The sounds our bodies make can tell doctors all kinds of surprising things about our health. In this episode, we unpack the history of sound in medical diagnosis, from Hippocratic times, to the invention of the stethoscope, to the specialized tools and AI systems used today. Along the way, we’ll hear detailed recordings of these medical sounds, and learn what each of them means. Featuring Dr. David Steensma and Dr. Daniel Weiss.

MUSIC FEATURED IN THIS EPISODE

Architect - Palladian
Eltham House - Tall Harvey
Eltham House - Cherry House
Eltham House - Sudden Courier
The Caravan - Tools and Practices
Architect - Hedgeliner
Eltham House - The Griffiths
Eltham House - Leatherbound
Migration - Gusty Hollow
Resolute - Building the Sled
Bitters - Lover’s Hollow

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View Transcript ▶︎

You’re listening to Twenty Thousand Hertz. I’m Dallas Taylor.

[music in]

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… [SFX] I could hear the blood rushing through my veins… [SFX] And I could hear my digestive system…

[SFX + music out]

Fran: Sounds like these contain critical information about our health.

That's Twenty Thousand Hertz producer Fran Board.

Fran: Today, there are all kinds of tools for capturing the sounds that our bodies make. But doctors have been listening to them for millenia.

[music in]

David Steensma: 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.

Fran: That’s Dr. David Steensma. He’s an expert in blood cancers and disorders, and he’s also a big medical history buff.

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

Fran: David says that Hippocrates, who’s also known as the Father of Medicine, was really into sound.

David Steensma: 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.

Fran: 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 build-up in there.

[music out into SFX]

Fran: 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.

David Steensma: 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 [SFX - tapping echo] until you get over the board underneath, and then you hear a bit of dullness. [SFX - tapping dull]

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

[music in]

Fran: 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.

David Steensma: There would be a shift in the sound that would happen at the fluid level, and he would know this one's full… [SFX - tap, tap] This one's nearly empty… [SFX - tap, tap] This one's in between… [SFX - tap, tap]

Fran: Once Auenbrugger became a doctor in Vienna, he brought the tapping technique with him.

David Steensma: 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, Auenbrugger could percuss and he'd hear a dullness on the left [SFX - dull taps] but an echo on the right, [SFX - echoey taps] that would help him diagnostically.

[music out]

Fran: Auenbrugger'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.

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

Fran: Corvisart was part of a larger movement in medicine that emphasized hands-on training, and hospital internships.

David Steensma: So he came across Auenbrugger’s writings and started to incorporate that in his own practice and teach it.

Fran: Eventually, the percussive technique became standard practice.

David Steensma: It's a technique that we still teach medical students, and which is still something being done in your local emergency room, probably right at this moment by a physician at the bedside. [sfx - dull tap]

[music in]

Fran: Not long after Corvisart started bringing percussion to the masses, another French physician named René Laennec was busy working in Paris. One day, a patient came into his office.

David Steensma: 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 [sfx: heartbeat], supplemented by percussion in the Auenbrugger style. [sfx: echoey chest taps]

Fran: But in this case, Laennec was faced with two problems.

David Steensma: 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.

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

Fran: So, he had to improvise.

David Steensma: Laennec 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 [sfx: French child talking through wood] or make some scratches on the beam. [SFX - scratches through wood] And the children noticed that the sound was conducted well by this wooden beam.

[music out]

Fran: Laennec thought he might be able to do something similar with his patient. So he rolled a few dozen sheets of paper into a tube, [SFX: paper sounds] placed one end on her chest, and listened through the other.

[music sneaks in]

[heartbeat into downbeat]

Fran: To his excitement, he could hear her heart really clearly, even better than he normally could. Laennec knew that he was onto something, but he wanted a tool that was hardier than paper. And as it turns out...

David Steensma: 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 quire of paper and used that as an intermediary between him and the patient's body.

Fran: This wooden tube was the first true stethoscope.

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

[music out]

Fran: 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.

David Steensma: 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.

Fran: 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.

David Steensma: 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.

[music in]

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

David Steensma: There's just so much you can hear about the heart. The valves clicking, [SFX] murmurs, if one of those valves doesn't open or shut properly. [SFX] You can hear whether the heartbeat is irregular, [SFX] you can hear certain echoes that happen when the heart is failing. [SFX] You can hear when the heart is rubbing inside the sac that it lives in, if there's inflammation in that sac. [SFX]

Fran: But it's not just the heart. There's also the lungs...

David Steensma: You can hear wheezes, if some airways are narrowed. [SFX] If the little air sacs, the alveoli, have fluid in them, you can hear them actually crackle as they open. [SFX] It sounds just like somebody's stepping on one of those bubble wraps. [SFX]

Fran: Doctors can also listen to blood vessels…

David Steensma: If somebody's had a stroke, you can listen and maybe you hear whistling [SFX] That suggests turbulent blood flow in those arteries, and that suggests the patient may have a narrowing. They may have an atherosclerotic plaque there.

Fran: And then there's the abdominal region.

David Steensma: 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. [SFX]

David Steensma: 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?" [sfx]

David Steensma: Sometimes that noise is so loud that we can hear it outside. [SFX: stomach rumbling] Our stomach's "rumbling" as we say, a phenomenon called “borborygmi,” which is a technical name for “rumbling stomach.”

Fran: So the next time your stomach’s rumbling, you can casually tell people, "Pardon my borborygmi."

[music out]

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

[music in]

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

Fran: That’s Dr. Daniel Weiss, a cardiac expert.

Daniel Weiss: One of them is passive capture of the sounds. Listen to the heartbeats. [rapid sfx] Have the patient take a breath in and out... [sfx] Listen to the abdomen by putting the stethoscope on the stomach… [sfx]

Fran: But that's not always enough. The sounds can be confusing.

Daniel Weiss: 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 soundalikes, but in fact stem from different physiologic conditions.

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

Daniel Weiss: Take a deep breath and hold it, [SFX] 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.

[music transition]

Fran: 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.

Fran: 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 patient's health.

That’s coming up, after the break.

[music out]

MIDROLL

[music in]

Fran: 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.

[music out]

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

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

[stethoscope heartbeat sound in]

David Steensma: When I was in my late thirties, I lost part of my hearing in my left ear. [left channel becomes muffled & quiet]

David Steensma: And, when my old medical school stethoscope finally wore out after some years, I got an amplified one. [turns on, heartbeat sounds now crisp and clear] And I couldn't believe how much of a world that it opened up again for me. [heartbeat sounds out]

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

[music in]

Daniel Weiss: 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.

Fran: Compare that to an imaging system, like an X-Ray or an MRI. [SFX: X-Ray or MRI]

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

Fran: And most importantly, sonic tools are really precise.

Daniel Weiss: 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.

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

Daniel Weiss: 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. [SFX - ascending tone] That's where babies cry and people talk. [SFX - baby crying + person talking]

Daniel Weiss: However, our worst hearing is at the extremes, at the close to 20 Hertz, which is the lowest we can hear… [sfx - tone down to 20 Hz] and close to 20,000 Hertz, which is the highest. [sfx - tone up to 20,000 Hz]

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

Daniel Weiss: Many, many of the interesting sounds are 400 Hertz or less, [sfx: 400 Hz going down] 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.

Daniel Weiss: And we believe that there's information buried in the higher frequencies as well, in the higher harmonics. [designed heartbeat shifting up high] And if you're not capturing that with a stethoscope, you're never gonna be able to see the patterns.

[music out]

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

Daniel Weiss: 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. [carotid artery - traditional stethoscope]

Daniel Weiss: 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. [carotid bruit - specialized stethoscope]

[The Cabinetmaker - Rose Ornamental [Blue Dot]]

Fran: By improving the quality of the sound that's captured, doctors can learn new things about how the body functions. Take swallowing for example. [sfx: swallow] We typically swallow hundreds of times each day without even thinking about it. But there's a lot more going on than we realize.

Daniel Weiss: When we swallow, there's an enormously complex sequence of events, physiologically, that occur. Your trachea…

Fran: Also known as your windpipe...

Daniel Weiss: …And your food tract, your esophagus, share a common beginning, right? The top part of your throat. And then they split.

Daniel Weiss: So how does the body know to let air go down into the lungs [sfx: inhalation] and food into the stomach [sfx: swallow] and not the other way around? So the way that 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.

Daniel Weiss: 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.

[music out]

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

Daniel Weiss: 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 [SFX - Swallow - Normal Stethoscope] because they didn't have the proper equipment or processing to be able to hear anything.

Daniel Weiss: 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.

Fran: To compare, here's a swallow heard through a normal stethoscope. [SFX - Swallow - Normal Stethoscope]

Fran: And here's the swallow recorded using a specialized, high tech stethoscope. See if you can pick out the five different stages.

[SFX - Swallow - Bongiovi Stethoscope]

Fran: Here it is even slower.

[SFX - Swallow - Bongiovi Stethoscope slowed down]

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

Daniel Weiss: 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. [SFX - EU Click]

Fran: Go ahead and try this yourself. The tough part is ignoring the sound coming from your throat, and only focusing on that click in your ear.

[beat]

[music in]

Fran: 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.

[clip: Living in Oblivion]

Daniel Weiss: 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.

Daniel Weiss: So we started listening to those click sounds. And our ENT said, “Wait a minute! We notice that the sound quality changes when there are different kinds of disorders in the ear.”

Daniel Weiss: And so we developed a special ear microphone to listen for the clicks. Forget the swallow, now we're just listening to the clicks.

Fran: This microphone basically looks like an earbud. Here’s that ear click, recorded using this new tool. [SFX - EU Click] And again. [SFX - EU Click]

Fran: 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.

Daniel Weiss: 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.

[music out]

Fran: These days, some stethoscopes go even further.

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

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

Daniel Weiss: For example, one of the companies has an AI that's FDA approved for pediatric murmurs. The accuracy of the AI was 94%, and the expert pediatric cardiologists is about 88% or 89%.

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

[music in]

Fran: 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.

Daniel Weiss: 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.” [SFX - Star Trek tricorder]

Daniel Weiss: They don't necessarily want that. They don't want to just put some data in, get spit out an answer, and "Now you’ve gotta go with it." They want to understand, “What is that system doing? How is it making that decision?” And it has to make sense to them.

[music out]

Daniel Weiss: So the first thing we realized is that we want to be able to always present the sound to the physician, both unprocessed… [mitral regurgitation unprocessed] and then with processing… [mitral regurgitation processed] to help them hear the difference.

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

[music in]

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

David Steensma: 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.

David Steensma: It felt like you were connected with these ancient physicians like Laennec, like Auenbrugger, 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.

Daniel Weiss: 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.

Daniel Weiss: 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.

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

David Steensma: 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.

David Steensma: 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, um, "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... [clarinet comes up] And which one is the oboe…” [oboe comes up]

David Steensma: 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 happened.

David Steensma: So not all sound-driven diagnosis is through an instrument. Sometimes it's just using the… the instruments that are on the side of our heads.

[music up, then under]

Twenty Thousand Hertz is produced out of the Sound Design Studios of Defacto Sound. Hear more at Defacto Sound dot com.

Fran: This episode was written and produced by Fran Board.

Other Voices: and Andrew Anderson. It was story edited by Casey Emmerling. It was sound designed and mixed by Jesus Arteaga and Joel Boyter.

Thanks to our guests, Dr. David Steensma and Dr. Daniel Weiss. And thanks to Joseph Butera from Bongiovi 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.

[music out]