What is motion sickness? |

Causes and Symptoms

Motion sickness appears to be caused by overstimulation of the balance centers of the inner ears by repeated back-and-forth and up-and-down movements. Messages are carried from this area of the inner ear, known as the vestibular apparatus, to the medulla oblongata in the brain, which is responsible for the vomiting reaction. The nerve pathways for this journey are not entirely known, but certainly the cranial nerve, which is responsible for hearing and balance, is involved. Responses in the medulla oblongata set into motion automatic motor reactions in the upper gastrointestinal tract, diaphragm, and abdominal muscles that lead to vomiting.

Individuals vary considerably in their susceptibility to motion sickness, and experts believe that there may be an inherited tendency toward the problem. Shifting visual input (such as watching waves on the horizon), a poorly ventilated environment, and fear and anxiety all seem to play a role in the development and severity of motion sickness.

The diagnosis of motion sickness is usually self-evident. Vertigo, nausea, and vomiting follow exposure to a repetitive and usually irregular rocking motion while in a moving vehicle or on an amusement park ride. The first indication of motion sickness may be yawning, excessive salivation, pale skin, and sweating. The person may begin to breathe deeply or complain of sleepiness. The patient may also develop a need for air, dizziness, or a headache. In most cases, nausea and vomiting occur sooner or later. On an extended trip, patients with motion sickness may eventually develop a tolerance to the motion and feel better, or they may continue to feel sick. If severe rocking motions develop once again, however, patients may also become sick again. Repeated vomiting may lead to dehydration and low blood pressure. Depression is another feature of prolonged motion sickness.

Treatment and Therapy

This malady is far easier to prevent than to treat. People who suffer from motion sickness should avoid drinking liquids just before and during short trips. On longer trips, they should limit liquids and have only small, easy-to-digest foods at regular intervals. Plenty of fresh air may also help prevent sickness. Those prone to motion sickness should not read in a car or other moving vehicle. Focusing the eyes well above the horizon while riding in a car or on a boat may help. People who are susceptible to motion sickness should also avoid amusement park rides that involve swinging and rocking.

Sufferers of motion sickness may be treated with over-the-counter or prescription medications an hour before travel begins. Medications used for this purpose include diphenhydramine, promethazine, prcochlorperazine, chlorpromazine, scopolamine, dimenhydrinate, cyclizine, buclizine, and meclizine. They are available in a variety of forms, including tablets, rectal suppositories, and transdermal patches. Many of these drugs cause sleepiness, which may be helpful during a trip but cause drowsiness or lack of alertness on arrival. Another common side effect of some of these drugs is dry mouth. In most cases, these medications are more effective when given before vomiting begins. An extract of ginger root has been recommended as a treatment using a natural substance, and so having fewer side effects. Some objective studies, however, have failed to demonstrate its efficacy.

If the person has already begun vomiting, medications must be given by injection, rectal suppository, or a transdermal patch. In cases of prolonged vomiting, where dehydration is a concern, the patient may require intravenous fluids. Of particular concern is the individual who is already ill with another disease and also suffers from motion sickness. Such patients may have serious complications related to the vomiting and resulting dehydration.

Nonpharmacologic treatments for motion sickness abound. The best known are acupressure wristbands. The autogenic-feedback training (AFT) exercise, designed by the National Aeronautics and Space Administration (NASA), is a self-regulation and biofeedback training scheme that has shown promise in studies of space motion sickness in astronauts. It requires a minimum of six hours of training and so is not the quick fix that drugs promise. NASA scientists have also explored devices for holding the astronaut’s head steady, since head movement appears to exacerbate motion sickness. Such an apparatus might be applicable to the civilian population as well.

Perspective and Prospects

Motion sickness is a common problem in children and some adults. New drugs to treat the problem are being explored. A number of chemicals showing promise are related to or interact with serotonin, a chemical that participates in a number of regulatory systems in the body. Drug companies are working on new drug delivery systems to make antinausea medications easier to take. Other advances include drug regimens that will provide antinausea effects without sleepiness.

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