picks up your internal sounds and makes them loud enough for us to hear.

The most common and diagnostically important sounds are from your heart, lungs, stomach, and upper elbow (to make blood pressure readings).

A normal heart makes two clicking sounds each beat as valves within shut at two different times each beat. Extra clicks and whooshing sounds suggest that valve system is no longer 'watertight' and is malfunctioning. We can detect flow problems, timing problems, and valve problems in your heart via a stethoscope. 

Your stomach is also a constant noise maker. This occurs as it pushes food and gas along creating gurgling sounds. If it starts to work harder as in gastroenteritis, it will make more noise, and if it stops working then it will make little to no noise as in a bowel obstruction.

Breathing is deceptively quiet to your naked ear but not with a stethoscope. The back and forth rush of air into and out of your chest is easily magnified by a stethoscope. We can hear bubbling and gurgling of excess fluid or sputum collection. We can hear narrowing of the bronchi as wheezes as in asthma. And the absence of sound can also be diagnostic. A lung field with  no air movement heard can signify catastrophic lung dysfunction such as a blood clot pulmonary embolism, air bubble pneumothorax, white out by pneumonia and other critical emergencies.  

Doctors learn to pick up what's wrong with you using stethoscopes by learning what sounds are normal, which are abnormal, and what they signify. Much of the pioneering work in this field was done by the inventor of the stethoscope, Dr. Rene Laennec, by listening to morbid patients before death and comparing his audio findings to the visual autopsy findings later. Sadly, he himself succumbed to pneumonia eventually and died from it but not before leaving us this enduring tool of medicine which has saved millions of people worldwide since.  

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