Dan Martin, University College London
Extreme sports fans have always tested themselves to the limits, but now, an understanding 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 didnít 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, itís 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. Itís the adaptive processes that are going on underneath which weíre really interested in.
Kate - Itís not just about the amount of oxygen in our blood though as you just mentioned. Itís 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 Ďoxygen deliveryí. 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 thatís delivered. That also mirrors what we see on intensive care units, so, what weíre really focusing on now is how the oxygen is delivered on a microscopic scale within something called your microcirculation Ė 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 - Weíre all familiar with that Casualty image of the oxygen mask over patientsí faces though I suppose and thatís a little bit similar to the climbing mask that you wear. If weíre looking at oxygen on a micro level, is that oxygen mask that we imagine in intensive care, how do we know that thatís helping in the right way?
Dan - Well, it may not be helping and thatís part of the strategy that weíre looking into. Oxygen is very harmful. Itís a toxic substance and given in high concentrations, itís very damaging to the tissues in your body. So, what weíre striving to find is an alternative way to treat people whoíve 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 weíre 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, thatís 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 weíve 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 - Weíre 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 weíve been working with our colleagues in the United States at Duke University is they have a hypobaric chamber set up and in the chambers, itís 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 thatís 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. Itís 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, itís 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.