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The heart is so biologically central to our bodies, and so superficially simple—just a blood pump!—that you might be forgiven for thinking that surely scientists have already unlocked all of its mysteries. But there’s still much to learn about our hearts, as author Rob Dunn learned in the course of writing his new book, The Man Who Touched His Own Heart. We got to chat with Dunn recently about chimp hearts, the ancient Roman doctor Galen, and much more:
(Note: This interview has been lightly edited for length and clarity.)
World Science Festival: What made you want to write a whole book about the heart?
Robert Dunn: I’ve written a fair amount about how little we know about some of the unusual bits and pieces of the human body—the extent to which we’ve only just recently figured out what the appendix does, or what the axillary organs in the armpits do. But the more I worked on and wrote about humans, the more clear it became that some of our central organs are still pretty stinkin’ mysterious. And humans have been thinking about the heart forever, but it’s had a really herky-jerky history in terms of when major discoveries have occurred. So I drifted toward it because it became so central and so unknown, and it was hard to look away from all that.
WSF: Do we know anything about how much our hearts have changed from our primate ancestors?
Dunn: If you had asked that question in 2010, people would have answered that the hearts of other primates are pretty similar. If you look at them they look similar; there were even attempts in the 1960s to do a heart transplant from a baboon into a human. That was thought to have failed, not because of some fundamental problem with the transplant, but because the recipient was just in too bad a shape.
Then starting around 2005, Ajit Varki at the University of California, San Diego started to make inroads in comparing chimpanzees to humans and started to see a bunch of ways in which chimps were actually pretty different from us, in terms of how they got sick. It wasn’t until mid-2011 that the first paper came out actually comparing the illnesses of the hearts of chimps and humans. The shock of that paper is that while chimps and humans both get heart attacks, and they seem pretty similar, superficially, the heart attacks chimps were having were totally different. Instead of having clogged arteries, which is what happens to us, what the chimps were getting was a kind of fibrosis—imagine that you’ve woven the strings of the heart muscles so they crisscrossed in the wrong direction, and those crisscrosses prevent the heart from contracting normally. We don’t get that.
WSF:This is just speculating, but I wonder how much that difference is related to bipedalism and needing to pump blood in a standing-up position?
Dunn: That’s a fascinating question! It is possible—bipedalism imposes different consequences on how blood has to be pumped. You can imagine it leads to differences in blood pressure. For example, we know that giraffes have to have very hard arteries to get the blood all the way up to their head. So you might predict that there’s a little more brittleness in our arteries.
Most people talk about how the difference stems from probably the fact that chimps don’t eat bad food like us, but chimps in zoos eat this Purina monkey chow. If you look at their cholesterol levels, they’re like a meat-eating Jersey guy. So it’s not that.
What has been thought of is that part of the problem is the difference in inflammatory responses. We do know that of the small percentage of genes that are different between chimps and humans, many are immune genes.
WSF: Most people probably think the heart is just some simple pump, so it’s startling to think about how much we don’t know about it.
Dunn: I couldn’t agree more. It’s still very much true that if you could get a heart transplant as opposed to an artificial heart, you’re better off. More recent versions of artificial hearts have been attempts to model the heart with computers; those efforts take enormous supercomputers that take up many rooms, even those efforts can’t reproduce the dynamics of the heart, all they can get is a simple beat. That’s pretty amazing.
WSF: From all your conversations with scientists, where do you think the hottest areas of heart research are?
Dunn: One of the places I see people making some interesting advances is in comparative studies of the heart—trying to see how we compare to birds, other mammals, reptiles, et cetera. Recently there was a big breakthrough in congenital heart deformations that mostly came from understanding the history of when the different divisions in the heart chambers evolved, and which genes were associated with that evolution. That’s the kind of discovery where there’s a lot of opportunity for big advances.
And if you look at the number of heartbeats mammals get in their lifetimes, it tends to be pretty consistent: about a billion. There are some animals that get more than a billion, though—what allows them to get more out of their bodies? There are big, practical insights from those sorts of comparisons.
WSF: Do you think that Galen or other ancient Roman physicians would be surprised that we use the heart as a metaphor for love?
Dunn: I don’t think so. Galen did do some studies on how heart rate changed in response to lust and love. It’s not totally clear what those experiments were, but he was clear there was this link between the heart and our emotional responses. He wasn’t thinking of the heart as a symbol of love, but he was thinking about how his pulse would quicken at certain moments in his life. Galen was this absolutely fascinating dude, and a huge proportion of modern medicine is based on his insights. We tend to think of him as being dopey and getting stuff wrong, while forgetting that he was doing his thing 3,000 years ago.
WSF: So, did you think Galen was a dope before you started writing the book?
Dunn: It’s easy to think of all our scientific forebears as dopes! Like, you look back and think, how could they think there was air in the arteries? But every generation thinks the ones before them were dopey. So it’s clear the next generation will think we’re dopes.
WSF: It’s just a question of what we’ll be wrong about.
Dunn: Yep, it’s always hard to imagine how ignorant we are.
Except from The Man Who Touched His Own Heart
In this passage, Dunn examines one of the great explorers of the heart, Leonardo da Vinci, who not only enlarged our understanding of heart valves, but of blood flow as well:
“Once da Vinci had characterized the physical attributes of the heart’s valves, he sought to understand how they worked. He couldn’t see the valves functioning in living animals, so instead, he returned to a physical system, the river, to understand a biophysical system, that of vessels, blood, and valves, and to make predictions about its function. This approach of using one system to model another is among the most common modern practices in science, but that was not the case in the time of da Vinci. Based on his river studies, da Vinci predicted, correctly, that blood would move more rapidly through narrower blood vessels. On average, it does. He also predicted that when the big left ventricle in the heart contracted, it would be difficult to keep blood from flowing back through the aortic valve into that ventricle before the valve shut. This valve opens and shuts about once a second. As a consequence, it must seal both tightly and rapidly. Da Vinci thought the answer to how this occurred was in vortices, little eddies of blood that formed in part because of bulges in the aorta just above each valve (later to be called the sinus of Valsalva, for the Italian anatomist). Da Vinci tested his prediction by blowing a glass version of an artery in which he could watch the movement of grass seeds in liquid; it was, in essence, an artificial aorta. In watching the seeds, he saw his ideas confirmed, at least to his own satisfaction. He imagined that as blood flowed through the valve at the exit of the left ventricle, eddies of blood would form to help to close the valve. He was right, though no one would realize it until 1968, when two engineers, Brian and Francis Bellhouse, confirmed da Vinci’s prediction using a method essentially identical to the one he had used: they built an artificial aorta and watched the movement of artificial blood. When they published their article, the Bellhouses assumed they were the first to notice these vortices. It was only a year later that they discovered that da Vinci had beat them to the punch by four hundred years.”
Excerpt from The Man Who Touched His Own Heart by Rob Dunn. Published by Little, Brown and Company. Reprinted with permission.
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