How Doctors Listen: A sonic journey through the body

You're listening to 20,000 Hertz.

I'm Dallas Taylor.

A few years ago, I was locked into an anechoic chamber, which is one of the quietest places on Earth.

While I was inside, I could hear my heartbeat super clearly.

I could hear the blood rushing through my veins.

And I could hear my digestive system.

Sounds like these contain critical information about our health.

That's 20,000 Hertz producer Fran Board.

Today, there are all kinds of tools for capturing the sounds that our bodies make, but doctors have been listening to them for millennia.

If you look back at the ancient Greek world from 2,000 plus years ago, you see references to listening to the patient's body.

That's Dr.

David Steensmer.

He's an expert in blood cancers and disorders, and he's also a big medical history buff.

I'd always been quite interested in history as a way of understanding the present.

David says that Hippocrates, who's also known as the father of medicine, was really into sound.

It was clear even in the Hippocratic times that they would put their ears up to the chest wall or the belly of the patient and listen and certain sounds would suggest certain diagnoses.

For example, Hippocrates realized that if he shook patients by their shoulders and then listened to the sounds coming from their chest, he could tell whether they had any fluid buildup in there.

Of course, in past centuries, doctors had fewer medical tools to work with.

But there's one listening technique in medicine that doesn't require any special equipment.

It's called percussion.

It's the same sort of thing that you would use to try to find, say, a stud in a wall.

By tapping along the wall with your finger or with an instrument, you hear an echo until you get over the board underneath and then you hear a bit of dullness.

And there was a physician in the 18th century, Leopold Auenbrugger, who really brought this technique into medicine.

Auenbrugger was the son of an innkeeper.

When he was a boy, he'd watch his father try to work out how much wine was left in casks by knocking on them with his knuckles.

There would be a shift in the sound that would happen at the fluid level and he would know this one's full, this one's nearly empty, this one's in between.

Once Auenbrüger became a doctor in Vienna, he brought the tapping technique with him.

He started using this same percussion technique to measure fluid levels in patients.

For instance, if it was thought that perhaps the patient's left lung was surrounded by fluid or filled with fluid, Auenberger could percuss and he'd hear a dullness on the left, but an echo echo on the right.

That would help him diagnostically.

Auenbrügger's new listening technique took a while to catch on.

Back then, it was actually pretty rare for doctors to train via hands-on time with patients.

Most of their learning was done purely from books.

It was even common for doctors to diagnose people by letter without ever having met them.

He published this and it was really largely ignored until Napoleon's favorite physician, a guy named Jean-Nicolas Corvusar, who was really trying to rehabilitate physical diagnosis and move it into the modern era.

Corvisar was part of a larger movement in medicine that emphasized hands-on training and hospital internships.

So he came across Allen Brugger's writings and started to incorporate that in his own practice and teach it.

Eventually, the percussive technique became standard practice.

It's a technique that we still teach medical students in which there's still something being done in your local emergency room, probably right at this moment by a physician at the bedside.

Not long after Corvissa started bringing percussion to the masses, another French physician named René Laneck was busy working in Paris.

One day, a patient came into his office.

He was asked to see a patient who had symptoms that were suggestive of heart disease.

And normally the practice would be to put your ear to the chest wall and try to listen for heart sounds,

supplemented by percussion in the Allenberger style.

But in this case, Lanek was faced with two problems.

One was that she was quite obese, and so when he would have tried to listen, it would have been muffled by intervening layers of fat.

The other was that she was a young woman and society had evolved in a way that was considered indecorous to put your ear if you were a middle-aged male physician to the bosom of a young woman.

So he had to improvise.

Linneck thought, what could he do to try to hear this woman's heart and chest cavity better?

And he wrote later that he had seen some children playing a little game where one child would put their ear to a long wooden beam, and then the other would either talk into the beam

or make some scratches on the beam.

And the children noticed that the sound was conducted well by this wooden beam.

Lenick thought he might be able to do something similar with his patient.

So he rolled a few dozen sheets of paper into a tube,

placed one end on her chest, and listened through the other.

To his excitement, he could hear her heart really clearly, even better than he normally could.

Lenick knew he was onto something, but he wanted a tool that was hardier than paper.

And as it turns out, his hobby was the flute,

and he had carved some of his own flutes out of wood.

And so he made a very simple wooden tube that took the place of that choir of paper and used that as an intermediary between him and the patient's body.

This wooden tube was the first first true stethoscope.

That became very popular because other physicians quite quickly saw the benefit of it.

Over the next few hundred years, the stethoscope evolved into the tool we recognize today.

The wooden cylinder was replaced with two rubber tubes, one for each ear, and different attachments were developed for the end that goes on the patient.

The first stethoscope that I bought in medical school and took on loans to be able to purchase had a bell and a diaphragm that you could flip.

Today, this design is pretty common for a stethoscope.

The round metal piece usually has two sides to it.

One side is a concave bell and the other is a flat diaphragm.

The bell tends to be more useful for heart sounds, whereas the diaphragm can be more useful for certain types of murmurs and for listening to abdominal sounds because they tend to be higher pitched.

For such a relatively simple piece of equipment, the amount of information you can hear through a stethoscope is pretty amazing.

There's just so much you can hear about the heart.

The valves clicking,

murmurs if one of those valves doesn't open or shut properly.

You can hear whether the heartbeat is irregular.

You can hear certain echoes that happen when the heart is failing.

You can hear when the heart is rubbing inside the sac that it lives in, if there's inflammation in that sac.

But it's not just the heart.

There's also the lungs.

You can hear wheezes if somebody's airways are narrowed.

If the little air sacs, the alveoli, have fluid in them.

You can hear them actually crackle as they open.

It sounds just like somebody's stepping on one of those bubble wraps.

Doctors can also listen to blood vessels.

If somebody's had a stroke, you can listen and maybe you hear whistling.

That suggests turbulent blood flow in those arteries and that suggests the patient may have a narrowing.

They may have an atherosclerotic plaque there.

And then there's the abdominal region.

If you have somebody with a bowel obstruction and you put the stethoscope on the belly, you might hear very high-pitched noises, tinkles, as the bowel is trying to squeeze past the obstruction.

Or if the bowel is asleep, you might listen and hear no bowel sounds at all.

That often happens after a surgical procedure, and the surgeon will then listen to the belly a few times each day to hear, are the bowels waking up yet?

Can I advance the patient's diet a bit once I'm starting to hear noise?

Sometimes that noise is so loud that we can hear it outside.

Our stomach's rumbling, as we say, a phenomenon called borborygmy, which is a technical name for rumbling stomach.

So the next time your stomach's rumbling, you can casually tell people, pardon my borboryme.

As you can imagine, there's a lot of training that goes into deciphering this strange sonic language.

Right now, when you go to medical school and you're handed your stethoscope, you're trained to do two things.

That's Dr.

Daniel Weiss, a cardiac expert.

One of them is passive capture of the sounds.

Listen to the heartbeats, have the patient take a breath in and out, listen to the abdomen by putting the stethoscope on the stomach.

But that's not always enough.

The sounds can be confusing.

So sometimes we try to use physiology to help us with understanding the sounds.

And that's particularly important when there are sounds that sound similar to the ear, we call them acoustic sound-alikes, but in fact stem from different physiologic conditions.

This is why doctors often ask you to do different things while they listen through their stethoscope.

Take a deep breath and hold it.

Lie on your side, sit up, lie back.

All these are designed to make subtle changes in the physiology that will make the sound get louder, softer, whatever it is.

The stethoscope revolutionized medicine, and in popular culture, it's the quintessential medical accessory.

Studies show that people even trust doctors more when they're wearing one.

But today, the stethoscope is just one of an array of tools that doctors use for listening.

Some of these devices give doctors superhuman listening abilities, where the tiniest little sounds can be captured and analyzed.

These sounds can tell them all kinds of surprising things about their patients' health.

That's coming up after the break.

Doctors have been listening to the human body for thousands of years.

But even with the help of a stethoscope, these sounds can sometimes be quiet or hard to read.

Nowadays, the electronic stethoscope amplifies sounds to make them easier for doctors to hear.

A stethoscope that has an electronic amplifier built into it can really make even the most subtle murmurs loud and clear.

For many doctors, this innovation has been a huge upgrade.

When I was in my late 30s, I lost part of my hearing in my left ear.

And when my old medical school stethoscope finally wore out after 20-some years, I got an amplified one.

And I couldn't believe how much of a world that it opened up again for me.

In recent years, sound recording has also become an important part of medicine.

One of the beautiful things about audio as a tool is that it's cheap, it's easy to do at the bedside, it's reproducible as many times as you want.

Compare that to an imaging system like an x-ray or an MRI.

They're expensive, not everybody can get to them all the time, you're certainly not going to do them very frequently.

And most importantly, sonic tools are really precise.

There are imaging systems where in some circumstances they only get 8 or 12 frames per second, some up to 30 frames per second.

Sound can be recorded at 44,000 samples per second.

So the temporal accuracy you can get is incredible and there's a wealth of information that's available.

Another reason these medical listening devices can be so useful is that our hearing is far from perfect.

Our hearing is not with a flat frequency response.

We don't hear all sounds equally.

The best sounds we hear are in the 1,000 to 3,000 hertz range.

That's where babies cry and people talk.

However, our worst hearing is at the extremes, at the close to 20 hertz, which is the lowest we can hear, and close to 20,000 hertz, which is the highest.

But some sounds in the body exist in those high and low extremes.

Many, many of the interesting sounds are 400 hertz or less,

which is the worst part of our hearing.

So stethoscopes do a not bad job of getting those frequencies to our ears, but there's room for improvement.

And we believe that there's information buried in the higher frequencies as well, in the higher harmonics.

And if you're not capturing that with a stethoscope, you're never going to be able to see the patterns.

To augment our imperfect hearing, Daniel has helped companies develop next-level stethoscopes, which are specifically designed for different parts of the body.

So typically now, if you've had a physician listen to your carotid artery, he'll take a regular stethoscope, the same one that he uses to listen to your heart and lungs, and put it up against your neck.

The problem is, you won't always get all the sound that you need when you do that.

We developed a version of that stethoscope that kind of looks like a bent straw, so you can really get it into the space there and get a really good sound capture.

By improving the quality of the sound that's captured, doctors can learn new things about how the body functions.

Take swallowing, for example.

We typically swallow hundreds of times each day without even thinking about it.

But there's a lot more going on than we realize.

When we swallow, there's an enormously complex sequence of events physiologically that occur.

Your trachea, also known as your windpipe, and your food tract, your esophagus, share a common beginning, right?

The top part of your your throat and then they split so how does the body know to let air go down into lungs then food into the stomach they're not the other way around so the way that happens is there is a little flap that sits closed over the esophagus because most of the time you're breathing and not eating so air can go up and down and when you swallow as the food comes down that common pathway that little flap jumps over to block the trachea so that food won't go down there and instead it goes down the esophagus and then it jumps back.

While all this is going on, there are quite a few sounds generated.

There are five different stages that occur during the physiologic swallow.

People tried in the 70s, I believe it was, to listen to those sounds, but all they basically heard was a glorified gulp

because they didn't have the proper equipment or processing to be able to hear anything.

We were able to record and hear all five components clearly with our stethoscope.

And we noticed that if the first three sounds are present in their proper order, there is basically never a problem.

And if either one of the sounds is missing or they're out of order, then there almost always is a problem going on.

To compare, here's a swallow heard through a normal stethoscope.

And here's the swallow recorded using a specialized high-tech stethoscope.

See if you can pick out the five different stages.

Here it is even slower.

When Daniel and his colleagues were recording these swallows, it actually led to another discovery.

In the course of listening to swallow sounds, we realized that we needed a timing signal.

How do we know when the swallow is beginning?

And we realized that every time you swallow, and now you'll pay attention to it the next time you swallow, you'll hear a little click in your ear.

Go ahead and try this yourself.

The tough tough part is ignoring the sound coming from your throat and only focusing on that click in your ear.

When Daniel's team was studying swallowing, they wanted to use that little click to get their timings in sync, kind of like a clapperboard on a movie set.

Scene six, take one.

But how do I know that the click is the same in everybody and how do I know the timing doesn't change if somebody has a cold or something?

So we started listening to those click sounds and our ENT said, wait a minute, we noticed that sound quality changes when there are different kinds of disorders in the ear.

And so we developed a special ear microphone to listen for the clicks.

Forget the swallow and I were just listening to the clicks.

This microphone basically looks like an earbud.

Here's that ear click recorded using this new tool.

And again.

Daniel and his colleagues discovered that this click goes away if there's any kind of blockage in the tubes that connect your middle ear and your upper throat.

So here's something that nobody ever listened to.

You don't even realize you had the click going on in your ear.

So that's an example of a never used before sound that, hopefully when we finish, can now be used for making diagnoses.

These days, some stethoscopes go even further.

There are already stethoscope systems that have AI with FDA approved algorithms for making diagnoses.

These devices record sounds from the patient, analyze them using AI, and suggest a diagnosis.

For example, one of the companies has an AI that's FDA approved for pediatric murmurs.

The accuracy of the AI was 94%,

and an expert pediatric cardiologist is about 88%, or 89%.

In other words, AI is already beating the human experts in diagnosing this condition.

As AI gets integrated into more and more medical devices, it's important for doctors to be kept in the loop about how these systems work.

Doctors don't like black boxes.

So if you give a doctor a tool and said, almost like a tricorder on Star Trek and say, put this on the chest, it'll listen and it'll, you know, boop, boop, boop, and give you a result.

They don't necessarily want that.

They don't want to just put some data in, get spit out an answer, and I've got to go with it.

They want to understand what is that system doing, how is it making that decision, and has to make sense to them.

So the first thing we realize is that we want to be able to always present the sound both unprocessed

and then with processing

to help them hear the difference.

They want to understand along the way what's happening and they want to be part of that.

For doctors, there's always a delicate balance between diving into the latest cutting-edge technologies and remembering the important lessons from the past.

Medicine is always changing and there's always so much to learn.

I think being connected to that very old art, but in a contemporary, technologically sophisticated way was very appealing to me.

It felt like you were connected with these ancient physicians like Lanek, like Alan Brugger, like Hippocrates, who were trying to figure out what the problem was with the patient so that they could then alleviate that suffering.

So it is both an art and a science.

I think people are aware of the usefulness of computers in making diagnoses, of newer, fancier equipment that's better able to acquire data.

I think they're a little concerned about the human touch, the human aspect of medicine perhaps being lost.

I try to reassure them that that's never going to happen.

There's the art and there's the science of medicine.

And these are tools.

They're not meant to be replacements for doctors.

They're meant to be enhancements.

And that's what we're trying to do.

As powerful as these new tools are, the ones we're born with are still just as relevant.

When our children were young, one of our daughters developed a cough.

And my wife and I brought our little girl to the pediatrician.

And he was a lovely man and an old school diagnostician.

And he examined her.

And he said that he didn't think this cough was anything to worry about, that it would probably slowly disappear over the next few weeks.

And I asked him how he knew that.

And he said,

when you're a pediatrician, hearing coughs is like somebody who's a musician listening to an orchestra.

You can pick out the individual instruments and know which one is the clarinet

and which one is the oboe.

And he said, this particular cough that she has, I've heard it many times.

It's something that happens after they get a respiratory infection.

The infection is clear, but they still have the cough as almost a habit for a while, but eventually it'll extinguish.

And that's exactly what happens.

So not all sound-driven diagnosis is through an instrument.

Sometimes it's just using the instruments that are on the side of our heads.

20,000 Hertz is produced out of the sound design studios of DeFacto Sound.

Hear more at de facto sound.com.

This episode was written and produced by Fran Borde.

And Andrew Anderson.

It was story-edited by Casey Emmerling.

It was sound design and and mixed by Jesus Sarteaga and Joel Boyder.

Thanks to our guests, Dr.

David Steensma and Dr.

Daniel Weiss.

And thanks to Joseph Butera from Bon Jovi Acoustic Labs for his help on this episode.

To learn more about their work, just follow the links in the show notes.

I'm Dallas Taylor.

Thanks for listening.