Science Interviews

Interview

Thu, 13th Jun 2013

Diving into cold water

Heather Lunt, University of Portsmouth

Listen Now    Download as mp3 from the show Extreme Physiology: Everest to Ocean Floor

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.

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