When motion sickness goes along for the ride

FDA Consumer, March, 1985 by Bill Rados

While motion sickness can ruin one's pride, one's suit, or an entire vacation, it seldom causes severe health complications. In extreme cases, though, prolonged vomiting can bring about severe headache, prostration, dehydration and disturbed mineral balance in the body. Motion sickness is not a fatal disease, but that is not always taken as good news by those sufferers who'd pay any price for relief.

The reasons for the body's unpleasant reaction to movement other than by its own two feet are not fully known. Whatever the reason, the process by which motion sickness occurs in the body centers around the inner ear. (It is known that individuals whose inner ear apparatus is not functioning, such as deaf persons, are immune to motion sickness.) The inner ear is an organ not only of sound but also of balance. It contains three fluid-filled, hollow tubes called the semicircular canals. The canals work like a gyroscope. The shifting of the fluid as the body moves sends signals to the brain to let us know (even with our eyes closed) the direction our bodies are moving--forward or backward, up or down, or sideways. The inner ear also contains a number of calcium crystals called otoliths that are sensitive to the pull of gravity. Signals from the otoliths to the brain tell whether the head is erect, tilted or upside down.

In some instances, motion sickness can be brought on simply by overstimulation of the inner ear. But more commonly the sense of sight is involved in the process, too. According to one widely accepted theory, riding in a vehicle can cause a "mismatch" between the signals from the inner ear about the position of the body and the signals from the eyes. The "mismatch" affects the brain's chemoreceptor trigger zone, which sends a command to a part of the medulla oblongata ominously known as the vomiting center. It doesn't take a medical degree to guess what happens next.

Consider, for example, one of most common situations in which motion sickness occurs--someone reading while riding in the back seat of a car. The semicircular canals of the inner ear register the movement of the car. But the eyes are fixed on the book or newspaper that is not moving in relation to the reader. Sensory conflict occurs and the sickness-inducing signals work their way from the vomiting center to the stomach, mouth and other organs.

Prevention is easier than treating motion sickness once it has begun. While the best method of prevention is to limit one's travel to that which can be done by foot or by National Geographic, a number of precautions can provide some help:

* Place yourself where there is the least motion. In a car, sit in the front seat, looking ahead. In an airplane, choose a seat over the wing. On a ship, remain amidship (preferably on deck), rather than below.

* Lie on your back, in a semi-reclined position, and keep your head as still as possible.

* Look ahead, at the distant horizon. If that's not possible, it may be better to close your eyes rather than focus on fast-moving scenery or waves. Children especially can be helped by having them sit in the front seat of a car, in an elevated safety seat if appropriate. This enables them to see through the frong windshield rather than looking at the inside of the car.