Farrol Kahn is the founder and director of the Aviation Medicine Institute, an independent U.K.-based charity concerned with aviation health issues. He is the author of several books on aviation medicine, including Why Flying Endangers Your Health. Kahn recently spoke with Vision managing editor John Meakin.
JM With regard to powered flight, how would you assess the significance of the incredible things that have been achieved?
FK Flight is a profound event for us all because it has changed the world from a huge place to a sort of global village. At the drop of a hat we can fly anywhere in the world, and I think that’s quite a great achievement in the past hundred years. But like all new things, there is a positive and a negative aspect to it.
JM You say it has a hidden side. What would you say is the number one issue affecting the safety of flying?
FK I think the most significant one is the lack of oxygen. More people die in flight, mainly through heart attacks, than are killed in air crashes every year. And the main reason is the oxygen lack: we make do with maybe 25 percent less oxygen up there. Aircraft cabins are pressurized to a level between altitudes of 6,000 and 8,000 feet. That means that our main organs, the heart and the lungs, are stressed. For the average fit person that’s fine; we recover as soon as we are back on the ground. But up there our heart is beating faster, our lungs are breathing faster to compensate for it, and our blood is becoming thicker.
The next significant issue is deep-vein thrombosis (DVT)—a blood clot in the deep veins of the leg. The first contributory factor, which is common to all forms of transport, is prolonged sitting. The second factor is the oxygen lack: as soon as you ascend to altitude, clotting factors increase by six to eight times. The third is barometric pressure, which causes swelling in the lower legs. A fourth contributing factor could be the fact that you are squeezed into your seat because of the narrow seat pitch. If you are in business class, your leg rest could be pressing against the back of your calf and blocking the venous return; or if you have long legs, your leg could be dangling off the end of the leg rest, again blocking the flow of blood.
Another significant health issue related to flying is cosmic radiation, which most people don’t know about. Over years of flying you accumulate doses of radiation, and this may lead to the formation of cancers. Traveling at 37,000 feet for four hours is equivalent to one chest X ray. On the ground, regulations limit chest X rays, and in fact sometimes they actually give them to you from the back rather than the front because of the vulnerability of certain organs. However, if you go from the U.K. to the United States and back, you could end up with four chest X rays without knowing it!
JM Are there people who shouldn’t fly?
FK As an institute, we want to encourage people to fly. But on our website we do list contraindications to flying. For example, if people have suffered from a severe lung disease like emphysema, or have had unstable angina, we would recommend having their doctor fill in a medical information form about their condition. Send it to the airline medical department, and they will say “Yes, you can fly” or “No, you can’t.” Or they may recommend supplementary oxygen.
JM What can or should individuals do to safeguard their health when flying?
FK They can take some preventative measures, such as wearing flight socks to compress the leg and prevent DVT. They can also take aspirin for DVT prevention. And then, of course, vitamins C and E after a flight to cut down the free radicals that are caused by radiation. It’s also good for people to know that if they are unfit, they can order supplementary oxygen. Most people don’t know that.
JM What about exercise?
FK The best exercise is before you fly, at the gate. Exercise done while flying hasn’t been shown to be effective, so it gives a false sense of security. You can do exercises and still get a DVT.
JM Summing it all up, what would be your message to passengers?
FK Whenever you fly, be alert. Always be prepared when you’re thinking of going on a journey by air. Think of what you’re up against: you’re in a pressurized cabin—an unnatural, hostile environment. Get to know the risks and take precautions against them.