Motion Sickness

Motion Sickness 

Definition

Motion sickness is the uncomfortable dizziness, nausea, and vomiting that people experience when their sense of balance and equilibrium is disturbed by constant motion. Riding in a car, aboard a ship or boat, or riding on a swing all cause stimulation of the vestibular system and visual stimulation that often leads to discomfort. While motion sickness can be bothersome, it is not a serious illness, and can be prevented.

Description

Motion sickness is a common problem, with nearly 80% of the general population suffering from it at one time in their lives. People with migraine headaches or Ménière's syndrome, however, are more likely than others to have recurrent episodes of motion sickness. Researchers at the Naval Medical Center in San Diego, California, reported in 2003 that 70% of research subjects with severe motion sickness had abnormalities of the vestibular system; these abnormalities are often found in patients diagnosed with migraines or Ménière's disease.

While motion sickness may occur at any age, it is more common in children over the age of two, with the majority outgrowing this susceptibility.

When looking at why motion sickness occurs, it is helpful to understand the role of the sensory organs. The sensory organs control a body's sense of balance by telling the brain what direction the body is pointing, the direction it is moving, and if it is standing still or turning. These messages are relayed by the inner ears (or labyrinth); the eyes; the skin pressure receptors, such as in those in the feet; the muscle and joint sensory receptors, which track what body parts are moving; and the central nervous system (the brain and spinal cord), which is responsible for processing all incoming sensory information.

Motion sickness and its symptoms surface when conflicting messages are sent to the central nervous system. An example of this is reading a book in the back seat of a moving car. The inner ears and skin receptors sense the motion, but the eyes register only the stationary pages of the book. This conflicting information may cause the usual motion sickness symptoms of dizziness, nausea and vomiting.

Causes and symptoms

While all five of the body's sensory organs contribute to motion sickness, excess stimulation to the vestibular system within the inner ear (the body's "balance center") has been shown to be one of the primary reasons for this condition. Balance problems, or vertigo, are caused by a conflict between what is seen and how the inner ear perceives it, leading to confusion in the brain. This confusion may result in higher heart rates, rapid breathing, nausea and sweating, along with dizziness and vomiting.

Pure optokinetic motion sickness is caused solely by visual stimuli, or what is seen. The optokinetic system is the reflex that allow the eyes to move when an object moves. Many people suffer when what they view is rotating or swaying, even if they are standing still.

Additional factors that may contribute to the occurrence of motion sickness include:

Often viewed as a minor annoyance, some travelers are temporarily immobilized by motion sickness, and a few continue to feel its effects for hours and even days after a trip (the "mal d'embarquement" syndrome).

Diagnosis

Most cases of motion sickness are mild and self-treatable disorders. If symptoms such as dizziness become chronic, a doctor may be able to help alleviate the discomfort by looking further into a patient's general health. Questions regarding medications, head injuries, recent infections, and other questions about the ear and neurological system will be asked. An examination of the ears, nose, and throat, as well as tests of nerve and balance function, may also be completed.

Severe cases of motion sickness symptoms, and those that become progressively worse, may require additional, specific tests. Diagnosis in these situations deserves the attention and care of a doctor with specialized skills in diseases of the ear, nose, throat, equilibrium, and neurological system.

Treatment

There are a variety of medications to help ease the symptoms of motion sickness, and most of these are available without a prescription. Known as over-the-counter (OTC) medications, it is recommended that these be taken 30-60 minutes before traveling to prevent motion sickness symptoms, as well as during an extended trip.

Drugs

The following OTC drugs consist of ingredients that have been considered safe and effective for the treatment of motion sickness by the Food and Drug Administration:

Each of the active ingredients listed above are antihistamines whose main side effect is drowsiness. Caution should be used when driving a vehicle or operating machinery, and alcohol should be avoided when taking any drug for motion sickness. Large doses of OTC drugs for motion sickness may also cause dry mouth and occasional blurred vision.

The side effects of cinnarizine and the other antihistamine antiemetics indicate that they should not be used by members of flight crews responsible for the control of aircraft or for other tasks that require sustained attention and alertness.

The Food and Drug Administration (FDA) recommends that people with emphysema, chronic bronchitis, glaucoma, or difficulty urinating due to an enlarged prostate do not use OTC drugs for motion sickness unless directed by their doctor.

Longer trips may require a prescription medication called scopolamine (Transderm Scop). Formerly used in the transdermal skin patch (now discontinued), travelers must now ask their doctor to prescribe it in the form of a gel. In gel form, scopolamine is most effective when smeared on the arm or neck and covered with a bandage.

Another prescription drug that is sometimes given for motion sickness is ondansetron (Zofran), which was originally developed to treat nausea associated with cancer chemotherapy. Unlike cyclizine, ondansetron appears to be safe for use in children under the age of six.

Several newer antiemetic medications are under development as of early 2004. The most promising of these newer drugs is a class of compounds known as neurokinin-1 (substance P) antagonists. The neurokinins are being tested for the control of nausea following cancer chemotherapy as well as nausea related to motion sickness. In March 2003 the FDA approved the first of this new class of antiemetic drugs. Known as aprepitant, it is sold under the trade name Emend.

Alternative treatment

Alternative treatments for motion sickness have become widely accepted as a standard means of care. Ginger (Zingiber officinale) in its various forms is often used to calm the stomach, and it is now known that the oils it contains (gingerols and shogaols) appear to relax the intestinal tract in addition to mildly depressing the central nervous system. Some of the most effective forms of ginger include the powdered, encapsulated form; ginger tea prepared from sliced ginger root; or candied pieces. All forms of ginger should be taken on an empty stomach.

Placing manual pressure on the Neiguan or Pericardium-6 acupuncture point (located about three finger-widths above the wrist on the inner arm), either by acupuncture, acupressure, or a mild, electrical pulse, has shown to be effective against the symptoms of motion sickness. Elastic wristbands sold at most drugstores are also used as a source of relief due to the pressure it places in this area. Pressing the small intestine 17 (just below the earlobes in the indentations behind the jawbone) may also help in the functioning of the ear's balancing mechanism.

There are several homeopathic remedies that work specifically for motion sickness. They include Cocculus, Petroleum, and Tabacum.

Prognosis

While there is no cure for motion sickness, its symptoms can be controlled or even prevented. Most people respond successfully to the variety of treatments, or avoid the unpleasant symptoms through prevention methods.

Prevention

Because motion sickness is easier to prevent than treat once it has begun, the best treatment is prevention. The following steps may help deter the unpleasant symptoms of motion sickness before they occur:

Resources

Books

Pelletier, Dr. Kenneth R. The Best Alternative Medicine. New York: Simon and Schuster, 2002.

Periodicals

Black, F. O. "Maternal Susceptibility to Nausea and Vomiting of Pregnancy: Is the Vestibular System Involved?" American Journal of Obstetrics and Gynecology 185, Supplement 5 (May 2002): S204-S209.

Bos, J. E., W. Bles, and B. de Graaf. "Eye Movements to Yaw, Pitch, and Roll About Vertical and Horizontal Axes: Adaptation and Motion Sickness." Aviation, Space, and Environmental Medicine 73 (May 2002): 434-444.

Hamid, Mohamed, MD, PhD, and Nicholas Lorenzo, MD. "Dizziness, Vertigo, and Imbalance." eMedicine September 17, 2002. http://emedicine.com/neuro/topic693.htm.

Harm, D. L., and T. T. Schlegel. "Predicting Motion Sickness During Parabolic Flight." Autonomic Neuroscience 31 (May 2002): 116-121.

Hoffer, M. E., K. Gottshall, R. D. Kopke, et al. "Vestibular Testing Abnormalities in Individuals with Motion Sickness." Otology and Neurotology 24 (July 2003): 633-636.

Keim, Samuel, MD, and Michael Kent, MD. "Vomiting and Nausea." eMedicine April 29, 2002. http://emedicine.com/aaem/topic476.htm.

Liu, L., L. Yuan, H. B. Wang, et al. "The Human Alpha(2A)-AR Gene and the Genotype of Site −1296 and the Susceptibility to Motion Sickness." [in Chinese] Sheng Wu Hua Xue Yu Sheng Wu Wu Li Xue Bao (Shanghai) 34 (May 2002): 291-297.

Loewen, P. S. "Anti-Emetics in Development." Expert Opinion on Investigational Drugs 11 (June 2002): 801-805.

Nicholson, A. N., et al. "Central Effects of Cinnarizine: Restricted Use in Aircrew" Aviation, Space, and Environmental Medicine 73 (June 2002): 570-574.

O'Brien, C. M., G. Titley, and P. Whitehurst. "A Comparison of Cyclizine, Ondansetron and Placebo as Prophylaxis Against Postoperative Nausea and Vomiting in Children." Anaesthesia 58 (July 2003): 707-711.

Patel, L., and C. Lindley. "Aprepitant—A Novel NK1-Receptor Antagonist." Expert Opinion in Pharmacotherapy 4 (December 2003): 2279-2296.

Organizations

Civil Aerospace Medical Institute. P. O. Box 20582, Oklahoma City, OK 73125. (202) 366-4000. 〈http://www.cami.jccbi.gov〉.

National Aeronautics and Space Administration. Office of Biological and Physical Research. http://www.spaceresearch.nasa.gov.

Vestibular Disorders Association. P.O. Box 4467, Portland, OR 97208-4467. (800) 837-8428. http://www.teleport.com/∼veda.

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motion sickness

n.

Nausea and dizziness induced by motion, as in travel by aircraft, car, or ship. Also called kinesia.

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motion sickness

discomfort observed by some companion animals while being transported. It is caused by irregular and abnormal motion that disturbs the organs of balance located in the inner ear. There may be hypersalivation, restlessness and vomiting.