How Does a Stethoscope Work? A Complete Guide

Not only in the medical field, but everyone has known of a stethoscope at some point in their life. It is the most common thing used by every doctor and physician while examining his patient. But have you thought about how this tool works? What is the mechanism behind the stethoscope?

The diaphragm and the stethoscope tube amplify small sounds inside the human body, such as the sound of a patient’s heart, by increasing its volume. The Doctor listens to amplified sounds with stethoscopes that send their sounds up the ear tube to their ears.

It does not matter whether you are a medical student or not. You can use the stethoscope at home to check the sick person rather than going to the clinic. So for this purpose, all individuals need to know how to use a stethoscope to monitor patient health. 

My goal in this article is to explain to you how and why stethoscopes are used. 

How Does a stethoscope work? 

When a doctor examines or diagnoses a patient, he first listens to his body sounds. Thus, the stethoscope is a device that detects sound waves.    

Two rubber tubes lead from a disc called a chest piece to two earpieces. Placing the chest piece against the patient’s chest causes a vibration in the plastic disc (diaphragm). Thus, acoustic pressure produces pressure waves. 

These pressure waves by air travel up the hollow tubes to the doctor’s ears and make them able to hear the tiny sounds. 

Parts of the Stethoscope and How They Work:

Stethoscopes can be classified into two groups based on their uses: the acoustic stethoscope and the electronic stethoscope. However, the acoustic stethoscope is an essential and commonly used tool. 

Chest Piece:

There are two sides to a stethoscope: diaphragm and bell. This is the central part of the stethoscope, which you place on the patient body to capture sounds. A diaphragm is a flat, large part like a disc. Its work is to indicate the higher-pitched sounds, especially normal heartbeat sounds and murmurs. 

Moreover, the bell is a small metal piece you can use to identify low-pitched sounds, like lung sounds, blood vessels, and arteries. 

Tubing:

The name indicates a long plastic or rubber tube starting from the chest piece to the ear tips. It is the Y-shaped tube that transmits sound waves from the chest piece to the headset. They split into two parts as they near the headset so that the listener can hear it in both ears. 

Headset: 

There are metal tubes called binaural at the end of the rubber tube that carry the sound to the ear tips in the listener’s ears. In addition to being comfortable, rubber ear tips create a seal against external noises. As a result, it blocks out the ambient sound in the background. 

Tunable technology:

Some branded acoustic stethoscopes feature tunable technology, which is common in modern days. The tunable technology combines a bell and diaphragm on one side of the chest piece. It is possible to adjust the chest piece pressure to detect sound when it is placed on the patient. 

Moreover, modern stethoscopes also contain noise-canceling elements in the earpieces to reduce unwanted outside noise. There is also electronic equipment in the chest piece that records and outputs sound.

How Do Body Sounds Reach Our Eardrums?

The stethoscope diaphragm vibrates when placed on a patient’s chest because sound waves traveling through their body cause the diaphragm to vibrate. 

If the diaphragm were a separate device, vibrations would travel outward, but sound travels in a specific direction due to the tube attached to the diaphragm.

As waves travel through the rubber tube, they reflect off of its walls. Multiple reflections are the name of this method. Each wave, therefore, passes successively from the ear tips of the device to the eardrums of the listener.

Can a Stethoscope Hear Through Clothes?

If a doctor is using an electronic stethoscope, he can listen to the sounds even through clothes. But if someone is using a traditional acoustic stethoscope, he may make sure that not place a chest piece on the cloth. 

But he may ask the patient to slightly move the cloth and place the stethoscope directly against the patient’s skin for better acoustic sound. 

What Can Affect the Working Of A Stethoscope? 

Cleaning Is Important

Stethoscopes that are usually kept in pockets or do not remain clean may accumulate debris or dirt, which blocks the path for sound. Preventing this with routine care and maintenance is critical. 

Sealed Tubing:

Stethoscopes transmit body sounds through an airtight seal into the ear of the user. However, if the chest piece was damaged or cracked, an airtight seal might be compromised. 

Wearing an Improper Headset:

Incorrectly worn headsets can result in poor acoustic sealing or completely block out sound.

Hold the stethoscope headset up in front of your ear nodes, and make sure the ear tubes are pointing away from you before placing the ear tips in your ears. If you wear the ear tips in your ears, the ear tips should face forward.

As soon as you correctly insert the ear tips, you should check for comfort and ensure the acoustics are improving. If not, adjust the headset according to your preference. 

You Have Not Fitted the Ear Tips Properly:

If you want optimal acoustic performance, use ear tips that are appropriately sized and fit your ears. For example, the compression of the soft-sealing ear tip could lead to poor acoustic performance if the ear tip is too large for the user.  

If the ear tip is too small, this may also be the case. Therefore, the most optimal acoustic performance depends on finding the individual exact ear size.

The Two Sides of a Stethoscope: What Are They for?

The diaphragm and bell are the two sides of a stethoscope. 

Use of Diaphragm: 

Listening to high-pitched sounds requires the use of the diaphragm. Using the diaphragm, you can hear breath, normal heartbeats, murmurs, and artery sounds. In a given period, high-pitched sounds, such as breath and heartbeats, cause more pressure waves since they travel at a higher frequency.

Use of Bell:

There is a slight difference in the way the bell works. Rather than picking up direct vibrations from the artery, it picks up vibrations caused by the movement of the skin. By doing so, the bell is capable of picking up low-pitched sounds. 

The skin still vibrates when lower-pitched sounds travel outward, even though they may have a more challenging time vibrating the diaphragm.

What Types of Sounds Can A Stethoscope Detect?

Auscultation is a method of listening to the sounds of internal organs using a stethoscope, which is an acoustic medical device. For example, using a stethoscope, one can hear the sounds of the heart like murmurs, whistles, arteries, lungs, intestines, and blood flow. In addition, it is commonly used when one measures blood pressure. 

Moreover, there are two types of sounds, high-frequency sounds and low-frequency sounds. Stethoscope diaphragms detect high-frequency sounds. Using a bell, we can hear low-frequency sounds.  

Photo of author

Muhammad Bilal Qayyum

MBBS from Taishan Medical University and currently working in Bahawal Victoria Hospital. The blog is a great resource for both novices and experienced users when it comes to stethoscopes. As I studied and practiced, I evaluated various models on the market, which led me to become an expert in stethoscopes.

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