How flying affects you（在线收听）

　　Jackie:  Hello, this is Entertainment from BBC Learning English dot com withme, Jackie Dalton. I've just got back from my Christmas holidays,which involved taking a long flight. When I got off the plane, I feltexhausted and now I've got a cold and I've often wondered why flyingoften makes you so tired and run down. Today we're going to find out.
　　This programme is all about how flying affects your body. If you'veever flown, you may have noticed that when the plane takes off, yourbreathing becomes quicker and your pulse rate – the speed at whichyour heart is beating – goes up. This may partly be because you'reexcited or nervous, there's another reason. What is it? Listen toMichael Bagshaw professor of aviation medicine at Kings College,London, to find out.
　　MichaelAs you take off from sea level, there's quite a significant pressure change. The pulserate will go up very slightly so that you take in more oxygen and remove the excesscarbon dioxide from the system.
　　Jackie:  When you take off there's a pressure change so get as your body worksharder to get more oxygen, your breathing and pulse rate speed up.
　　Another thing about our breathing when we're flying is that the air in aplane is recycled - or reused – very often, which means you'rebreathing in a lot of other people's air. The ventilation – the movementof air – isn't great and lots of people are together in a small space. Thismeans you're at a greater risk of catching illnesses. According tomedical aviation expert Dr Mark Chanjo, some parts of the plane tendto get better ventilation than others. Where is ventilation usually a bitbetter?
　　Dr Mark ChanjoThe air is circulated about 12 to 15 times an hour. There is some variation, I mean, ifyou're sitting up in first class, you're going to have better ventilation than if you'resitting in the back of the aircraft.
　　Jackie:  Well, no surprises there. If you want better air, you'll have to pay moremoney and go in first class.
　　BBC Learning EnglishJackie:  Another flying-related problem which some people worry about iscalled deep vein thrombosis. This happens when the blood forms a clotin the leg. A clot is when the blood in a part of your body stops beingas liquid as it should be and sort of clumps together. But as MichaelBagshaw tells us, it is a rare problem – studies show it doesn't happenoften. How often does it happen, according to Michael?
　　MichaelIt would appear that the risk of thrombosis is about 1 per cent in people undergoingthese really long flights of greater than ten hours or so.
　　Jackie:  So only one in a hundred people is at risk of getting thrombosis on along flight. Michael says there's also a study which shows that thosewho did get the condition all had something in common about wherethey were sitting. What was it?
　　MichaelAll the deep vein thromboses that were detected occurred in people who were sittingin non-aisle seats, where, effectively, they were trapped and couldn't easily get out towalk around the cabin.
　　Jackie:  Michael said all those who got deep vein thrombosis were sitting innon-aisle sites. An 'aisle seat' is next to the part of the plane wherepeople walk up and down – 'the aisle' - so you're usually more able tomove your legs around if you sit there. Non-aisle seats are in betweenother seats or by the window and it's not so easy to stretch your legs.
　　Why is this important when it comes to deep vein thrombosis? Listento find out.
　　MichaelNormally of course the blood is fluid in the body and as we're walking around, theblood that is in the legs is actually being massaged by the muscles in the legs backinto the body. If you're sitting in an aircraft, or indeed any other seat for a long periodof time and not able to move about, that natural movement of the blood back towardsthe body simply doesn't take place, the blood stagnates in the leg, if you like, and insome cases you'll see the formation of a clot.
　　Jackie:  Michael says that if you're sitting and not able to move around much,the blood doesn't flow around your body properly. It stagnates – itstays where it is – and could form a clot.
　　A common problem with long flights occurs when you cross timezones. You might leave Japan in daylight, travel for 12 hours and whenyou arrive in England you're body is telling you it's bed time and itshould be night – but the problem is daytime has only just started inEngland. This is when you're at risk of something we call jet lag.
　　Natural light plays an important part in affecting the natural rhythm orcycle of our bodies, in particular, sleep. If we get a lot more daylightthan usual, it confuses our bodies. Listen to Michael. How long does itusually take us to get used to the change?
　　MichaelNow the body's rhythm will still follow its own cycle, but what's now missing is thetrigger which resets it is coming at the wrong time. So the sun is rising not when itshould it train with the body, so the body has to be reset – its time clock has to bereset - and it takes a few days for this to happen.
　　Jackie:  Did you get the answer? It usually takes a few days for us to get overet lag because our body clock has to reset – start again and get used tothe new daylight hours. No wonder flying makes us so tired. Ourbodies have to work hard to cope with so many changes. I think nexttime I go on holiday, I'll just take a short train ride down to the seaside– much less stressful!
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