Jackie: Hello, this is Entertainment from BBC Learning English dot com with

me, Jackie Dalton. I've just got back from my Christmas holidays,

which involved taking a long flight. When I got off the plane, I felt

exhausted and now I've got a cold and I've often wondered why flying

often 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’ve

ever flown, you may have noticed that when the plane takes off, your

breathing becomes quicker and your pulse rate – the speed at which

your heart is beating – goes up. This may partly be because you’re

excited or nervous, there’s another reason. What is it? Listen to

Michael Bagshaw professor of aviation medicine at Kings College,

London, to find out.

Michael

As you take off from sea level, there’s quite a significant pressure change. The pulse

rate will go up very slightly so that you take in more oxygen and remove the excess

carbon dioxide from the system.

Jackie: When you take off there’s a pressure change so get as your body works

harder 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 a

plane is recycled - or reused – very often, which means you’re

breathing in a lot of other people’s air. The ventilation – the movement

of air – isn’t great and lots of people are together in a small space. This

means you’re at a greater risk of catching illnesses. According to

medical aviation expert Dr Mark Chanjo, some parts of the plane tend 

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to get better ventilation than others. Where is ventilation usually a bit

better?

Dr Mark Chanjo

The air is circulated about 12 to 15 times an hour. There is some variation, I mean, if

you’re sitting up in first class, you’re going to have better ventilation than if you’re

sitting in the back of the aircraft.

Jackie: Well, no surprises there. If you want better air, you’ll have to pay more

money and go in first class.

BBC Learning English

Jackie: Another flying-related problem which some people worry about is

called deep vein thrombosis. This happens when the blood forms a clot

in the leg. A clot is when the blood in a part of your body stops being

as liquid as it should be and sort of clumps together. But as Michael

Bagshaw tells us, it is a rare problem – studies show it doesn’t happen

often. How often does it happen, according to Michael?

Michael

It would appear that the risk of thrombosis is about 1 per cent in people undergoing

these 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 a

long flight. Michael says there’s also a study which shows that those

who did get the condition all had something in common about where

they were sitting. What was it? 

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Michael

All the deep vein thromboses that were detected occurred in people who were sitting

in non-aisle seats, where, effectively, they were trapped and couldn’t easily get out to

walk around the cabin.

Jackie: Michael said all those who got deep vein thrombosis were sitting in

non-aisle sites. An 'aisle seat' is next to the part of the plane where

people walk up and down – 'the aisle' - so you’re usually more able to

move your legs around if you sit there. Non-aisle seats are in between

other 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? Listen

to find out.

Michael

Normally of course the blood is fluid in the body and as we’re walking around, the

blood that is in the legs is actually being massaged by the muscles in the legs back

into the body. If you’re sitting in an aircraft, or indeed any other seat for a long period

of time and not able to move about, that natural movement of the blood back towards

the body simply doesn’t take place, the blood stagnates in the leg, if you like, and in

some 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 – it

stays where it is – and could form a clot.

A common problem with long flights occurs when you cross time

zones. You might leave Japan in daylight, travel for 12 hours and when

you arrive in England you’re body is telling you it’s bed time and it

should be night – but the problem is daytime has only just started in

England. This is when you’re at risk of something we call jet lag.

Natural light plays an important part in affecting the natural rhythm or

cycle of our bodies, in particular, sleep. If we get a lot more daylight 

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than usual, it confuses our bodies. Listen to Michael. How long does it

usually take us to get used to the change?

Michael

Now the body’s rhythm will still follow its own cycle, but what’s now missing is the

trigger which resets it is coming at the wrong time. So the sun is rising not when it

should it train with the body, so the body has to be reset – its time clock has to be

reset - 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 over

jet lag because our body clock has to reset – start again and get used to

the new daylight hours. No wonder flying makes us so tired. Our

bodies have to work hard to cope with so many changes. I think next

time I go on holiday, I'll just take a short train ride down to the seaside

– much less stressful!