Motion Sickness

A typical Alberta summer day - bumpy. As you buck through the turbulence, that old familiar feeling returns - dry mouth, sweaty palms, rising breakfast. Your flight instructor smiles at you from the right seat, and asks if you’d care to demonstrate an accelerated stall. Something about your sweaty, pale complexion tells her what every instructor learns early. NOT today! Motion sickness is something we have all experienced to one degree or another, but don’t really understand. As with many other aviation medicine topics, myths abound. So, what is it, why does it happen and what can one do about it?

Motion sickness follows a well recognized, orderly sequence of symptoms. Vague stomach discomfort, often accompanied by yawning and mild headache, progresses to nausea and facial pallor. Cold sweating follows, with excess salivation and the loss of interest in complex tasks such as flying. Finally vomiting intervenes, and this cycle may wax and wane over time. The illness usually persists for several hours after landing.

The theory behind motion sickness is a hot topic in aerospace medicine these days, as Space Sickness, affecting 50% of all astronauts, is thought to be a similar process. The currently accepted theory is called “internal mismatch”. Your brain integrates the inputs from your vestibular (balance) organs with the most powerful orientation input, your vision. If the two match as expected (i.e. balance organs signal right tilt and eyes see a tilted horizon), then the brain is happy. If the two don’t match (i.e. coordinated turn in an aircraft where horizon tilts but balance organs sense no tilt) then the brain suspects poisoning, and does its best to empty the stomach. This theory is suggested by several observations. Humans born without inner ear balance organs due to birth defects cannot be made motion sick. Infants, who don’t integrate well, also don’t get motion sick. Motion sickness starts at the age when walking (and integration) begins and peaks at about age 12. “Motion” sickness can even because without any motion, in an IMAX movie theater for instance, another example of visual input not matching balance messages. For the same reason flight simulators can be very nauseating – as they are faking the movements of flight and your inner ear knows it!

So why don’t we all get sick in a coordinated turn? First of all, everyone has a different threshold of susceptibility. Usually, nasty stimuli have to be sustained to cause illness. Secondly, motion sickness can be unlearned (adaptation). Fascinatingly, high time jet pilots get motion sick in simulator cockpits more than non-pilots. Frigate naval captains can get sea sick when they transition to aircraft carriers. The reason is simple. Their brains have learned to expect certain inputs, and when our jet jock racks the simulator into what should be a three G turn, and feels a one G slip instead - here comes breakfast!

What do you do about it? Firstly, try to limit head movement all you can. The less chaos being fed into the system by swirling balance organs, as you retrieve charts from underneath your seat, the better. One of the problems we have in the airline industry is flight attendants in the galley looking down to count pop cans, or opening galley trays. Their head movement in the horizontal axis of the aircraft can be quite provoking for motion sickness. The best thing for a flight attendant to do is to align himself or herself along the longitudinal axis of the aircraft and avoid moving their head excessively. For passengers, lying reclined decreased motion sickness by 20% in one recent study. Secondly, look at the horizon, not inside the aircraft. Try to stabilize both your visual and balance inputs, so they match up again. Lots of cold fresh air helps, as does mentally occupying your mind with flight tasks. Anxiety or fear cause the same physical changes that motion sickness does, and contribute to it. Seeking stable air at different altitudes goes without saying.

A word of encouragement to students. A Royal Air Force study in 1974 revealed 39% of all trainees got motion sickness and a massive USAF survey in 1984 showed 55 to 83% of all trainees experience motion sickness on more than one training flight. The more you fly, the less troublesome motion sickness becomes, as your brain learns to ignore the bumps, “accommodating” to the new environment. Fly early in the morning, for smoother air, and take your aerobatics a bit at a time. Fly frequently. Give your brain time to adapt. Remember, that the new model is fragile, and will tend to decay at a different rate for different people. Speaking for myself, my model lasts approximately 30 or 45 days. If I have not flown in this time, I will likely become slightly motion sick as I get back into the air again. One hour of flight time later, I have “refreshed” my model, and my problem is fixed for the time being. A word of caution. Stubbornly persisting through severe nausea or vomiting is rarely successful. All it does is provide a paired association between flying and the sights and smells associated with it, and nausea. You will find yourself getting sicker earlier and earlier on in the flight. It is best to discontinue the flight, and begin again under less provoking circumstances.

There are no approved drugs for pilots to combat motion sickness. The commonly used ones - dimenhydrinate (Gravol) and scopolamine (Transderm V patches) are both dangerously sedating. Passengers can use them though. Make sure Transderm patches are in place 12 hours before the flight. Another study evaluated Seabreeze acupressure bands and found them useless - no better than placebo. Anecdotal evidence suggests chewing ginger as an effective natural antidote to motion sickness. Certainly it is legal to try this, and it works for some people.

So, you’ve tried all that, and the old familiar feeling is creeping up on you. Because of its common nature, motion sickness is often discounted as a cause for accidents, but it is a potent disabler, if allowed to progress far enough. In end stage motion sickness, the vestibular system is driving the eyes into a high-speed vibration termed “nystagmus “, making vision impossible and apathy progresses to total prostration. Once motion sickness is well established beyond the simple nausea stage, treat it like any other in-flight medical emergency and land as soon as safely possible. Lastly, if it is seriously interfering with your training, an aviation physician can consult with both you and your flight instructor to design a regime to allow your vestibular system to accommodate to the aviation environment. Every major Air Force in the world has such a program, and they have been employed with significant successes, so do not let motion sickness defeat you!

Brendan Adams MD FCBOM