Not uniquely human

Transcript

I’m a cardiologist. I do cardiac ultrasound. And I want to show you one of the tools of my trade.

This is my probe. It’s got a flexible tube down here, but on the tip it’s got a crystal, and this crystal is a camera. But I like to think of it as a kind of third eye because it lets me see deep into my patients’ hearts.

Let me tell you about the procedure that I do. I give my patients some medicine and make them sleepy. Some of my patients I put to sleep altogether. I then take the probe and I place it in the back of my patient’s mouth. Then I slide it down their esophagus, and when it’s in exactly the right spot, I turn around and I look at my monitor and this is what I see.

A beating heart. Two pumping ventricles below, the left atrium, the right atrium, the valves. This is a beautiful heart. If I showed this echo to 100 cardiologists, they’d all agree this is a perfectly healthy human heart.

But they’d be wrong about one thing. This heart is healthy, but it isn’t human. In fact, this heart belongs to a chimpanzee.

Across the animal kingdom, not all hearts are as similar to ours as a chimpanzee heart. But despite differences — and there are differences — hearts are pretty much the same. They serve the same function. Let me show you what I mean.

This is a cardiac ultrasound of a tiger’s heart. This cardiac ultrasound belongs to a dog. This heart belongs to an animal called a tapir. This heart belongs to a mandrill, beautiful animal. This belongs, the heart belongs to a California condor. And this is the heart of a python.

Now, cardiologists don’t usually show pictures of animal hearts, but I was given a special opportunity several years ago. I became a cardiovascular consultant to the Los Angeles Zoo. I helped the zoo’s veterinarians rule out a torn aorta in a gorilla, exclude congestive heart failure, in a sea lion, assess a macaw for a heart murmur. In this picture, I’m listening to the heart of a lion who had undergone an operation to remove a significant amount of fluid from her pericardial sac, the sac in which the heart is contained.

Working with veterinarians changed how I practice human medicine. Opening up to the world of animal medicine was transformative for me. I learned, for example, that no disease is truly uniquely human, from breast cancer and leukemia to sexually transmitted diseases, obesity, obsessive compulsive disorder — animals and humans get the same problems.

Along with my writing partner, Kathryn Bowers, we’ve been exploring this overlap between health and disease in humans and animals. But this experience also put me in a position to solve a medical mystery that’s puzzled cardiologists for a very long time.

When you think about cardiology, you probably think drama. You think about open heart surgery and maybe CPR and chest-clutching heart attacks. And we do see those things, and we do do those things. But much more commonly, we see a problem. We see it pretty much every day. It isn’t typically life-threatening, although it can happen when people are very, very scared. Wonder if you can guess what it is?

It’s fainting, of course. And cardiologists know a lot about fainting. We know a lot about the mechanics of fainting. We know what happens when an inadequate amount of blood makes it to the brain. And that happens for a couple of reasons, but one of the reasons is that the heart beats too slowly.

But you might be surprised by what we don’t know: we don’t know why. And if you think about it, it doesn’t make a lot of sense from an evolutionary perspective that an animal, maybe a hunted animal, terrified, would slump to the feet of its predators. I mean, shouldn’t natural selection have taken out the fainters in favor of the fighters and the fleers?

Well, here’s where working with animals and listening to animal hearts put me in a unique position, because I learned from veterinarians that animals from canaries to alligators to lapdogs in the face of danger can radically slow their hearts and sometimes faint.

Now, some of you may be thinking, “Wait a minute, wait a minute. That doesn’t sound right. What about fight or flight?” And you’d be right. Most of the time, an animal in danger, terrified, his body is flooded with adrenaline and that causes his heart to race and his blood vessels to constrict, and it readies him to fight or run for his life. But some of the time, the same part of the nervous system that causes that fight or flight does the opposite. It causes the heart rate to plummet very, very low.

Now, if you’re still skeptical, I would submit to you that every single person who’s sitting here has experienced this. Think of the wave of nausea you had when you lost your passport in Beijing, or that “I think I’m going to vomit” feeling when you accidentally hit reply all on a personal and sensitive e-mail, or when you momentarily lost sight of your toddler in the supermarket.

Now, most of the time, if you did a pulse check, if you could quickly do a pulse check, you’d find that your heart rate was kind of slow at that moment, but it would rapidly accelerate, galloping into that fight-flight we’re more familiar with. But sometimes, sometimes that slow heart rate persists and get slower, and then the woozy feeling comes on and then we’re fainting.

And it’s that super slow, slowed heart rate that’s the key to understanding why we faint. Because it turns out that animals, from deer to rabbits to iguana to fish, they come equipped not with two survival modes, but with three.

It isn’t fight or flight. It is fight, flight, or faint.

But why? What is the survival benefit of that? Well, to help think about that question, I want to show you one of the other tools of my trade.

My ultrasound probe allows me to see into my patient’s heart, but my stethoscope lets me hear hearts. You probably can’t hear your own heartbeat right now, and you definitely can’t hear the heartbeat of the person sitting next to you. But beat after beat after beat, hearts make noises.

The “bump-ba-dum, bump-ba-dum, bump-ba-dum” that your doctor hears when he put his, puts a stethoscope on your chest, that’s the sound of your heart valves snapping shut. And that’s true if you’re a mammal, an amphibian, a reptile or a fish.

Meet Oscar. I should introduce him by his Latin name, Astronotus ocellatus. But he’s known as the Oscar fish. These are freshwater fish, they’re related to tilapia, and they’re playful and energetic little fish. In fact, enthusiasts call them the puppies of the aquarium.

When Oscar fish gets scared, they do something very interesting. They go from swimming playfully to boom, floating, seemingly lifeless. Their fins barely moving, their respiratory rate’s very slow.

And if, in that moment, I were to take an aquatic version of my stethoscope and place it on Oscar’s body, do you know what I’d hear? “Bump ba-dum. Bump ba-dum. Bump ba-dum.” A super-slowed heart rate with lengthy pauses in between beats.

To understand why that might be useful, consider that many underwater predators are equipped with heartbeat detectors. They’re called ampullary organs, and they track the electrical impulses that come from fishes’ hearts. So it makes sense that if a fish could silence that beacon, he could become acoustically invisible and maybe save himself from being someone’s dinner.

Those of you who’ve ever seen a submarine movie will be familiar with this concept. You know the captain of the hunted sub tells his crew to run silent? They turn off the motors and the engines and the radios and they wait?

So slowing down a heart rate may help survival by silencing hearts, but it also keeps animals still. When scientists played recordings of wolf howls, nearby baby deer by fawn in brush, their heart rates plummeted. And the same thing was true with alligators and woodchucks and cats and monkeys. And the effect is more dramatic in the juveniles than it is in the adults, which is interesting because fainting is more common in younger humans than it is in older people.

Well, does this happen in human beings as well? This is the kind of experiment we could never do. I mean, we would never intentionally terrify infants to see the effect on their heart rate. But an accident of geopolitical fate actually gave us some insight into this question.

In January of 1991, at the beginning of the first Gulf War, Scud missiles were fired into Israel. The citizens were alerted to the Scuds being fired by loud blaring sirens that were blasted from speakers outside and from radios and televisions inside.

On the evening of January the 18th, 1991, three women were in labor on the maternity ward of a Tel Aviv hospital. A Scud missile was fired and the sirens blared. And the nurses who were monitoring these women noticed something remarkable. The heart rates of all three babies plummeted from 130, 140 to 30 or 40 beats per minute.

These babies, although they hadn’t even left their mothers’ bodies, were equipped with the ancient protective stilling physiology shared with creatures across the animal kingdom: fight, flight, or faint.

Fainting halts the action. It diffuses conflict. It can enable escape. And embedded in ancients’ physiology could be a lesson for how we deal with the things that scare us the most in our lives. Because fighting or fleeing may work some of the time, but when you can’t run away and you can’t or you won’t fight, sometimes being still offers powerful form of protection.

The crystal at the tip of my probe let me see into my patient’s heart. But when the veterinarians at the Los Angeles Zoo opened the door and invited me into their world, it allowed me to see between hearts and across species. And this allowed me to solve a medical mystery.

Human beings are animals. And that means that all of us doctors, we’re all veterinarians. If human doctors could look beyond our single-species focus, we might be able to solve more medical mysteries: some like fainting, some life-threatening, some crucial to global health. And this would benefit not only humans, but all of the patients on the planet. Thank you. (applause)