At any given point there are hundreds of thousands of people in the skies travelling by air. For many, these journeys will pass by without consequence. But for some, a routine flight may trigger a health emergency.

Although these events are rare, with the demand and availability of air travel increasing, so too is the likelihood of an in-flight emergency occurring. A study last year showed that one in every 212 flights experiences some kind of in-flight emergency, while in 2013 it only occurred on an estimated one in every 604 flights. In-flight emergencies cover everything from bumps, cuts and minor injuries through to heart attacks.

While air travel is one of the safest modes of transport, it places many unique challenges on the human body – which is why it can sometimes trigger sudden health problems.

One of the key reasons air travel is so hard on the body is due to the cabin pressure.

The aircraft cabin is pressurised at a level of up to 8,000 feet above sea-level. This pressure change has a significant impact on many body systems, especially those containing gases (such as the respiratory and gastrointestinal systems).

As the pressure in the cabin increases, the amount of available oxygen decreases because the molecules are further apart. At sea-level, the air contains approximately 21% oxygen. But when flying at altitude, the air only contains the equivalent of 15% oxygen. To compensate, the........

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