Multiple: Motion Sickness

Definition
Description
Demographics
Causes and Symptoms
Diagnosis
Treatment
Prognosis
Prevention
The Future
For more information

Definition

Motion sickness is a feeling of nausea or dizziness produced by conflicting information provided to the central nervous system by the various organs of sense perception. It is not a disorder or disease in the strict sense but a normal response to an abnormal situation, namely a disagreement between what the eyes see and what the organs of balance in the inner ear feel.

Description

Motion sickness is an ancient health issue for travelers, affecting seafarers for millennia and modern travelers by automobile, airplane, or spacecraft. It can also affect people on amusement park rides or playing computer simulation games. Motion sickness can even affect people riding on an animal; for example, the famous British desert soldier, Lawrence of Arabia, often became sick when riding on camels because the swaying of the animals from side to side as they walked across the sand made him feel dizzy and nauseated.

People vary in the intensity of the symptoms they experience during motion sickness. For most people it is only a minor problem, but some people become so sick that they are almost incapacitated. One difference between the nausea and vomiting caused by motion sickness and that caused by many digestive disorders is that vomiting does not usually relieve the sick feeling in motion sickness; the person may continue to vomit without feeling better.

Demographics

The demographics of people experiencing motion sickness vary somewhat depending on the mode of travel; almost 100 percent of people

will get seasick on a boat in very rough waters but only about 30 percent will feel seasick sailing in relatively calm water. According to the Centers for Disease Control and Prevention (CDC), small boats and automobiles are the methods of travel most likely to produce motion sickness.

Some groups of people are more likely to develop motion sickness than others:

• Children. About 50 percent of children between the ages of two and twelve get carsick.
• People with migraine headaches.
• Women, particularly women who are pregnant or menstruating.
• Airline pilots. About 29 percent get airsick during flights; 70 percent experience motion sickness when training in flight simulators.
• Athletes. It is thought that athletes may be more susceptible to motion sickness because they have finely tuned senses and may be more aware of conflicting sensory input than most people.
• Astronauts. About 60 percent of United States astronauts experience space sickness during their first shuttle flight. Motion sickness is thought to be more common in larger spacecraft because the astronauts can move around more freely.

Causes and Symptoms

The basic cause of motion sickness is a disagreement between the eyes' perception of movement and the inner ear's perception of balance and the body's orientation in space. The human sense of balance depends on the complex interaction of five different parts of the body:

• The inner ear's vestibular system. The vestibular system is a group of organs in the inner ear that provide sensory input related to movement, orientation in space, and balance. This system detects

• and monitors the motions of the head, such as rotation of the head on the neck, and up-and-down, forward-and-backward, and side-to-side motions of the head.
• The eyes. The eyes help people locate themselves in space (whether they are upside down or right side up, for example) and identify the direction in which they are moving.
• Pressure receptors. These sensory receptors are located in the joints and spine; they tell the central nervous system what parts of the body are touching the ground.
• Sensory receptors in the muscles and joints. These receptors can tell what parts of the body are in motion.
• The central nervous system. The brain has to process inputs from the eyes, ears, pressure receptors, and muscle receptors, combine all this information, and interpret it.

If the combined sensory information is contradictory, the brain becomes confused. For example, someone riding in an airplane that has hit a patch of air turbulence may sense the up-and-down motion of the airplane through the pressure receptors in the body but not see any evidence of movement through the eyes. The brain receives messages that don't match or add up. One theory as to why this mismatch causes nausea and vomiting is that the part of the brain that resolves disagreements between what the eyes see and what the rest of the body feels is the same part that causes vomiting when a person eats something harmful or toxic. This area is called the area postrema and is located in the lower part of the brain stem. This theory holds that when the eyes and the inner ear send the brain conflicting messages, the area postrema decides that one of the senses is mistaken, that the mistake is due to a toxin, and that vomiting is necessary to get rid of it.

The symptoms of motion sickness include abdominal cramping, nausea, vomiting, dizziness, a pale complexion, and cold sweats. Motion sickness caused by training in a flight simulator includes eyestrain, headache, difficulties focusing or concentrating, and being unsteady on one's feet for several hours afterward. The Federal Aviation Administration (FAA) now recommends that pilots avoid flying or even driving for several hours after a simulator session.

Diagnosis

Diagnosis of motion sickness is usually based on the circumstances in which the person feels nauseated. Most people can tell when they are affected by motion sickness without consulting a doctor.

Treatment

Treatment for motion sickness usually includes preventive measures, discussed in the next section, and medications. The choice of medication depends on the length of the trip, any underlying medical conditions that the traveler may have, and concerns about drowsiness as a side effect. For example, airline pilots who have problems with airsickness are not allowed to take any medications that cause sleepiness or visual disturbances while they are in command of the plane.

Some medications for motion sickness, like Benadryl, Bonine, and Dramamine, can be taken by mouth and are available without a prescription. They should be taken between thirty minutes to an hour before the trip in order to allow them to be absorbed through the digestive tract. Scopolamine, a prescription medication, is available in both an oral form (to be taken by mouth) and a transdermal patch (the medicine is absorbed through the skin). The patch is applied behind the ear four hours before the trip and can be replaced every three days if needed. The medication in the patch that prevents nausea is absorbed through the skin. All drugs taken to prevent motion sickness, however, can cause drowsiness, dry mouth, blurred vision, and loss of coordination. People should use these medications with caution if they plan to drive, operate machinery, or go swimming or diving underwater. They should never combine these medications with alcohol.

Some types of alternative treatments that work for some people include drinking ginger tea or chewing on candied ginger. Ginger has long been used in traditional Chinese medicine to prevent nausea and is commonly recommended for morning sickness in pregnant women. Ginger also has the advantage of not causing drowsiness as a side effect. Another alternative treatment that benefits some travelers is the use of wrist bands or electric devices that stimulate a point on the wrist called the P6 point in acupuncture. The point is located about an inch and a half below the crease where the wrist meets the hand.

Most people recover from motion sickness without any difficulty. However, people who do not get better or whose symptoms get worse

should see a doctor quickly—they may need specialized treatment by a neurologist (doctor who specializes in treating disorders of the nervous system) or an otorhinolaryngologist (doctor who specializes in disorders of the ears, nose, and throat). Seeing a doctor is particularly important if the patient has trouble walking, cannot see clearly, or is losing their sense of hearing.

Prognosis

Most people who experience motion sickness feel better fairly quickly after their trip is over, although some people who suffer from severe sea-sickness may feel sick for two or three days after reaching land. Many people who travel frequently often develop a tolerance for the particular types of motion associated with a specific method of transportation; sailors sometimes speak of “getting one's sea legs” as a way of describing getting used to the motions of a ship without getting seasick.

Prevention

In addition to taking medications to prevent or minimize motion sickness, the CDC recommends the following preventive measures:

• Choose a seat that will provide a smoother ride—a seat where the eyes will see the same motion that the body and inner ears feel. These are the front seats of cars, the forward cars of trains, the center of a boat, and the seats over the wings of an airplane.
• Focus on the scenery outside the vehicle or the distant horizon rather than trying to read or looking at objects inside the vehicle.
• Minimize motions of the head and close the eyes. If possible, lie flat on the back or take a nap.
• Eat a light meal without fatty or spicy foods before traveling; do not eat a heavy meal before a trip or travel on a completely empty stomach.
• Do not drink alcoholic beverages or smoke.
• Try to minimize emotional stress and anxiety.
• If possible, open a nearby window or vent and breathe in some fresh air.

The Future

Given the popularity as well as the necessity of travel for many people, motion sickness is likely to continue to be a common problem for

travelers. Fortunately, it is almost always a minor inconvenience rather than a life-threatening condition.

SEE ALSO Headache

WORDS TO KNOW

Area postrema : The part of the brain stem that controls vomiting.

Brain stem : The lower part of the brain that joins the spinal cord. It controls breathing, pain perception, and other vital functions.

Transdermal : Referring to a type of drug that enters the body by being absorbed through the skin.

Vestibular system: The group of organs in the inner ear that provide sensory input related to movement, orientation in space, and balance.

For more information

BOOKS

Fujimoto, Gary R., and Marc R. Robin. The Traveler's Medical Guide. St. Paul, MN: Prairie Smoke Press, 2003.

Shannon, Joyce Brennfleck, ed.Traveler's Health Sourcebook. Detroit, MI: Omnigraphics, 2000.

PERIODICALS

Brody, Jane E. “Personal Health: A Stable Life, Despite Persistent Dizziness.” New York Times, January 15, 2008. Available online at http://query.nytimes.com/gst/fullpage.html?res=9C05E2D9113FF936A25752 C0A96E9C8B63&sec=&spon=&pagewanted=all (accessed May 14, 2008).

Derowitsch, Rachel. “Motion Sickness.” PC Today 4 (May 2006): 88. Available online at http://www.pctoday.com/editorial/article.asp?article=articles/2006/t0405/33t05/33t05.asp&guid= (accessed May 14, 2008).

WEB SITES

American Academy of Otolaryngology—Head and Neck Surgery. Dizziness and Motion Sickness. Available online at http://www.entnet.org/HealthInforma tion/dizzinessMotionSickness.cfm (accessed May 14, 2008).

Centers for Disease Control and Prevention (CDC). Travelers' Health: Motion Sickness. Available online at http://wwwn.cdc.gov/travel/yellowBookCh6-MotionSickness.aspx (accessed May 14, 2008).

KidsHealth. What's Motion Sickness? Available online at http://kidshealth.org/kid/talk/qa/motion_sickness.html (accessed May 14, 2008).