Extreme Physiology: Everest to Ocean Floor

Extreme Physiology: Everest to the Ocean Floor
13 June 2013
Presented by Chris Smith, Kate Lamble


How can an ascent to the top of Everest help to save lives in intensive care? This week we're exploring physiology at the extremes: altitude, depth and cold. How does the human body adapt and cope under these conditions? Also, news of improved gene therapy techniques for sight-loss disorders, when do babies become sympathetic, how to cloak your cat (or goldfish), and have scientists discovered the remains of the Tunguska meteorite that smashed into Siberia in 1908?

In this episode

00:54 - Gene therapy focused on eyes

Scientists in America have developed a new virus that can deliver therapeutic genes to treat retinal diseases...

Gene therapy focused on eyes

Scientists in America have developed a new virus that can deliver therapeutic genes to treat retinal A womandiseases.

A number of sight-loss conditions are known, including some that are genetic and which, if treated early, are potentially preventable. The stumbling block, though, is a lack of suitable "vectors" capable of carrying protective or therapetics genes to vulnerable retinal cells.

Scientists have had some success with modified viruses, but the current generation of these agents can only reach a limited number of retinal cells and administering them also tends to cause inflammation and tissue damage.

Now UC Berkeley researcher David Schaffer and his colleagues have developed a strategy to produce a generation of superior gene therapy vectors, which appear to be at least 5-fold more effective than their forbears.

The Berkeley team's approach was to take an adeno-associated virus, which has a strong track-record as a gene therapy vector, and add a short sequence of 7 genetic letters - in random locations - within the gene coding for the viral coat.

This has the effect of changing the structure of the viral surface, altering how well it can stick to certain cell types. The team injected mixtures of these viruses into the eyes of experimental animals and then, a short while later, removed the rod cells from the eyes and used DNA-copying techniques to extract the genetic sequences for any viruses they contained.

These sequences were used to produce more of the same viruses, and further rounds of selection were then performed by repeating the process a further two times. The result was a virus dubbed 7m8, which showed a strong preference for retinal rods, cones and other nerve cells.

In tests, the new vector was capable of reaching and delivering a marker gene to 5 times as many cells as other equivalent vectors.

Sight-injurious injections beneath the retina were also not required as the virus was able to make its way to the target rod cells without being mopped up by the other tissues inside the eye.

Administered to mice with a genetic sight-loss condition called retinoschisis, which is caused by a defect in the retinoschisin gene, a 7m8 virus endowed with a healthy copy of retinoschisin prevented the breakdown of the retina normally seen with this disease and normal retinal electrical activity was preserved over a 4 month study period.

Tests on monkeys also led to successful targeting of the virus to the light-sensitive cells of the fovea, the part of the retina responsible for precision vision.

In their paper, in Science Translational Medicine, the researchers speculate that the superior results might be because the alterations to the coat of the modified virus make it less likely to stick to the "wrong" cells or other structures, which "enables enhanced penetration through retinal layers."

A brutal square attacking a circle

04:33 - At what age do we learn sympathy?

Babies display signs of sympathy from ten months old ...

At what age do we learn sympathy?

A brutal square attacking a circleSympathy is crucial for human co-existence. It's one of the factors why society is able to function, but we've never fully understood how it develops. 

Newborns respond to others in distress through emotional contagion, which means that if they see someone smiling, they smile too and if they see someone crying, they start crying. Then around about 2 years old, toddlers start to comfort their friends if they see that something bad has happened to them. But we haven't really understood what happens between these milestones. 

That question is what Yasuhiro Kanakogi and his team from Kyoto University in Japan have been working on and they published their work in PLoS ONE this week. The researchers made some animations of a blue ball and a yellow cube. During the animations one of the shapes was 'bad' and one of them was 'good'. The bad shape chased the other one around, hitting it and eventually, squashing it. They showed these clips to 40 children 10 month old children and then tested their reactions to the shapes afterwardsto see if they preferred the agresssor or the victim.

The researchers watched the subjects eye movement, but they didn't preferentially look at one shape over the other. However when offered a choice of the shapes after the video a significant majority preferentially chose the victim. To ensure that the children were not just scared of the agressive shape, the team then introduced a neutral shape (a red cylinder). Again, although there was no evidence of preferential looking, when offered a choice between the victim shape and the neutral shape, they chose the victim. And when asked to choose between the neutral shape and the aggressive shape, they chose the neutral shape.

Although more research will need to be done to examine how this effect fits into the long term development of sympathy, the task showed that from 10 months old, children understand the causality of an agressive event and without reacting to an emotional response (the shapes didn't appear upset, ruling out emotional contaigon) preferentially chose the victim, suggesting a rudimentary sympathy for others.

The One Ring... Frodo's secret means of gaining invisibility

07:17 - Cloaking device developed, for fish

A team in Singapore have developed an invisibility cloak that can hide goldfish and cats...

Cloaking device developed, for fish

The dream of invisibility goes back to at least the Greeks whose god of the underworld, Hades is supposed to have had a helmet of invisibility.

But this week scientists at the Nanyan Technological University in Singapore, unveiled a video of a goldfish and cat disappearing and reappearing behind a new 'invisibility cloak' they'd developed. If you haven't seen it yet you can find a link to the video below but in the meantime here's the Quickfire Science...

At the moment objects like tanks can only be disguised, using cameras to project the view behind the tank onto screens covering the other side. This was seen on a car in the James Bond movie, Die Another Day.

However this technology only works from one perspective - the angle the camera is facing - so if you spotted the tank from a different angle, it would distort the illusion.

But in 2006, British Researcher Sir John Pendry came up with a way of bending light around an object to create a 'cloak', which would make it invisible to the naked eye.

However when light waves are bent around an object they have to travel further than the light unaffected by the cloak. This means the bent light arrives slightly later than it should so the image isn't perfect.

To correct this, the bent light waves have to appear to move faster than the unaffected light travelling in air, which is impossible with natural materials.

Cloaks like this have been built successfully with artificial 'metamaterials', made with carefully designed structures smaller than the wavelength of light. But they've only been able to hide objects from view in microwaves rather than visible light.

To disguise large objects in visible light, the team in Singapore decided to see how well they could manage with conventional materials, not worrying about whether the light was delayed.

They used prisms of glass in a hexagon or square which refract the light through one another around the object - so even if your pet moves inside the prisms it looks like it has disappeared!

This can still only be seen from a maximum of six angles but the hope is that they will be able to increase this by changing the layout of the prisms.

They have managed to hide goldfish and even a cat in a real life environment and hope it could be used for both surveillance and entertainment.

09:49 - Tuguska Fireball meteor fragments found

Scientists have recovered material from a gigatic explosion in 1908 which destroyed thousands of square kilometres of Siberian forest...

Tuguska Fireball meteor fragments found

The aftermath of the tunguska meteoriteMark - More than 100 years ago, back in 1908, a huge blast ripped open the sky in a region of Siberia called Tunguska.  It flattened more than 2,000 square kilometres of forest all around.  

Eyewitnesses said that they saw this huge object tearing through the atmosphere and then exploding, as it turned out probably a few kilometres above the ground. It's estimated that this explosion was the equivalent of about 3 to 5 megatons of TNT. That's 5 times more powerful than the biggest US nuclear weapon.

Obviously, the leading theory for this is that something came from space - a chunk of asteroid or perhaps a comet and broke up on entry. But the trouble is, scientists have never actually found any residues. There's no fragments been recovered despite the fact that there's many scientific expeditions, and that's left the way open for lots of speculation about other possible causes - anti-matter, black holes, aliens, all sorts of things. I think it's even featured in an episode of the X Files. What's happened now is that a group led by Ukrainian scientist called Victor Kvasnytsya has identified very small fragments of rock, less than a millimetre wide each that look very much like they came from a meteor. They're in the right layers of peat which would date them exactly the right time that the explosion happened. These looked like our strongest candidates ever of rock from that explosion.

Kate - I actually gave this a bit of a Google before we had a chat and there are pictures on there of thousands and thousands of trees just sort of lying down on their sides. If we think it's such a massive collision, why haven't we found a large number of rocks?  Why are we only finding these tiny fragments?

Mark - Well, that's the thing. What happens if you have something coming space that was basically an iron-based asteroid then it will be dense enough to survive this fall through the Earth's atmosphere and you would expect to find large chunks actually of iron strewn around the region. You'd also expect to see a massive crater like the huge crater in Arizona for example.  

What scientists think with the Tunguska event was that, it was a more fragile body basically. It wasn't as dense. It wasn't as strong and that's why it broke up. And when it broke up in this huge explosion, it just would've almost vaporised all the material into tiny, tiny fragments.

Now, previous expeditions have found hundreds of what they call 'black magnetic spherules', tiny balls of material basically in soils, but they've never really been unequivocally proved to be part of the Tunguska meteor. These fragments in contrast because they're bigger, you can get an awful lot more information out of them. They've got a form of carbon in them called lonsdaleite and that's got a crystal structure - so, halfway between graphite and diamonds. Only forms under extreme heat and pressure, and you do often find it in meteorites. They've also found iron based minerals, one of them, an iron-nickel alloy, that's veined through the carbon and it's in proportions in a composition that's very, very similar to that of other iron rich meteorites.

Kate - Is this comprehensive though? Are all asteroids the same? Is there a certain signature that we can say that definitely comes from a meteor?

Mark - Well, there's one thing that doesn't fit which is why there's still going to be debate about this. Almost all meteorites tend to have very high levels of quite rare metals called iridium and osmium which on the Earth, all tends to be deep below the Earth's crust. You don't find much of it on the surface. So, where you find high concentrations of it, very often, they have come from objects from space. These samples have got levels of iridium and osmium that's halfway between what you'd expect to find in terrestrial rocks and what you'd expect to find in space rocks. So, there's some uncertainty about that. The team are now going back to do further isotope tests to try and determine that extra-terrestrial origin.

Kate - But until that happens, I suppose the conspiracies will continue.

Mark - They're certainly fun. So, I'm sure they will.

A 24-year-old leper, photographed in Sweden in 1886

14:08 - Leprosy DNA from Mediaeval Skeletons

German scientists have used DNA from ancient skeletons to rebuild the genetic sequence of mediaeval leprosy...

Leprosy DNA from Mediaeval Skeletons

German scientists have used DNA from ancient skeletons to rebuild the genetic sequence of leprosy skullmediaeval leprosy.

Caused by Mycobacterium leprae, leprosy was at one time a worldwide scourge affecting millions. But for reasons scientists don't understand, the disease abruptly disappeared from Europe during the 16th Century and nowadays is found only in the third world where it causes about 200,000 cases of the disease per year.

Victims are thought to pick up the infection by breathing in airborne droplets laden with the leprosy bacteria which have been coughed out by infected individuals.

Contrary to folklore, the disease doesn't cause parts of the body to drop off, but it does attack nerves, causing sensory problems, and growth of the bacteria in the skin and nasal passages can cause disfiguring changes to a victim's appearance.

Leprosy also damages the skeleton, leaving characteristic changes in bones, and it was from 5 skeletons bearing these hallmarks that Tubingen University researcher Johannes Krause and his team extracted DNA and successfully decoded the genetic sequences of the leprosy that had ravaged these individuals more than 600 years ago.

Incredibly, the level of bacterial DNA preservation was outstanding, enabling the scientists to assemble a complete genome map for the organism.

The team put this down to the fact that the leprosy mycobacteria have a tough, waxy cell wall, which can act as microscopic time capsule, preserving the DNA inside. But most surprising of all is that when the team matched up the leprosy sequences from their skeletons with the DNA code of modern leprosy strains still circulating, they were almost identical.

This proves that leprosy didn't disappear after the middle ages owing to some dramatic change in the bactierum itself, the researchers argue in their paper in Science.

Instead, they say, some other factor must be responsible, such as the disappearance of another - as yet unknown - pathogen that made people more susceptible to the disease; or perhaps living standards, nutrition or overall health improved, making the population less susceptible and pushing out the bug.

Rusting Steel in Concrete. Picture taken in Hippodroom Oostende.

16:51 - Self-healing concrete

Engineers and biologists are working together to produce bacteria capable of repairing concrete...

Self-healing concrete

Rusting Steel in Concrete.A £3 million grant has been awarded to teams across Bath, Cardiff and Cambridge universities to investigate a new building technology; self-healing concrete.

Concrete is vitally important for the structural integrity of buildings and foundations and while we might think of it as a long lasting material, over time, tiny little cracks can form which can weaken it.

These cracks let in water, which can freeze and widen the crack through to the steel frame which re-enforces large blocks of concrete. When that steel frame gets corroded, it stops the tension that pulls all the concrete together, weakening it. Repairing this concrete can be costly, but cement production produces around 7% of the world's CO2 production. So, if we can reduce the amount of concrete that we need to repair or replace we can not only save money but also reduce our overall CO2 emissions. 

The idea these teams have come up with is to allow concrete to repair itself by impregnating the liquid concrete with thousands of microcapsules containing bacteria. These bacteria produce calcite, a crystal version of calcium carbonate. So when a crack forms and the microcapsule is broken open, the calcite produced would not only block up the crack to prevent water from getting in but also use up the oxygen in the crack which would stop the metal frame from corroding. 

There are several hurdles to overcome, firstly designing microcapsules which are able to withstand a huge amount of pressure within the concrete but crack open when exposed to water as a crack forms. The bacteria also have to be carefully selected as they have to survive the alkaline conditions of the concrete and survive for potentially hundreds of years. The team are are beginning by selecting bacteria from soda lakes which are used to conditions which a high pH and have decided to use bacteria which produce inert internal spores (similar to although certainly not including anthrax). This way when the capsule is broken open by a crack water can activate the germination of the inert bacteria which will naturally start producing the material to plug up the gap!


20:28 - Do tobacco adverts influence teenagers?

A new research study investigates whether teenagers exposure to tobacco adverts can predict their smoking habits.

Do tobacco adverts influence teenagers?
with Matthis Morgenstern, Institue for Therapy and Health Research, Kiel

The more tobacco adverts a teenager sees, the more likely they are to become an addicted smoker, new research has shown.

It might sound obvious, and the mere fact that industries including tobacco companies, spend billions on promotion suggests that it pays to advertise, but the tobacco industry has repeatedly denied targeting teenagers in pro-smoking campaigns, with individual companies arguing instead that they are merely seeking to increase their market share among adult tobacco consumers.

Now Matthis Morganstern, from the Institute for Therapy and Health Research in Kiel, Germany, has produced the most damning evidence yet that, regardless of who the tobacco industry say they are targeting, their adverts appear to be triggering teens to take up the habit.

Writing in the journal BMJ Open, the German team followed up during a 30 month period over 1300 - initially non-smoking - adolescents recruited from 29 schools.

At the start of the study, the students were asked if they recalled seeing, and how frequently, images of adverts used recently by tobacco companies.

Advertisements for neutral products like confectionary, gadgets and clothes were also included as controls.

The researchers then re-questioned the participants 30 months later to examine their smoking habits. Since being recruited, 33% had tried smoking, 10% had smoked in the preceding 30 days, 5% reported smoking more than 100 cigarettes and 5% reported being regular, daily smokers.

Plotting these smoking habits against the numbers of self-reported contacts with tobacco advertising, and controlling for social and other factors, the team found a highly significant association.

For every 10 tobacco-ad contacts reported, there was a 38% increase in the likelihood of an individual subsequently taking up smoking.

This, Morganstern emphasises, is strong evidence that tobacco promotion is associated with teenagers taking up the habit "and it should be banned outright."

Rolled tongue

Why do we wet a finger to turn pages?

Chris - You know, a lot of people don't like that finger-licking business with pages because of the potential for... 

Kate - It's the horrible noise!

Chris - Well, that and the germ transmission!

I was thinking about this, why should a wet floor be slippery while a finger that's licked and then applied to a piece of paper should enable you to get a better grip? The wet floor is quite simple to explain, because there you've got a lubricant - a liquid - between the sole of your shoe and the floor. Therefore, the friction will be lower, and therefore, when you push against the floor to try and walk, you're more likely to slip.

But, if you lick your finger, you're putting a film of water over the end of your finger. If you then apply that to the page, you're going to squeeze air out from under your finger between your finger and the page, and the water has a thin film around the edge and is going to prevent the air getting back in, so there's going to be effectively a vacuum - or at least a partial vacuum - between your finger and the page surface, at least for a little while, and that's going to help you get a better grip, I think...

Everest Trek - Lukla

28:51 - What can mountaineers teach doctors?

Intensive care units are looking to mountaineers to learn how to improve oxygen uptake in their patients.

What can mountaineers teach doctors?
with Dan Martin, University College London

Extreme sports fans have always tested themselves to the limits, but now, an Mount Everestunderstanding of how our bodies react to extreme environments is helping medical professionals treat critical patients in intensive care. We were joined by Dan Martin from the Centre of Altitude and Extreme Environment Medicine at University College London.

Kate - You climbed to the summit of the highest mountain in the world, Mt. Everest in 2007 as part of the Xtreme Everest Project. What can we do on that mountain that can give us an insight into how our bodies change at altitude?

Dan - Well, the purpose of going there in 2007 was to look at how volunteers adapted to the very low levels of oxygen, not only going up the mountain, but also coming to base camp where we had a big laboratory set up. We wanted to see if we could pick out physiological mechanisms that would determine who would do well and who would do less well at altitude, and perhaps this would allow us to understand more about a similar situation which is patients on intensive care units who, pretty much all of them, at some point in time during their stay on the intensive care unit are exposed to very similar levels of oxygen in their bloodstream.

Kate - Now, while you were on your way back down from the summit, you actually drew your own blood and came up with the lowest amount of blood oxygen ever recorded. How did it feel to get that record at that time?

Dan - At that time, we obviously didn't realise how low the numbers were. A little group of us stopped just below the summit and the weather was not precisely what we wanted it to be on the day as weather is from time to time. It was a little bit too windy to strip off and expose ourselves, because you have to take the blood from an artery in your groin, so you have to take off those big down suits that you see people wearing on the summit of Everest. So, we dropped down a little bit, made a little shelter, took the blood from each other and then rushed the samples down the mountain. It was only much later in the day when we saw the figures from our laboratory where it was processed and we were really quite surprised at just how low those figures were.

Kate - Were you wearing oxygen mask at that time because I know a lot of climbers wear those to get to the summit of Everest? Would that have affected your blood oxygen level?

Dan - So, we did climb with oxygen and we certainly summited wearing oxygen because we felt it to be safer that way. But when we came down to the shelter where we took the samples, we took the oxygen off and then sat and rested for about 20 minutes, half an hour, to ensure that the oxygen had flushed out of our bloodstream and then we took the samples.

Kate - You were talking a little bit earlier about how different people physiologically react to the altitude. If you had the lowest amount, does that mean that you reacted worse to other people and why might that be?

Dan - What it may demonstrate is that me and probably lots of other people, it's just that they haven't been tested, have an amazing ability to adapt to these very low levels of oxygen and actually, whether your blood level is high or low may not be relevant at all. It's the adaptive processes that are going on underneath which we're really interested in.

Kate - It's not just about the amount of oxygen in our blood though as you just mentioned. It's also about how it reaches our tissues. How does that change at altitude? How do we know how much oxygen is actually getting to our tissues and how effective that system is coping with the altitude?

Dan - In 2007, we looked at a lot of processes which govern what we call 'oxygen delivery'. So, how much oxygen leaves your lungs and your heart and is pushed around your circulatory system to the tissues which require it. And what's interesting from what we found is that there's barely any difference between the people who do well and the people who do less well, with the amount of oxygen that's delivered. That also mirrors what we see on intensive care units, so, what we're really focusing on now is how the oxygen is delivered on a microscopic scale within something called your microcirculation - the very tiny blood vessels which pass through all your tissues and organs. And even further than that, how the tissues and cells use that oxygen so the mitochondria in the tissues and how they respond differently in different people.

Kate - We're all familiar with that Casualty image of the oxygen mask over patients' faces though I suppose and that's a little bit similar to the climbing mask that you wear. If we're looking at oxygen on a micro level, is that oxygen mask that we imagine in intensive care, how do we know that that's helping in the right way?

Dan - Well, it may not be helping and that's part of the strategy that we're looking into. Oxygen is very harmful. It's a toxic substance and given in high concentrations, it's very damaging to the tissues in your body. So, what we're striving to find is an alternative way to treat people who've got low levels of oxygen and that may involve using drugs and strategies to alter what's happening at a cellular level. We know that the mitochondria behave very differently when they're exposed to low levels of oxygen for prolonged amount of time and it may be that we can alter the way in which they work eventually, using some sort of medication.

Kate - When you go to Everest, you go up the stages of altitude quite slowly to avoid altitude sickness, amd over time, your body becomes acclimatises to the low levels of oxygen that you mentioned a little bit earlier. When we go into an intensive care ward and that person has low levels of oxygen, they haven't had time to acclimatise to it. Is the idea of trying to work out how we can get intensive care patients to bring on that more effective system of handling low oxygen levels?

Dan - Yes, absolutely. What we're not trying to do is to look at the very acute injuries that people may have. So, they have a road traffic accident for example and are brought into the accident and emergency department, that's a very acute change in the amount of oxygen in their blood, and those people most definitely need oxygen to get them through that. But as you get slowly sicker, and sicker, and we look after patients on the intensive care unit for weeks and month on end, they will produce the same sort of adaptations that climbers produce as they're climbing big mountains. And we may be able to alter the way in which that happens for the people who are not doing it very well, such that their cells and microcirculation may work better in low levels of oxygen.

Kate - Can we encourage those adaptations to take place?

Dan - We certainly may be able to. We are looking at a substance called nitric oxide which is a naturally occurring substance in the body which helps to control the microcirculation and also to alter how the mitochondria work under different circumstances and we've already looked at a previous experiment when we went to the Alps in 2010 at altering the amount of nitric oxide in your body to see if it will alter cellular processes when you're exposed to low levels of oxygen.

Kate - We're still doing these trips to Everest and these trips to other mountainous areas. What are the next experiments that we can do up there to further our knowledge of low oxygen levels?

Dan - We have no plans to return in the near future, but another strategy that we use and we've been working with our colleagues in the United States at Duke University is they have a hypobaric chamber set up and in the chambers, it's a far safer environment than perhaps being at the top of Everest. So, we can do fairly invasive and very focused studies on small groups of people. So, I think that's perhaps where we will take our work next to look at some very detailed studies in the future.

Kate - And how does that hypobaric chamber work? Does that change pressure levels?

Dan - Yes, it does. So, it simulates high altitude. It's the opposite if you like to a hyperbaric chamber that people are more familiar with that treats divers with decompression illness. In this chamber, the pressure is reduced rather than increased. So, it's as if you were ascending to high altitude, but what it does mean is that you can have a very safe set up inside and you can get people out quickly if there are problems during experiments.

A freediver with a monofin

36:28 - Freediving on a single breath

How does 'lung packing' help professional freedivers prepare for the low oxygen and high pressure enviroment they dive into?

Freediving on a single breath
with Peter Lindholm, Karolinska Institute, Sweden

Free-divers face low oxygen and high pressure enviroments as they dive to A freedivergreat depths on one lungful of air. We spoke to Peter Lindholm from the Karolinska Institute in Sweden to find out more about the physiology of achieving this. 

Chris - So, when people do professional free-diving, how deep do they go and how long do they have to hold their breath for?

Peter - The competitive divers, they can hold their breath and swim for something like 4 to 5 minutes which gives them an opportunity to swim down to about 100 meters using their swimming trunks basically. No fins, no nothing. But if they use a monofin, the record today is about 25 meters deeper. If you compare that, that's 250 meters which is about 5 lengths in the big Olympic swimming pool. So, it's quite significant.

Chris - Stupendous depth, isn't it? What will they do before they go down to that depth to prepare themselves physiologically?

Peter - First, they train for a few years. You must take that into account; they are good swimmers, and they have adapted their body to breath holding in some extent and they also have a good stamina, good physical shape. But if you're looking at what they're actually doing on the day, they would prepare most likely with not eating a lot. You don't want to be too full. Then they prepare by warming up with a few breath holds, shorter breath holds to get into the warm up phase then they hyperventilate. They usually hyperventilate for a few minutes, reducing the CO2, the carbon dioxide stores in their body, and also, topping up a little more oxygen in their lungs and in their venous blood.  So, they actually maximize the amount of oxygen stores they could carry for this dive and they severely reduce the carbon dioxide stores which has a few other implications. And then before they go down, they use something they call lung packing which I call glossopharyngeal insufflation or glossopharyngeal breathing where they actually swallow air into the lungs. You can learn this manoeuvre and you swallow air into your lungs and you can now actually pack this air down, and the best divers pack 50% extra air into their lungs compared to what their full lung volume would be without this technique.

Chris - Does that not have a consequence for, it makes them a lot more buoyant?

Peter - Yes, so depending on what depth you're looking at. If you're looking at a shallow dive, you know, snorkelling around in 5 to 10 meters, you don't want to be too buoyant. But if you're going for 100 meters or deeper, they use a lead weight. So, they usually buoyant themselves so that somewhere half down, they actually become negatively buoyant, so they actually can sink down to the bottom. And then they have to swim up and they're very heavy because the air is compressed at depth, so they actually become very heavy. And when you swim up, it's tough swim in the beginning but air will then expand, and it will give them great buoyancy in the end. The buoyancy at the end is a safety factor. It's good to be buoyant if you're tired or if something happens, you want to pop up.

Chris - Can we just return to the point you made about carbon dioxide first because you said there were some other manifestations in the body - when a person hyperventilates, they feel quite giddy. Is that sensible when you're going to be diving to more than 300 feet underwater?

Peter - If you hyperventilate regularly like the divers do when they prepare for these dives, the brain adapts somehow, so they're not so giddy. But there are some other problems and actually, they can get giddy at depth because of nitronarcosis, but that's another issue. If you had anything more about the carbon dioxide, it comes with a certain risk too because if you do this, you might not have the problem of being giddy if you are used to it, but it takes out the respiratory drive, so you might not feel the same urge to breathe as you would, holding your breath normally.

Chris - And this of course means you may not notice that you're becoming extremely low in oxygen and you may not know when is the right time to surface.

Peter - Exactly. If you swim to 100 meters, you need to swim another 100 meters up. So, if you would just continue, continue down and not look to get up, you would probably reach 200 meters, right? So, the divers have to decide to turn, not depending on the carbon dioxide signal or their respiratory drive, or their urge to breathe. They have to decide that, yesterday or last week, I made 99 meters, I came up, I felt good, I feel strong today. I'll try 100 meters.

Chris - And at those stupendous depths and therefore, pressures because every 10 meters of water is 10 times atmospheric pressure, isn't it? So, that's a huge amount of pressure. This will significantly squeeze the volume of air in the lungs down. Does this mean more oxygen is going to dissolve in the blood?

Peter - Yes. You actually can squeeze out more oxygen from the little there is in the lungs, but you'll have to sort of survive coming up because you have to pay that back when you go up. So, the last 10 meters before you surface, the pressure will reduce very quickly and if you have squeezed out too much of your oxygen, there is not enough left in the lungs to make you to the surface. So, you could actually have a situation where you have put out too much oxygen into your body. You still have oxygen in that blood in their muscle, but the brain doesn't get enough oxygen during those last seconds of the surfacing.

Chris - If we look around the world, we haven't always had competitive Olympic free-divers, but we have had people who have in certain cultures and civilisations become very good at diving very deep for very long times. I'm thinking of pearl divers and things like that. Are some people very good at doing this genetically?

Peter - There's still research to be done if we're going to decide how much is genetics and how much is training, but there are a few traits that makes you a better diver. The first I would say is big lungs and people are different. Some people have actually bigger lungs to their body size than others, so that's one. 

Another trait is something we called a diving response. It's an ability to, when you hold your breath, reduce the heart rate and that also depends on your ability to vasoconstrict to limit the blood flow going to your limbs. What this means is that the body has an ability to reduce or limit the blood that flows to your, not so important parts. Depends what you mean by important, but in terms of oxygen supply, your muscles or bones, or other skin structure, they can survive for at least half an hour without oxygen, the brain cannot. So the body will save some or conserve some of the oxygen in the lungs to be used by the brain during this dive. This diving response, the ability to vasoconstrict the vessels and reduce the heart rate, varies a lot between individuals. So, that would be two traits which both have some potential to be trained, but I think personally from the data I've collected and seen, I think a bigger component is genetic than the training component in this.

A man having an ice bath

45:00 - Diving into cold water

Heather Lunt tells us how the human body shuts down when immersed in extremely cold water...

Diving into cold water
with Heather Lunt, University of Portsmouth

Elsewhere we've talked about some of the challenges of free-diving, the lack ofA man having an ice bath air, the pressure, but I think my first problem would be that the water is just far too cold. We spoke to Heather Lunt from the University of Portsmouth who investigates how the body responds to immersion in extremely cold water.

Kate - So Heather, I at primary school used to have to swim in an open air swimming pool. It had no heating and I was regularly hoicked out of my swimming lessons because I just turned blue in the face. So, what happens to people like me who get put in incredibly cold water?

Heather - Well firstly, when you go into cold water, you can expect that you'll have this large gasp, followed by very fast breathing, uncontrollably fast breathing, so you can't talk and a really high heart rate. Now, we call this the cold shock response and this is what happens in the first couple of minutes of being in cold water.

Kate - And I suppose that's not very helpful. As you gasp, all that cold water is going to be able to rush into your lungs. Is that something you can learn to control?

Heather - Well, it's something that we can habituate to, we can get used to, by repeated immersion in cold water. But really, the idea is that we should where possible, enter water slowly so that we reduce this cold shock response and another advice sounds a bit pedantic when you're on dry land, but try not to panic and just keep your airway above the water level.

Kate - In a longer term when you're stuck in the water after that initial shock, what happens then?

Heather - You've got over this cold shock response. It takes 2 to 3 minutes for your breathing to calm down. We start to see a gradual cooling of the body. It takes between 3 to 30 minutes and it's really dependent on a large number of factors such as the water temperature that you're in, the amount of body fat that you have as well, and also, you get what we call a cooling of the nerves and muscles. And so, you start to lack the ability to move your fingers and toes in a coordinated fashion.

Kate - What do we mean when we talk about extremely cold water? How cold were you talking that it starts to become dangerous and we start to lose this feeling and our ability to keep afloat?

Heather - When we talk about cold water, we're talking from normal sea temperatures. Around the UK, standard sea temperature in summer would be between 15, 16, 17 degrees. We class that as cold, but we often see swimmers going into open water pools, into lidos at much lower temperatures.

Kate - I personally swim in lidos and I can guarantee that it is personally freezing, and I find a lot harder to swim outside in those cold temperatures. At what point does it become dangerous and affects our ability to swim?

Heather - We regulate our body temperature around 37 degrees Celsius and we will vigorously defend that. We have what's called - we term it clinically low deep body temperature at around 35 degrees Celsius. But long before we reach that low body temperature, the muscles and nerves of the arms will start to cool to the point where we're not able to coordinate action to swim. We then start to lose our coherence and gradually, as we cool to around 30 degrees, we become unconscious. And after that point, death will ensue.

Chris - What about some people who are more vulnerable to being cold than others? If I go in a swimming pool, I usually last about 20 minutes max whereas my wife, my daughter, who is tiny compared with me, they can spend all day in there. Are there some people who are more vulnerable to being cold immersed than others?

Heather - Certainly, body fat is an indicator. The insulative layers that you have will reduce the rate at which you cool. Also, the amount of exercise that you're undertaking, it may be that you may stand at the side of the pool and your daughter is very active in the water so, producing a large amount of heat to offset that cooling that's occurring despite her large surface area to volume ratio.

Kate - And does anything else affect that apart from body fat? Mine is particular high, but what can we learn about how we protect ourselves within the water?

Heather - If we know we're going into water, we can make sure we're wearing a life jacket or buoyancy aid. We can make sure that we don't thrash around too much, air trapped in the layers of our clothing will add buoyancy and also, what we need to do is once we've got over the cold shock response, we know that our fingers will start to cool rapidly within the first 30 minutes or so. And so, we need to think about our exit strategy early before we start to lose the ability to use our fingers and hands in a coordinated fashion.

Chris - So, if you are dumped in cold water, is it better to try to swim to stay warm or is it better to stay still and get a sort of bubble of warm-ish water around you, so you lose heat less quickly?

Heather - That's a million dollar question and that on-going in terms of research. I'm going to sit on the fance here. It really depends on the situation you're in, the water temperature, and also, your ability to actually swim to a point of safety, and raise the alarm. So, I'm going to sit on the fence here because there are so many factors involved that it has to be a coherent decision which is made, depending on the situation you're in.

Kate - You also trained I think Helen Skelton who did her experiment cycling to the south pole.

Heather - Yes, we did. That was a fantastic day, teaching her about - not only about the risk of having a cold deep body temperature, but also the effects of cold air, and how they can cause non-freezing cold injury - a condition of the nerves but also, how it can cause frost bite.

Kate - How do you go about investigating this? You're based down in Portsmouth. I presume you don't just take people out into the sea and dump them in when you're ready.

Heather - We have well setup labs down here where we have ability to put people into cold water and a range of safety criterias so that we ensure that we don't get people dangerously cold. So, we have, not only a cold water tank and immersion facility, but also a cold air chamber as well.

Chris - When I used to sit in lectures at medical school, I remember one person saying that there are some people who can swim in the Barents Sea, no problem. There are others that are far less resilient. And there was something special about those individuals. They didn't open up their blood vessels again when they got very, very, very cold because there is this paradoxical - you let loads of blood flow into your tissue when you get very cold, don't you?

Heather - Yes, we do have what's called a hunting response. So, we have investigated this to some extent where we find that when the tissues become very cold, particularly in the fingers, we find that arterial blood vessels are paralysed and the blood vessels are gradually opened and so, it release blood back into the tissues, rewarming the tissues of the hand. But then once the hand is warmed slightly, this then means that the muscles around the arterials are able to contract again, causing that reduced blood flow again. It's supposed to be a protective mechanism to prevent local damage to the tissues occurring from being too cold.

Kate - We've been talking about applications to a medical sense from what we're learning about this extreme environment as well as understanding how we can save ourselves if we accidentally find ourselves in a very cold water environment. How else can we apply this?

Heather - Well, there's recent evidence within the medical literature which I'm by no means an expert in, but they've shown that selective brain cooling can help with survival through operations. So, making people cold slows down the rate at which the cells of the body use oxygen and so, buys them time that certain operations can be undertaken and they have fewer problems upon recovery from their operation by making their deep body cooler.

A crying toddler

The physiology of crying?

Hannah - So, what is going on in our bodies and brains during an emotional breakdown? And why is it that sometimes we can have such strong emotional reactions to things?

Joe - Hi. I'm Joe Herbert and I work in clinical neuroscience at Cambridge. So, why do emotions take over? Well, they take over because they're so important. Because it ensures the things that are good for you, arouse positive or pleasurable emotions and are therefore preferred. Whereas the opposite applies to things that are bad for you which give rise to negative emotions. But secondly, it acts as a vital part of social communication. It recruits others to help you or join recognizing emotions in others is an essential ingredient of good social relationships.

Hannah - And are there specific hormones or parts of the body involved in such emotional responses?

Joe - Your whole body takes part in emotions including two rather special hormones - adrenaline, which Americans call epinephrine surges out when you're frightened or excited, and makes your heart beat faster, and your breathing become deeper.

Your brain has adrenaline surge of its own and this makes you alert and pay attention.

If your emotion runs hard for much longer, a second hormone, cortisol joins in particularly if emotional experience is stressful. Cortisol sensitises your brain to unpleasant events and makes you remember them better. So, you avoid the situation that brings them about.

We don't yet know whether the brain has special chemicals that signal fear or happiness or anger, and so on, but it's possible they may exist.

Hannah - Thanks, Joe. So, strong emotional reactions are there to help us to communicate our feelings with others and also, to help us remember that particular situations should be avoided in the future.


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