#242      30 min 03 sec
Peak performance: Should elite athletes train at high altitudes?

Exercise physiologist Prof Jerome Dempsey discusses how the human body responds to lower oxygen concentrations at high altitudes and whether elite athletes really benefit from training under such conditions. Presented by Dr Shane Huntington.

"So the problem was living and training at high altitude is you may gain something with haemoglobin but you lose something. You can't train your muscles as hard." -- Prof Jerome Dempsey




Prof Jerome Dempsey
Prof Jerome Dempsey

Jerome Dempsey is the director of the John Rankin Laboratory of Pulmonary Medicine at the University of Wisconsin-Madison. His primary appointment is in the Department of Population Health Sciences, and he also holds affiliate appointments in Physiology and Kinesiology. His research interests are concerned with the regulation of breathing in various physiologic states in un-anesthetized humans and animals. One group of projects seeks to determine the limits of the healthy human pulmonary system for gas transport, respiratory muscle function and ventilatory output during exercise. The effects of aging, gender, fitness and airway reactivity on these processes are emphasized. A second major aim is the influence of respiration on  autonomic control of cardiovascular function. A third series of studies is concerned with regulation of breathing in waking and sleeping humans and animals, with specific emphasis on sleep apnea and the effects of novel treatments.

Credits

Host: Dr Shane Huntington
Producers: Eric van Bemmel, Kelvin Param, Dr Dyani Lewis
Audio Engineer: Gavin Nebauer
Voiceover: Nerissa Hannink
Series Creators: Kelvin Param & Eric van Bemmel

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VOICEOVER 
Welcome to Up Close, the research talk show from the University of Melbourne, Australia. 

SHANE HUNTINGTON 
I’m Shane Huntington. Thanks for joining us. The human body has evolved over hundreds of thousands of years to be optimised essentially at sea level. The amount of oxygen in the atmosphere at this level is very specific and our bodies seem to work best under these conditions. As we move to higher altitudes we fare poorly by comparison. In the past, these considerations were most pertinent to mountain climbers and sightseers who ventured to where the air was thinner. Today however we see elite athletes choosing to train in low oxygen environments in the hopes that such conditioning might give them an advantage. But is this approach supported by evidence? To explore the way the human body reacts to altitude and whether there's an upside to low-oxygen training, we are joined today on Up Close by exercise physiologist Professor Jerry Dempsey, John Robert Sutton - Professor of Population Health Sciences and Emeritus Director John Rankin Laboratory of Pulmonary Medicine at the University of Wisconsin, Madison. Professor Dempsey is here at the University of Melbourne on a Miegunyah Fellowship. Welcome to Up Close Jerry.

JEROME DEMPSEY
Thank you very much.

SHANE HUNTINGTON
You work specifically in the area of hypoxia. Can you give us an understanding of what hypoxia is and what it does to the body?

JEROME DEMPSEY
Oxygen is delivered to the tissues of the body proportion to the amount of oxygen carried in the bloodstream and the blood flow, so it's that product that is key in providing sufficient oxygen. If either the amount of oxygen in the blood is below normal - and that can occur because lung function is abnormal or because you don't have enough haemoglobin, the main oxygen-carrying molecule for oxygen - or it can occur because you have insufficient blood flow because your heart doesn't put out enough or because you are not delivering tit o be appropriate to tissue - either one of those deficiencies can cause insufficient oxygen transport.

SHANE HUNTINGTON
Now let's say for example I'm travelling and I head up into the mountains and there is a change in atmospheric pressure. What sort of symptoms would I be experiencing if I was there just for a few days?

JEROME DEMPSEY
Well, first of all it should be clear that we can actually go fairly high before we experience - healthy people experience symptoms. And this is because of our wonderful characteristic of haemoglobin that even though the pressure of oxygen is falling in the air and in our blood, the haemoglobin holds tightly to oxygen until the oxygen falls about 30 per cent below normal. So you can fly in a pressurised jet for example, at 8000 feet - or 2500 metres - and you don't even know you're hypoxic at all. So this is a wonderful adaptation. This is something that doesn't have to be called into effect, like a faster heartbeat or breathing more, it's there all the time. As far as I know its cost is zero. So there's no downside to that sort of adaptation, it's there all the time.But once you get above, in healthy people, 2900 metres, 3000 metres, then you are now at a stage where haemoglobin starts to lose its oxygen and this is serious hypoxia after that. The symptoms that you feel, well there are many. First of all if you are there overnight you'll experience things like a headache that just won't go away with treatment, fatigue, very poor sleep, rapid heartbeat. You'll be aware of your breathing, which we're really aware of near sea level and things like your ability to move around, exercise is greatly hindered. So those are some of the major symptoms that you get.

SHANE HUNTINGTON
What's the limiting factor for us in those situations? Is it the actual pressure that we're experiencing that our lungs are having to work against or is it the amount of oxygen available to us within that pressure envelope?

JEROME DEMPSEY
The latter, it's the amount of oxygen available to us.

SHANE HUNTINGTON
So how low could we go in terms of pressure before we start having problems?

JEROME DEMPSEY
Well the atmospheric pressure you mean? Well, the normal barometric pressure here near sea level is about 760 millimetres of mercury - 740 to 760 depending on the weather. The pressure - if you go below 500 millimetres of mercury that's serious hypoxia. But, you know, the more physicians that I talk to who live at and have their practice at 2800-2700 metres, and a lot of middle-aged people or people in their 50s, are moving to places like Colorado in the US. One physician informed me just a couple weeks ago that now there's over 50,000 people just in Colorado that live between 2900 metres and 3200 metres altitude - that's such a gorgeous place to live - and he's seeing all kinds of problems with people. Maybe if there are comorbidities such as just normal ageing, this can impact that and you don't have to really go that high. If you're an athlete, if you go 1000 metres above sea level your performance is affected. It's less.

SHANE HUNTINGTON
Now many of the things you mention as symptoms are not things that are - ones we are aware of - or we might become aware of them but there are changes to the body that are happening involuntarily. How does the body sense that it's in this lower-oxygen environment? 

JEROME DEMPSEY
Well, we have a number of oxygen sensors in the body. The one that we know the most about is a sensor called the carotid chemoreceptor. The major vessels in your neck, just where they divide on the way to the brain, there's a very small receptor and it's called a chemical or chemoreceptor. There are many other sensors in the body that sense low oxygen. Like in the kidney, there are cells that sense low oxygen. They'll put out a hormone that eventually will produce small red cells by stimulating the bone marrow. So that's another kind of oxygen sensor. But this sensor I was just talking about, this so-called chemoreceptor, within a few seconds of becoming hypoxic, it will sense that, relay the message to the lower part of your brain and your breathing will increase, your heart will start to beat faster and you'll engage a part of the nervous system called a sympathetic nervous system that sends impulses out to all the blood vessels in the body and to the heart. So the heartbeat's stronger, which is good because if the oxygen is lower in your blood, you would like to compensate for that by increasing the blood flow. Unfortunately sometimes the response to the insult is worse than the adaptive side of it and that's what happens in hypoxia. There isn't such a thing as a perfect adaptation.

SHANE HUNTINGTON
You mentioned the heart, the lungs, the brain. Let's deal with the first two. Are the changes that occur when the person is hypoxic, they're just to the function or there are other changes going on to the heart and the lungs?

JEROME DEMPSEY
There are structural changes. We used to think that they took weeks, months, years. Now we know with entirely new methods that these changes start to occur in hours.  That is actual new protein being manufactured very very quickly, especially in that receptor I was just talking about. Its sensitivity doesn't stay the same. It starts to up-regulate, become more sensitive within hours of exposure to oxygen lack.

SHANE HUNTINGTON
Now you mentioned the brain as a result of the information being fed to it by that chemoreceptor changes the way our body reacts or changes our heart's function, our lungs' function. What about the brain itself? You mentioned headaches. What's happening in the brain as a result of oxygen deprivation?

JEROME DEMPSEY
Well that's - just the headache itself, we don't know exactly why that occurs but it's an example of the adaptation causing a problem. So the vessels in the brain, the blood vessels, if you decrease the amount of oxygen in the blood you'd like to increase the blood flow because it's a product of those two that's oxygen delivery, and that's what happens. The blood vessels, within seconds of becoming hypoxic, dilate, get bigger, so the blood flow to the brain increases. That's good from an oxygen-transport point-of-view. But the problem is that the human brain can't expand so the pressure inside the brain increases and many people think that's the cause of the headache that we get. The same thing occurs in the retina of the eye. Same thing, blood vessels expand, dilate, more blood flow. But blood flow to the retina as it increases causes retinal haemorrhage which is a very common thing above 3000 metres at high altitude. So that's just one of many many examples of how an adaptation has a negative side as well and that physiology has fascinated me since I was a graduate student, just that hypoxic is a very very complex insult and there's always the two sides to it.

SHANE HUNTINGTON
Jerry I've just finished my three or four days up in high-altitude environment. How long does it take for these effects to wear off in my body completely?

JEROME DEMPSEY
There are some effects that never wear off. Some of that early sickness, fatigue, sometimes you adapt to that, get used to it and some changes occur to help you with it, like the most common one people think of, this hormone that I talked about that the kidney secretes and we produce more red cells. Well that question's been looked at again very recently and it turns out that it takes a lot more hypoxia and a lot longer than we ever thought to produce more of these red cells but it's one of the helpful adaptations. But there are some things that occur that don't get less, they get worse the longer we stay. Two things I can mention, one is the activation of this so-called sympathetic nervous system, it just skyrockets. The longer we stay there, the more sensitive this little receptor gets, the more the sympathetic nervous system's engaged. That causes blood vessels to constrict, get narrower and causes hypertension. That's in the body, what we call systemic hypertension. The worst kind of hypertension is what occurs in the lung. I think this is the most serious one. Blood vessels in the lung, instead of dilating, getting bigger when they become hypoxic, they constrict, they go the other way. If you had just a part of your lung hypoxic, that would make sense because it would mean it would take the blood flow going to that part of the lung that isn't being oxygenated very well and send it to someplace [and oxygenate it]. But when you are on top of the mountain, all of your lung is hypoxic. So that's really bad. Pressures get very very high in the lung and the pressures can get so high that fluid moves from the vascular space into the gas exchange units. A lot of the fatalities that occur on a mountain are due to this so-called pulmonary oedema, fluid getting into the lung. It was a well-meaning adaptation but we should have gotten rid of it right after we were born but we don't, we hold on to that. That's one of the strong examples of why humans don't do well on hypoxia.

SHANE HUNTINGTON
I'm Shane Huntington and you're listening to Up Close. In this episode we're talking about hypoxia with exercise physiologist, Professor Jerry Dempsey. Jerry, there are a number of communities, for example the Tibetans that live in these high-altitude environments their entire lives. You've talked about many of the effects of hypoxia but do we see that in these communities where they're born, bred and have evolved over many tens of thousands of years in these environments?

JEROME DEMPSEY
Yeah, that's always been a fascinating study of people who were born and raised in those environments. And you can see some wonderful adaptations in there. For example the lung actually increases its size, that is its ability to exchange oxygen improves substantially in those people and that's a real plus. Plus this little receptor we were talking about loses sensitivity in those people. So the combination of those two things would seem to be really good. On the negative side of that, their vessels in the lungs still constrict. So the amount of hypertension in the lung that exists in high-altitude natives is a very very high prevalence - and remember that those people that have been studied are the ones that are still there. They're the survivors. There are many people who have left because of this. So that's a very serious sort of adaptation that doesn't occur. Another one is problems with reproduction. The most startling thing I ever read on that - but these were newcomers, from when the Spaniards invaded South America in the fifteenth century. This is historical recording, so you're never sure these are exactly true. But it's thought that the first 56 births were all stillbirths until finally one survived. It shows you the problems with reproduction. Now what about the natives of high altitude? You still see that they have low-birth weights, problems with pregnancy and the problem is the blood flow to the placenta is hindered in a hypoxic environment. So those people that are born and raised at high altitude in North America and in South America. The last 10 years the Tibetans have been studied in more detail. They've been at high altitude probably 30,000 years, much longer than others and it looks as though they might be different.So we might come as close as we can with those people in the true adapters. For example you don't see them producing a lot of red cells because see, you can produce too many, get the blood way to viscous and that happens with a lot of high-altitude natives. They don't tend to do that. They have a different genetic expression and even that's being explored now. It looks to be unique and in the reproductive side, it looks like that's even a little better. But I am not thoroughly convinced yet. I don't think the studies have been done on the lungs circulation and I'd like to see how the lung is adapting in these people, especially the degree of pulmonary hypertension. But it's certainly an exception to my bias in this that humans don't adapt. These ones just might.

SHANE HUNTINGTON
You've described in some detail what happens to everyone else on the globe when they go the higher altitudes, what symptoms they feel. When you bring the Tibetans down to higher-oxygen environment, what sort of symptoms do they display?

JEROME DEMPSEY
No problem.

SHANE HUNTINGTON
No problem at all?

JEROME DEMPSEY
Nobody that I know of has a problem coming to a 150-millimetres-of-mercury inspired air rather than 50. Everest is 50. We're in the 150 right now. Coming down, that's fine.

SHANE HUNTINGTON
Yet I don't recall seeing a large number of Tibetans in the Olympics for example, outperforming other athletes. Is there no advantage to them because of that?

JEROME DEMPSEY
Yes I don't recall seeing a lot of Tibetans doing it either. The whole idea on exercise performance, when you see the Kenyans, they do extremely well in the Olympics. We first found out about them at the Mexico City Olympics, the only Olympics to be held at the 7500-foot range, something like that. There we first saw the Kenyans and we first saw Mexican residents do well and that's where the champion sea-level residents did not do well at all. The one I remember the best is Australian Ron Clarke. This wonderful athlete held something like six distance world records. He could barely finish a race up there. He was really affected by the altitude, as were a number of other world record holders at the time. That's when we first said my gosh this isn't a severe altitude but for those athletes trying to do what they were doing, it is a very very severe altitude.

SHANE HUNTINGTON
With the Kenyans doing so well in some of these international events, do we have an understanding of what's giving them an advantage in these high-altitude environments?

JEROME DEMPSEY
Well a lot of people of course have been very intrigued with this and they are such wonderful endurance athletes and every year, every major marathon in the world, men and women, are won by these, and the Olympics of course, in all the endurance events they do very well. The theories I've heard go everywhere from the fact that they're high-altitude dwellers, that their cardiorespiratory system is developed structure-wise differently. But they haven't been studied that thoroughly. There are other theories that claim it's not their maximum ability to consume oxygen that's so different, it's the efficiency with which they run - the structure of their limbs, things like this have been brought up. It's a wide range of possibilities here. See, it doesn't take much. We're talking about differences of two and three and four per cent in performance that make the difference between not even being on the Olympic team and winning a gold medal. So these are difficult to sort out. But now the genetic side of things is starting to be looked at. And oh, we'll unravel this eventually.

SHANE HUNTINGTON
With regards to these high-altitude environments though, are there particular animals that have adapted much more effectively to this than humans have...

JEROME DEMPSEY
Oh yeah.

SHANE HUNTINGTON
...we see in Australia for example animals that haven't necessarily developed altitude enhancements but certainly have looked at the environment at higher altitude and been able to work more effectively. So we have something called the Mountain Pygmy Possum that only exist above a certain altitude because the ecosystem there is one in which it can be a major player. Do we see that with regards to altitude and so forth?

JEROME DEMPSEY
There are absolutely gorgeous examples of hypoxic-tolerant animals. My favourite one is the Bar-headed goose and this has been reported by people who have gotten to Everest and when they've looked around, they look up above 8500 metres and the geese flying in flocks to their mating grounds. Zoologists studied these animals. When I was in British Columbia a few months ago I saw one of these geese flying in a wind tunnel with a small mask on its face that they were delivering nitrogen to - nitrogen at zero oxygen. So they got the oxygen down to about 35 millimetres of mercury in the inspired air. That's well above Everest. The lower the oxygen got, the harder this animal worked and it was the most beautiful flight that you ever saw.So what's different about them? Well I'll just mention a couple of things. Everything that the human does we suspect is bad in hypoxia, they don't have. For example the vessels and their lungs don't constrict in a low-oxygen environment. So they'll never get pulmonary hypertension. Secondly their lung is not a dead-end sack like ours. Birds breathe through their lung into hollow bones so the air moves in a counter-current fashion. So they don't lose any oxygen from atmosphere to blood. That's really good. Other things like the blood flow to their brain increases but their brains can swell. So intracranial pressure does not go up. So those are just three of the things and there are many more - their flight muscles, the distribution of blood there. So they're ideal. But there are other ones, like there are relatives of the carp that can live in frozen lakes where there is zero oxygen in the environment but they don't hibernate. They forage around the food all winter long. Well they have a different metabolism. They make all kinds of lactic acids - a product of anaerobic metabolism - but they have an enzyme that can convert that to ethanol and it defuses out over their gills. So it's very special things like this. The human foetus is another one that lives in a hypoxic environment but its haemoglobin is adjusted so that it binds oxygen substantially better and as soon as we are born, within a few weeks that converts to an adult haemoglobin. So those are some very important adaptations and maybe the Tibetans headed a little bit in that direction.

SHANE HUNTINGTON
In this episode of Up Close we're talking about the effects of high altitudes on human body with exercise physiologist Professor Jerry Dempsey. I'm Shane Huntington. Jerry, as we know there has been a big push for particular athletes to try and gain performance advantages by training in these high-altitude environments. What's the reasoning behind this?

JEROME DEMPSEY
I think the first I remember research being done on this on athletes - was in preparation for this Mexico City Olympics because this was a complete unknown. They would take the athletes to high altitude and they would live there and train there. The idea was that you would live there and gain haemoglobin. There's no doubt that doping works. You normally have about 15 grams of haemoglobin. If we gain 1 gram of haemoglobin, that'll make a huge difference in performance. So there's no doubt about that. We also know that if you exercise in a hypoxic environment - such as train - you can't work as hard. If you don't have a normal oxygen transport to those muscles, you can't work as hard. So the problem was living and training at high altitude is you may gain something with haemoglobin but you lose something. You can't train your muscles as hard.So people were finding that when they came back down to sea level after this - really well-controlled experiments now not anecdotal stuff - that they were actually losing performance. They'd take biopsies - pieces of tissue from the muscle - and you could see the aerobic capacity, the number of mitochondria in the muscle was actually decreasing. So that wasn't the way to go. So in the '90s people started to do experiment with the idea of sleeping or living in a hypoxic environment, like a chamber - okay, a low-pressure chamber - but then getting out of that in the morning and training in a normal environment. This got rave reviews. People thought this was terrific. Well as studies started to be repeated and very carefully done, there were mixed results. You might find a small portion of the athletes improve their performance but the rest wouldn't. Some even got worse. Why is that? Well, it wasn't until last year that the first placebo-controlled study was done, which is quite amazing to me that 15 years or more of research on this and thousands of athletes doing this now. Australia's one of the world leaders I think in this but Europe and North America, they are all doing it. The first placebo-controlled study was negative. Oh a couple of athletes that are little better - and this is absolutely necessary going forward to look at it this way because if exercise performance is your major outcome that you're looking at from this, athletes, if they have an expectation, that's going to affect their performance. There is a lot above the neck just as much as below. So these have to be done.They are not being done. They're very difficult to do - to do properly. Even the one that was done could have been done a lot better - and actually I know the investigator that did it and he's working on it right now, trying a different way. So I think this needs to be examined. Here's my concern, that there may be a negative side to this. About half the research I've done over the past 35 years has been on sleep apnoea. When people have sleep apnoea they are not in a hypoxic environment of course, they are at sea level or near sea level. But the fact that their breathing stops sometimes 80-90 times an hour in severe sleep apnoea means that the oxygen saturation in their blood is rising and falling. This is the worst kind of hypoxemia - intermittent hypoxemia. This is very well known now. The blood vessels just can't handle this re-oxygenation swings that you see, especially when they're occurring that often.This carries over to the daytime. When you wake up, the sympathetic nervous system is turned on just like it was at high altitude but it stays on. So you have this high level of activity constricting blood vessels, you have all this inflammation occurring in these vessels, and the pulmonary circulation as well as the systemic circulation. Well, I guess people can say, but is that happening in these athletes, 25-year-old highly fit people? Well if they sleep high enough and if they're susceptible to unstable breathing - and a lot of people are - they will experience this. We know now, just in the past two years when this is now mimicked in healthy young men, even one week of doing this - eight hours a day - you can see increases in blood pressure, increases in the sympathetic activity we talked about, increases in inflammatory products.One might say oh but they're 25 years old, they're healthy people and there's no long-term effect really. Well I don't know that. I think - my proposal would be that people that are doing this, exposing these athletes, first should find out whether there really is a change in red cell mass - this is a lot harder to get than we thought both in terms of duration and the degree of hypoxia - and is the performance really changing, on the one hand. Secondly, what's the risk? Measure blood pressure, put a little oximeter on their finger when they're sleeping in these environments and see if they're some of those people that do get this intermittent hypoxemia because that is not good stuff, this intermittent stuff. So I think the pressure needs to be on the people advocating this and doing this to make sure this is a healthy and not unhealthy and that it works.

SHANE HUNTINGTON
Jerry, it's one thing to measure risk once they're in the environment and they're doing this. Do we have any idea of what risk factors there are before that? Is there anything we can do to look at these athletes and say well you're in a high-risk group, you definitely shouldn't even try?

JEROME DEMPSEY
Yeah or even is there a chance that you're going to increase your red cell mass? Again, if you do increase it, even 10 per cent, it'll help you performance-wise. It would be very difficult to screen, I think, young people with this but I can think of some things. For example, if they have a borderline blood pressure and they have a strong family history for it, I'd be very very careful of people like that. Other than that, I think it might be very difficult with young adults to screen them. If it's an obvious comorbidity - a problem with conduction in the heart, you'd have to be very careful about that - a lot of athletes have that problem actually as they develop with severe intense exercise over time. But that's one thing the people have been asking themselves, how can they predict - just the performance side now, not the negative side - but who's likely to increase and who isn't? The evidence that is coming out still needs a little more but those who already have a slightly-above-normal red cell mass amount of haemoglobin, they don't seem to do much in a hypoxic environment, at least this intermittent hypoxic environment. Whereas those that start low, they seem to be. So that might one thing explaining why some do well performance-wise and others don't.

SHANE HUNTINGTON
Professor Jerry Dempsey, John Robert Sutton - Professor of Population Health Sciences and the Emeritus Director of the John Rankin Laboratory of Pulmonary Medicine at the University of Wisconsin, Madison - thank you very much for being our guests today on Up Close today and talking to us about hypoxia.

JEROME DEMPSEY
I enjoyed it. Thank you.

SHANE HUNTINGTON
Relevant links, a full transcript and more info on this episode can be found on our website at upclose.unimelb.edu.au. Up Close is a production of the University of Melbourne Australia. This episode was recorded on 27 March 2013. Producers for this episode were Kelvin Param, Eric van Bemmel and Dyani Lewis. Audio engineering by Gavin Nebauer. Up Close is created by Eric van Bemmel and Kelvin Param. I'm Shane Huntington, until next time goodbye.

VOICEOVER 
You've been listening to Up Close. We are also on Twitter and Facebook. For more info visit upclose.unimelb.edu.au. Copyright 2013 the University of Melbourne.


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