This is what a 16-hour flight does to your body

Qantas announced recently that it plans to charter a non-stop Perth-London journey in 2018, the world’s longest non-stop flight. The 8,998 flight would take 17 hours — enough time to watch the whole of 24 again.

But what happens to your body on a long haul flight? Some high-altitude physiology might surprise you

Most flyers are familiar with the sensation of ears ‘popping’ as a flight takes off or lands — the feeling of vessels in the middle of your ears expanding. Ears ‘pop’ when the higher pressure is released by swallowing or other changes to the pressure in your ears, nose and throat.

By the same mechanism, bubbles of gas in fillings can also expand as the plane rises, leading to uncomfortable teeth for the duration of the flight.

Cabin pressure won’t affect breathing for anyone but the most serious COPD sufferers, and most effects of changing air pressure tend to be more pedestrian - for example, ears popping and sore teeth.

Also, you might find that you get a ‘full’ feeling in the gut, as other obvious pockets of gas make themselves known. Gas in bodily cavities expands at high altitudes, so lay off the beans and Jerusalem artichokes before flying.

One of the more serious effects of a long haul flight is, of course, jet lag. But beyond the obvious symptom of being sleepy in the day, or awake at night, jetlag affects your whole physiology including cortisol levels, which affect your physical functioning.

“Cortisol's low and high at certain times of the day and if you need them to be high when they're low then your physical and mental responses would not be adequate,” advises Dr Mike Townend, former chairman of the British Global And Travel Health Association and a senior lecturer at the University of Glasgow.

It can take travellers up to 48 hours for their diurnal rhythms to recover from long haul flights and Dr Townend advises postponing important functions such as business meetings — particularly for passengers travelling east into shortening days.

He notes the increasing use of melatonin tablets during and after flights, but notes that the drug is not licensed - not available from UK GPs - and advises against buying melatonin online where product could be counterfeit (meaning you can’t sure sure of tablets’ contents or dosage).

One may assume that deep vein thrombosis (DVT) and the dull business of compression stockings is best left to the bingo brigade. But anyone with a DVT risk — for example, with a family history of DVT — needs to keep up their circulation on a plane.

Evidence suggests that anyone on a journey four hours or longer should get up and walk around because foot and ankle exercises need pressure — namely, your own body weight — to work best.

People often spend a long haul flight watching films or listening to music, but given the ambient noise from fellow passengers and the nearby 140-decibel jet engine, you’re likely to jack volumes to dangerous levels.

Cabin humidity has been reported at lows of 10 per cent. Given that in the UK we usually enjoy humidity levels around 50 per cent — rarely falling below 35 per cent even in the summer — this can result in dry skin and uncomfortable contact lenses.

Dr Townend advises that it’s not as much of a problem as people expect it to be: “Dry air in the aircraft cabin makes the mucus membrane in the mouth and throat dry out a bit and makes you feel more thirsty, even if you're not.”

But dry air, combined with higher-than-usual consumption of alcohol, tea and coffee, means you can arrive to your destination dehydrated. The best way to prevent this is simply to avoid diuretics and stick to water and soft drinks.

And the one thing you really shouldn’t worry about...

Part of the air is recirculated and part of it is drawn in afresh from outside from the engine's air intakes so it's not completely recirculated all the time. Any communicable diseases are likely to be passed between seats, and passengers are not more likely to catch coughs or colds on a 17-hour flight than they would be on a non-stop 17-hour bus or coach journey

So relax and enjoy that 24 binge — Jack Bauer’s way more thrilling than the plane’s air circulation system.