Christian Eriksen's heart device, and air leaks on the ISS

0:01All engine running. Absolute genius. Get this. Welcome. Welcome. This is the show where we bring you science. What that essentially means is discovery is advances. Research. Technology. Unbelievable. Without further ado, this is the Naked Scientist. Hello, welcome to the Naked Scientist podcast, the show that brings you the biggest breakthroughs and talks to the major movers and shakers in the worlds of science, technology and medicine. With me, Chris Smith. And coming up this week, how an implantable defibrillator saved the life of Danish footballer Christian Eriksson. Russian cosmonauts fix an air leak aboard the International Space Station.

0:38What did that involve? And the dinner dilemma of Richard Feynman and his friend resolved by a maths equation.

0:52The 2026 FIFA World Cup is getting underway in Mexico, Canada and the US. And for many, it's a religion. Indeed, the revered Liverpool manager Bill Shankly famously said, some people believe football is a matter of life and death. I'm very disappointed in that attitude. I can assure you it is much, much more important than that. Denmark's talisman, Christian Eriksson, would no doubt disagree with Shankly. In the course of his glittering career, he's collapsed on the pitch twice now. Eriksson's heart reportedly stopped for five minutes in a European Championship match between Denmark and Finland back in 2021.

1:32Thankfully, he was resuscitated and then had an implantable cardioverter defibrillator fitted to keep tabs on his heart and to step in to restart it should anything go awry again. well that did happen just recently during a friendly the other day against ukraine when another collapse saw the device restart his heart and he was thankfully able to walk off the pitch shortly afterwards now all this got me wondering what these amazing life-saving devices look like and how they actually work so i asked my colleague stephen pettit who's a consultant cardiologist at the royal papworth hospital to pop by with one for me to look at so this is an implantable cardioverter defibrillator or ICD as we call it and this is a device that we use in patients who are at risk of life-threatening arrhythmias, heart rhythm disturbances, to automatically detect and treat those.

2:27It is palm-sized so it's pretty small. Yeah an ICD will fit in the palm of your hand. The sizes of these devices have come down over the years when they were first developed 30 or 40 years ago, they were actually the size of a house brick and were implanted in the abdomen because that was the only place there was enough space for them. But as you say now, they fit in the palm of your hand and they're implanted in a manner almost identical to a pacemaker. Where does it go? So the device sits just above the left chest wall underneath the collarbone, around about a centimetre below the skin. It is attached to an electrode, essentially like a floppy piece of spaghetti and we feed that electrode through the venous system into the heart and within the heart it sits watching the heart rhythm.

3:16Which bit of the heart is it in then? All defibrillators that are put in through the venous system have an electrode in the right ventricle. Some of those defibrillators have leads within other places of the heart to help them sense and detect different types of heart rhythm disturbance or to help with them pacing the heart. And the lead, is that listening to the heart, but also the way it can talk back to the heart? The leads do two things. They sense and they pace. And it's looking at electrical signals within the heart. And then at any stage, if it sees a troublesome electrical signal, it can respond to that either by pacing or in the context of a life-threatening rhythm disturbance by charging and delivering an electric shock.

4:01When you say pacing, is that it sending impulses down the connection then which the heart picks up and responds to? Correct. Defibrillators and pacemakers, the vast majority of them work on a demand principle where if the heart has its own electrical activity it will just sit back and watch. But if there is a gap it will fill that gap in. It will deliver an electrical impulse to the heart and stimulate a heartbeat. How does it know when the rhythm's wrong then? That's where defibrillators get very clever. So we program them to recognize very, very fast heart rhythms as abnormal. So if you and I were to go for a bike ride or a run, we could probably get our heart rate up to 170 or 180, maybe even 190 beats a minute.

4:45But we would not get it up to 260, 270 beats a minute. Those that are just too fast to be a normal heart rhythm. And it's those rhythms that they treat with electric shocks. why would someone get a heart rhythm like that that's a very very good question and one that fundamentally we don't know the answer to people with uh certain types of heart condition are vulnerable to heart rhythm disturbances probably the most common risk factor for these sorts of heart rhythm disturbance is a person who's had a heart attack and myocardial infarction in the past but there are lots of other forms of heart muscle disease you know inherited forms of heart muscle disease that can lead people to be vulnerable to heart rhythm disturbances.

5:26But why that heart rhythm disturbance happens on a particular minute of a particular hour of a particular day, we have no idea. And that's really why defibrillators exist. I mean, if we knew that someone was going to have a heart rhythm disturbance next week, well, we'd bring them into hospital before it happened so that we could treat them immediately. But we don't. The risk is there all the time as people go about their normal lives. And so that's why defibrillators are implanted to provide that constant backup. Is it anything to do with extreme exercise? Because this does seem to happen to a number of footballers.

5:57And is it anything to do with the fact they're putting huge demands on their body? Or is it just that they are the most monitored athletes in the world? So when it happens to them, we notice? I think probably the latter. If a footballer has a cardiac arrest on a football pitch, then that's news all around the world. But if a gentleman has a cardiac arrest on the high street whilst he's doing his shopping then that tends not to make the you know the news at 10. If you look at reports from the London Marathon every year there will be you know some poor runner develops problems and ends up needing to be resuscitated.

6:34Now when this device detects a dodgy rhythm and resets the heart rhythm by delivering a shock is that effectively doing then what you see in in all the movies when people put an external defibrillator they put the pads and the paddle's on the chest and the person jumps off the bed. Is it effectively doing that but from the inside? Yes, it's exactly what it's doing. So it's delivering a high voltage shock, but because the electrical impulse is being delivered right inside the heart, the energy levels that are required are less than with external defibrillation where the electrical current has to pass through all of the chest wall to get to where it's needed.

7:15How does that work then? Why would giving the heart an electric shock stop that rhythm? Again, a very, very good question. I tend to think of this a little bit like fire breaks in a forest. When you have a heart rhythm disturbance like ventricular tachycardia or ventricular fibrillation, you've got very chaotic electrical activity within the heart and the normal heartbeat doesn't get a look in. The aim of defibrillation is really to reset electrical activity in every single bit of the heart, and there will be then a pause, and then the normal heartbeat has an opportunity to come back. The device you've got in your hand doesn't have any wires that would come out through the body, so has it got its own power source?

8:01It's completely self-contained? Yeah, absolutely. So there is a battery within the defibrillator, and the average life expectancy of one of these devices is probably somewhere between six and eight years and essentially it's got almost like a fuel gauge in a car we see when it's getting down towards you know towards empty and then when the red light comes on patients are invited back into hospital to have their to have their battery changed how much does it cost this device in the palm of my hand costs in the region of 10 to 15 000 pounds so they are they are not cheap but they are very very effective ways of reducing the risk of sudden death for for those of us who are vulnerable to sudden death by virtue of having a serious heart condition and the reassurance of knowing you're in good hands though priceless thanks very much to steven pettit at the royal papworth hospital birds use a variety of strategies to navigate now they have excellent vision so that usually takes precedence, but when visual cues are not available, such as during overcast, nocturnal or in unfamiliar surroundings, they can instead rely on the Earth's magnetic field using some kind of inbuilt compass.

9:13But we don't know how they do it. Now though, intriguingly, researchers in Germany have identified that a type of big iron-containing white blood cell called a superparamagnetic macrophage, which is found in the liver, seems to hold the key. They found that if they deplete this population of macrophages, pigeons lose their ability to sense the Earth's magnetic field. Christian Kurtz is at the University of Bonn and Martin Vikelsky is at the Max Planck Institute of Animal Behaviour. Well, we know that animals can follow a magnetic direction. But how they do that, for example, songbirds that migrate from Europe into Africa every year in the billions, how they do that, we didn't really know.

9:58How do we know it's magnetic, Martin? Well, at night, in complete darkness, or when the sun is not out, when it's completely occulted, then they have to use a direction sense because they follow a line for hundreds of kilometres. And we also manipulated that sense before, so we know they have a magnetic direction sense. So if you put birds in an artificially influenced magnetic field, they'll go the wrong way? Yes, you can do that, exactly. So in this present study, what were you going after to try to work out what might be the origin of this magnetic sensitivity, Martin? Well, it was a total chance event.

10:37We were not searching for something. We were just getting together. And then Christian said, hey, I have these cells in the body that are magnetic. And I said, well, that's really crazy. Shouldn't we join up and, you know, look at how that may affect magnetic sensing in animals? And that's how it came about. And then, you know, we went on this voyage together and everything was falling into place. It was crazy. It's a crazy idea. And then it seemed to really be true. Magnetic cells, Christian. I'm intrigued. So were we. I mean, we kind of stumbled over them during a technical study, and we published them more than 10 years ago just to make people aware that they exist and that people have to be aware of them if they perform experiments that they don't draw misconclusions.

11:25So when Martin and I, by chance, met on a meeting, he was mentioning that nobody has found cells that can respond to magnetic signals in the body. and I told them, well, we just stumbled over them and then we had this eureka moment. Let's go after them and test whether they play a role in animal migration. What are the cells and how do you know they're magnetically sensitive? These cells are immune cells. They are called macrophages. Macrophages exist in all tissues of our body. They are like the vacuum cleaners. They remove debris or material that should not be there to avoid inflammation. and these particular macrophages occur only in the spleen of mammals or in the liver of birds and one of their jobs is to degrade old red blood cells.

12:15You know, red blood cells supply the body with oxygen and the molecule that does that is called hemoglobin and hemoglobin contains iron. And so when you degrade these hemoglobin-containing cells, The macrophages make little storage compartments where the iron is put. And at some point, it gets released to the bone marrow to make new red blood cells. But before this happens, the macrophages, they have little iron magnets within them. And with them, they can respond to external magnetic fields. How do you know that they respond? What actually happens if you magnetize the cell? What does it do? That's really exciting because regularly, you know, these birds, like homing pigeons, they can be trained to fly in a certain direction, let's say east.

13:01But when you have complete cloudy days, like no sun coming through, really, really low clouds, they still find their way home. And that's when they use the magnetic direction sense. But Christian had this idea, well, we can knock out these macrophages, these cells that have the iron inside, the sort of the little magnets inside. So we did that. And when we released the same pigeons without these macrophages, without these cells, then they were completely lost. As if you are in the woods and, you know, you have no compass and you want to get out and you are getting lost. You still try to wander out, but you go in all kinds of directions.

13:39That's what we found. And that is super exciting because it did show that these cells, these iron containing cells are responsible for the magnetic direction finding. Christian where did you knock them out from do they migrate from the spleen or the liver and go to other tissues such as the brain where they could pass signals or respond and pass signals into the nervous system or is this originating from the liver and the spleen well as far as we can say they are residential they stay in the organ where they perform their job they don't go to the brain at least we haven't found it we have checked most tissues of the pigeons and we found them only in the liver so they seem to be residential so martin how do you think this is working then because i mean there are nerves that run through the liver and the spleen are they talking to the nervous system or is there some other mechanism by which something in the liver and the spleen which are two abdominal organs can affect behavior that's i think the super exciting part we have our cell biologist clivia clivia lisowski who actually investigated that primarily And she showed that these cells sit next to the vagus nerve endings.

14:48So there's the nerve in the liver, and that doesn't go directly into your conscious brain, but it goes via your backbone into the brain. So it's sort of this gut feeling that when a bird moves through a magnetic field, through an external magnetic field, the Earth magnetic field, then we think these iron particles in the cells are sort of bumping against the cell walls and make a signal there. And then the cells pinch the nerve. And that's how the information goes then into the brain via the backbone. So this is super exciting. So we think that, you know, from the outside, external information is entering these cells in the body and they transmit it unconsciously to your brain.

15:37So that's, we think, really a confirmation of gut feeling. Both metaphorically and physically. Can you actually see the cells doing this or can you measure anything, Christian, in the cells that shows you they are responding in this way and that they are passing information to those vagus nerve endings? In principle, this is possible and we are planning to do that for the future studies. So how exactly the cell biological alterations resulting from sensing magnetic fields, how they translate into nerve activation, this is a big question and that requires a dedicated study on its own. We use the term gut instinct much more cautiously in future.

16:15That's an amazing story though, isn't it? Christian Kurtz and Martin Vekelsky there, they just published those findings in the journal Science. The Naked Scientist podcast is produced in association with Spitfire, cost-effective voice, internet and IP engineering services for UK businesses. Find out how Spitfire can empower your company at spitfire.co.uk. Music in the programme is sponsored by Epidemic Sound, perfect music for audio and video productions. This is the Naked Scientist podcast with me, Chris Smith, and still to come, how maths can help us to resolve a dinner dilemma. But first, astronauts have now returned to the International Space Station after repair work was carried out on persistent leaks in the Russian part of the satellite.

17:04Five of the space station's crew members were ordered to shelter in SpaceX's shuttlecraft and to brace for potential evacuation. Meanwhile, the two Russian cosmonauts who remained on board attempted to plug the leaks. Rachel Ralph caught up with Richard Hollingham from the Space Boffins podcast to bring us up to speed. There was a lot of drama when suddenly we got this message from NASA saying they've evacuated five astronauts into the SpaceX capsule, sealed them in, and you had two Russian cosmonauts fixing this leak. So, you know, this sort of came out of nowhere, but actually it really didn't come out of nowhere because this particular module is called the PRK, which connects to the Zvezda service module on the International Space Station, has actually been leaking since 2019.

17:57So it was really unexpected that they suddenly decided to fix the leak now. And it looks like they've at least partially fixed the leak on the space station. They've used something, I love this, it's actually a patented sealant called Germitol 1, which is essentially some sort of sealant and cloth that they use to put over any potential holes in the spacecraft. At the moment, everything seems to be stable. So like you said, these air leaks started in 2019. So what's actually prompted this heightened concern and caused the evacuation of the astronauts? I don't think we're entirely clear other than the Russians decided to fix it now because the leaks don't seem to have been getting any worse, or at least as far as we know.

18:44But this is old, this spacecraft now. So this was designed in the 1980s. It was going to be the successor to Mir. It was built in the 1990s. It's been in space for almost 26 years. So it was launched in July 2000. And, you know, it's a really harsh environment there. There's all sorts of particles. They could also have been errors. It's being docked with constantly. This is a tunnel leading to a docking port. So it's under all sorts of strains. And I mean, the bottom line is it's getting old, it's getting worn. And how much longer it's going to last is the big question. I presume that this emergency evacuation kind of demonstrates how seriously the air leaks were taken.

19:31But what would have happened to the other two crew members who stayed on board to fix the leaks if they needed to be evacuated as well? It's important to understand that these are leaks, these are tiny leaks, it's a small amount of air leaking out. So it's not catastrophic. It's nothing like, you know, the film Gravity, where suddenly the spacecraft's bombarded by all sorts of stuff and there are holes everywhere. It's really nothing like this. So this was a contingency, and I think it shows the care and the attention that the space agencies put into the welfare of the crew. I mean, it was really an abundance of caution here.

20:05And if something had gone really badly wrong, well, everyone can get quickly to a spacecraft. And the point of putting the astronauts in the spacecraft was they could undock from the space station if there was a major problem and just get out of the way. Those two crew that were fixing the leak, yes, they were probably under more peril, not really, because, you know, it's unlikely that it would suddenly rupture. So they They were probably at risk the most. But if it had got worse, they could just get out, shut the door and get into their Soyuz capsule and get off the space station. So, you know, it's really an abundance of caution.

20:40I think it shows that astronaut welfare absolutely comes first here. So like you said, astronaut welfare does come first. And these astronauts live in a perilous environment. So why haven't the leaks been properly repaired before, I guess? They've been partially repaired, like you said, especially now, but why not fully? It is absolutely a perilous environment, 400 kilometres above the Earth, going at 27 ,000 kilometres an hour in the vacuum of space. And it's low Earth orbit, so there's lots of other debris sort of spinning around there. And it's an old space station. I mean, I wouldn't want to do it.

21:16The leaks themselves, we're probably going to see more. They're, you know, sort of hairline fractures. I think the bigger concern would be if a large piece of space debris hit the space station or one of these really started to rupture. I mean, they could seal this area off. Think about like a submarine where you have hatches between the various sections or ships as well have that. So, you know, they can seal off sections of the space station if there is a bit more of a problem. I think we are going to see more and more of these leaks over the next few years. At the moment, the plan is to take the space station out of orbit, well, you know, push it out of orbit in 2030, maybe 2032.

21:54But it's a question of kind of keeping it going in the next four or five years. So with the plans to decommission the ISS in 2030 or 2032, are there plans to potentially have a replacement space station at all? There is no space agency plan to have a replacement space station, but there are plenty of private companies. And that's kind of the point. So NASA, who is leading on all this, wants to sort of make way for small private operators of space stations. And there are several being built by several companies. Whether they'll all fly, it's unclear at the moment. But that is the plan. So we will see the end of the International Space Station.

22:35So this great international endeavour where you still got, you know, American astronauts working alongside Russians despite the war in Ukraine. And so that's going to be replaced where they think small private space stations, maybe more robotic craft, and then NASA is pushing forward and putting all its efforts into getting astronauts back on the moon. Richard Hollingham speaking to our own Rachel Ralph. Many years ago, the Nobel Prize winning theoretical physicist Richard Feynman went for dinner with his good friend Ralph Leighton. They dined at this restaurant many times before, and so Leighton wondered whether he should opt for his traditional favourite dish, or be bold and choose something new, given there was, of course, a chance that it might not be as good as the one he knew he liked.

23:22Now, this is a classic maths conundrum, which is known as an optimal stopping problem. We run into them all the time. But it prompted Feynman to scribble down a mathematical solution there and then at the dinner table. Luckily, Leighton kept the handwritten notes, but he struggled in the aftermath to make sense of Feynman's cursive writing. Now, though, 50 years on, a team of researchers have found a copy of those scribbled workings, and they've decoded Feynman's extremely elegant solution to the dinner problem. Richard Webber is an emeritus professor of maths and also a fellow of Queen's College at the University of Cambridge, and has literally written the book on these very problems.

24:01So he's the perfect person to take us through it. It's a story of 50 years old. Sometime in the 1970s, Richard Feynman was sitting at lunch at a Thai restaurant in Gunderdale, California, with his friend Ralph Leighton, and they were trying to decide what to have for lunch. And Leighton was wondering whether he should have his favorite dish, which was ginger chicken, or whether he should try something new in the hope of finding a dish that was even better than ginger chicken. Finally, he immediately saw this as a mathematics problem. He began writing down on a napkin what he thought the solution would be.

24:33The solution he came up with was a very beautiful one. He said that what you want to do, you want to try and maximize your total satisfaction. And so at each day, you should look at the number of days left that you might be going to this restaurant. You compute a threshold. The threshold has an interesting square root form. It's the square root of the days left divided by the square root of the days left plus one. And this is a threshold which, when the number of days left is huge, is close to one. But when the number of days left has reduced to just one day, then the threshold is equal to a half.

25:06And so the idea is that at the very beginning, when there are many days left, the threshold is high. A meal has to be extremely good if you're going to want to stick with that one. But as the number of days left gets closer to zero, then the threshold drops. And a restaurant that's only medium good might be the one that you now want to stick with. And why is this now a consideration? Why are people talking about this now? Well, apparently people have sort of known that Feynman considered some restaurant problem for a long time. but they hadn't really been able to track it down. But recently, three researchers, an international team, found this napkin on which Feynman had scribbled and were able to study it, piece together the problem that Feynman had been thinking about, re-solve it, and then go on to see what do real humans do when faced with the same problem.

25:57Because this is actually a kind of broad form of problem, isn't it? They call it the optimal stopping problem because we encounter this in everyday life all the time. how long should I go prowling around the car park looking for the perfect parking place how many people should I date before I decide to marry one of them for example that life is full of these sorts of things exactly those are two very good examples the secretary problem I'm going to interview people for a job and as I see each person I have to decide do I want to hire this person or not and if I send them away perhaps they're never going to come back that problem has a beautiful answer.

26:31It says that what you should really do is you should interview about 37 % of all the people. And don't choose any of those, but then choose the best one you see thereafter who's better than all those you've seen previously. Now, Feynman's problem is an easier problem because you can always go back to an earlier choice, and that made the problem a little bit easier. The researchers who wrote the recent paper were not pure mathematicians. They were what are called computational cognitive scientists, and they wanted to use Feynman's sort of little napkin restaurant problem as a baseline to answer a deeper problem about how do real human brains handle economic trade-offs.

27:08And so they recruited a panel of, I think, 2 ,520 people. They looked at people going on holiday, and they said your holiday is either going to be seven days, 14 days, or 28 days, and you're going to go to one of four possible cities where the distribution of restaurants are different. And they just look to see what would people do when trying to solve a problem of focusing on homing in on the best restaurant and maximizing their enjoyment over the length of holiday. Now, of course, human brains aren't equipped to compute that square root formula that I mentioned a moment ago. What they found is that humans instead used a linear function where the threshold, instead of dropping like a sort of square root formula, instead drops linearly.

27:52So perhaps when you begin your 14-day holiday, the threshold that a restaurant has to meet in order to be the one you commit to is maybe 90%. But then as you go down to only two days left on the holiday, then a restaurant that's as good as 60 % is one that you would want to use for the last two days. So a linearly declining threshold. Now, the amazing thing is that using a linearly declining threshold is not optimal, but it gets to within 99 % of the optimum. what's amazing is that we do this at all so why do we have or why have we evolved to be so adept at these sorts of things humans face stopping problems all the time now primitive man wasn't going to tie restaurants and choosing ginger chicken but primitive man certainly had to meet deadlines of the sun going down winter coming and so all the time faced with these sort of stopping problems.