Motion sickness

Definition

Motion sickness is uncomfortable dizziness , nausea , and vomiting that people experience when their sense of balance and equilibrium is disturbed because their brain cannot make sense of conflicting information about their body's location in space and motion in their environment.

Description

Motion sickness is connected to 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 ear (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 to the central nervous system (the brain and spinal cord). The brain then is responsible for processing all incoming information and making sense out of it. Riding in a car, being on a ship, or taking an amusement park ride can cause conflicting stimulation of the different sense organs. The result is motion sickness.

For example, when 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. While motion sickness can be bothersome, it is not a serious illness, and it can be prevented.

Demographics

Although nearly 80 percent of the general population experiences motion sickness at one time in their lives, children between the ages of four and ten are most vulnerable. Children often out grow motion sickness. Toddlers under age two are rarely motion sick. Adults who frequently get migraine headaches 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 percent of research subjects with severe motion sickness had abnormalities of the vestibular system. Research also suggests that some people inherit a predisposition to motion sickness. This predisposition is more marked in some ethnic groups than in others. One study published in 2002 found that persons of Chinese or Japanese ancestry are significantly more vulnerable to motion sickness than persons of British ancestry.

Causes and symptoms

While all 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 (vertigo) are often 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.

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

• nancy (
• poor ventilation
• anxiety or fear (Both have been found to lower a person's threshold for experiencing motion sickness symptoms.)
• food (A heavy meal of spicy and greasy foods before traveling is thought to increase motion sickness symptoms.)
• alcohol consumption
• genetic factors
• preg
• Susceptibility in women to vomiting during pregnancy appears to be related to motion sickness, although the precise connections are not well understood as of 2004.)

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.

When to call the doctor

Most cases of motion sickness are mild and self-limiting. Parents should call the doctor before giving young children over-the-counter medications for motion sickness. Some remedies are recommended only for older children.

Diagnosis

Most cases of motion sickness are self-diagnosed. 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 performed.

Severe cases of motion sickness or 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

Medications to help ease the symptoms of motion sickness are available without a prescription (over-the-counter or OTC). Normally these are taken 30 to 60 minutes before traveling to prevent motion sickness symptoms, as well as during extended trips.

Over-the-counter drugs

The following OTC drugs contain ingredients that are considered by the United States Food and Drug Administration (FDA) to be safe and effective for the treatment of motion sickness:

• Marezine (and others) includes the active ingredient cyclizine and is not for use in children under six years of age.
• Benadryl (and others) includes the active ingredient diphenhydramine and is not for use in children under age two without a doctor's permission.
• Dramamine (and others) includes the active ingredient dimenhydrinate and is not for use in children under two years of age.
• Bonine (and others) includes the active ingredient meclizine and is not for use in children under age 12.

The 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. Children should not be given OTC motion sickness medication without first checking with a healthcare professional.

Prescription drugs

Longer trips may require a prescription medication called scopolamine available in the form of a skin patch or gel that is rubbed on the skin. Another prescription drug that is sometimes given for motion sickness is ondansetron (Zofran), which was originally developed to treat nausea associated with cancer chemotherapy . It appears to be safe for use in children under the age of six. In March 2003, the FDA approved a new anti-emetic (anti-nausea) drug. Known as aprepitant, it is sold under the brand name Emend.

Alternative treatment

Ginger (Zingiber officinale ) in its various forms is often used to calm the stomach, and 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 are the powdered, encapsulated form; ginger tea prepared from sliced ginger root; and 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 they place 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

Motion sickness is not a serious disorder and almost always resolves once the conflicting motion messages have stopped.

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:

• Avoid reading while traveling.
• Ride in a location that allows the eyes to see the same motion that the body and inner ears feel. Safe positions include the front seat of the car (for older children) while looking at distant scenery; the deck of a ship where the horizon can be seen; and sitting by the window of an airplane. The least motion on an airplane is in a seat over the wings.
• Maintain a fairly straight-ahead view.
• Eat a light meal before traveling, or if already nauseated, avoid food altogether.
• Avoid watching or talking to another traveler who is having motion sickness.
• Take motion sickness medicine at least 30 to 60 minutes before travel begins or as recommended by a physician.

Even those who frequently endure motion sickness can learn to travel by anticipating the conditions of their next trip. Research also suggests that increased exposure to the stimulation that causes motion sickness may help decrease symptoms on future trips.

Parental concerns

Parental concerns center primarily on making the child comfortable and anticipating the logistics of traveling with a child who is motion sick. Rarely do children vomit to the point of becoming dehydrated. Prevention and practical steps such as taking something for the child to vomit into and carrying a change of clothes can ease parents' worries about motion sickness.

KEY TERMS

Acupressure —Often described as acupuncture without needles, acupressure is a traditional Chinese medical technique based on theory of qi (life energy) flowing in energy meridians or channels in the body. Applying pressure with the thumb and fingers to acupressure points can relieve specific conditions and promote overall balance and health. Also known as dian xue.

Acupuncture —Based on the same traditional Chinese medical foundation as acupressure, acupuncture uses sterile needles inserted at specific points to treat certain conditions or relieve pain.

Anti-emetic —A preparation or medication that relieves nausea and vomiting. Cola syrup, ginger, and motion sickness medications are examples of antiemetics.

Vertigo —A feeling of dizziness together with a sensation of movement and a feeling of rotating in space.

Vestibular system —The brain and parts of the inner ear that work together to detect movement and position.

Resources

BOOKS

ABBE Research Division Staff. Air, Sea, and Car Motion Sickness: Index and Analysis of New Knowledge. Washington, DC: A B B E Publishers Association, 2004.

Motion Sickness: A Medical Dictionary, Bibliography, and An Annotated Research Guide to Internet References. San Diego, CA: Icon Group International, 2004.

Pelletier, 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 (May 2002)(Supplement 5): S204–9.

Hoffer, M. E., et al. "Vestibular Testing Abnormalities in Individuals with Motion Sickness." Otology and Neurotology 24 (July 2003): 633–6.

O'Brien, C. M., et al. "A Comparison of Cyclizine, Ondansetron, and Placebo as Prophylaxis against Postoperative Nausea and Vomiting in Children." Anaesthesia 58 (July 2003): 707–11.

ORGANIZATIONS

Vestibular Disorders Association. PO Box 4467, Portland, OR 97208–4467. Web site: <www.teleport.com/~veda>.

WEB SITES

Hamid, Mohamed, and Nicholas Lorenzo. "Dizziness, Vertigo, and Imbalance." eMedicine, October 28, 2004. Available online at <www.emedicine.com/neuro/topic693.htm> (accessed January 12, 2005).

Keim, Samuel, and Michael Kent. "Vomiting and Nausea." eMedicine, July 13, 2004. Available online at <www.emedicine.com/aaem/topic476.htm> (accessed January 12, 2005).

Tish Davidson, A.M.
Beth Kapes
Rebecca Frey, PhD

motion sickness At some point in their lives, most individuals experience motion sickness, in one form or another, while being transported in moving vehicles. There is a wide variability in susceptibility, with a greater prevalence in females than males, and in children between 3 and 12 years of age. It is characterized by initial feelings of dizziness, general discomfort, pallor, and cold sweating, followed by nausea, vomiting, and apathy. It has been given many specific names relating to the mode of transport involved (such as sea-, air-, space-, or even camel-sickness), but all forms are thought to arise from the same basic cause.

The first known report of sea-sickness was by Hippocrates, and the word ‘nausea’ actually derives from the Greek for ship (naus). The precise cause has been difficult to establish, although it has long been realized that it is associated with stimulation of the vestibular system of the inner ear. Thus, motion sickness is never experienced by individuals who have no vestibular function. Older texts often suggest that the cause is over-stimulation of the vestibular system, but current opinion favours an explanation in terms of what has been called the sensory conflict theory of motion sickness. This is based on the notion that the stimuli which cause motion sickness are those that generate sensations that do not conform with a repertoire of expected sensations that has been built up and stored in the brain on the basis of past experience of the sensory stimulation associated with motion.

Two major sources of sensory conflict are recognized: intra-vestibular and visual–vestibular. Intra-vestibular conflict arises from the fact that there are two types of sensory organ in the vestibular system, the semicircular canals, which respond to rotation, and the otolith organs, which respond to linear motion and to changes in orientation with respect to gravity. If a rotational movement of the head is made, such as pitching the head forward to look down at the ground, the otoliths and canals independently give signals about the magnitude of the movement during and after the motion. Because such head movements are made very frequently, an internal representation of the association between these two signals is built up, so that they are then accepted as compatible. However, if the same head movement is made in a different context, the signals may become incompatible. For example, if such a head movement is made during prolonged rotation on a fairground carousel the sensation of head rotation will be influenced by the rotation of the carousel, resulting in a conflict with signals arising from the otolith organs. Equally, head movements made in space, where gravitational acceleration is almost eliminated, will elicit sensations of turning from the canals, which are not matched by the normal otolithic signals.

Visual–vestibular conflict may arise from the fact that the vestibular stimulation experienced with head motion stimuli is normally associated with a compatible visual impression of movement. If the motion of the visual scene is modified, as it is for example when viewing the world through binoculars from a moving vehicle, the incompatibility between the vestibular sensation and the visual motion sensation may be sufficient to induce motion sickness. Viewing the horizon from the deck of a ship on a rough sea helps to reduce motion sickness because the vestibular sensation is compatible with a stable visual world, whereas viewing the wave motion of the sea itself is likely to generate conflict. Apparent motion of the visual world, as generated by large, projected moving images (e.g. cinerama), in the absence of the head movement that would normally occur when seeing such images, may also provide sufficient conflict to induce motion sickness.

Associated with the concept of the sensory conflict hypothesis is the notion that continued exposure to new combinations of visual and vestibular motion stimuli should lead to adaptation of the internal model and thereby to reduced susceptibility. This is supported by the observation that individuals may initially experience motion sickness on a sea voyage, but quickly adapt and gain their ‘sea-legs’ within a period of 3–6 days. For those susceptible individuals who are continually exposed to provocative motion stimuli it is possible to carry out a process of adaptation based on this principle. For more limited periods of exposure there are some anti-motion sickness drugs (scopolamine, dimenhydrinate) that are effective in preventing the onset of sickness, at least for the period of the journey.

Graham Barnes

Motion Sickness

The Ruined Fishing Trip

What Causes Motion Sickness?

What Are the Symptoms of Motion Sickness?

How Can Motion Sickness Be Prevented?

Resource

Motion sickness occurs when people feel dizzy or nauseated because the motion their body senses and the motion their eyes perceive are not synchronized. The conflicting messages sent to the brain make them feel ill.

KEYWORDS

for searching the Internet and other reference sources

Internal medicine

The Ruined Fishing Trip

Jon and his dad were very excited about their upcoming deep sea-fishing trip off the Florida coast. Dad’s friend Bob had a boat and knew the right spots to look for fish. The sun was bright, and the sea was choppy that day. Bob traveled out about four miles from shore. Suddenly, his motor quit, and the boat vigorously bobbed up and down on the waves.

First Jon felt queasy in his stomach, and then he broke out in a cold sweat. He became nauseated and vomited over the side of the boat. When they got back to shore, Jon’s queasiness went away fairly rapidly. He felt frustrated that the pleasure of the fishing trip had been ruined by his bout of motion sickness.

What Causes Motion Sickness?

Dizziness, vertigo*, and motion sickness are all related to the sense of balance and equilibrium in the inner ear. Researchers in space and aeronautical medicine call this sense spatial orientation, because it tells the brain where the body is in space.

*vertigo

(VER-ti-go) is the feeling that either the environment or one’s own body is revolving or spinning, even though they are not.

The following sensors work together to maintain a sense of spatial orientation:

• The chamber of the inner ear known as the vestibular labyrinth (ves-TIB-u-lar LAB-e-rinth) consists of fluid-filled, interconnected tubes called semicircular canals that monitor the direction of motion.

• The eyes send signals to the brain about where the body is in space.
• Skin pressure receptors tell the brain what part of the body is touching the ground.
• Muscle and joint receptors tell the brain what parts of the body are moving.
• The brain processes all the information from these sensors and puts everything together. When information from the sensors appears to conflict, the brain is confused, and in many people motion sickness occurs. When the boat Jon was in was tossed about on the waves, information from Jon’s eyes did not match the information about the boat’s movement coming from other parts of his body. This caused him to feel uncomfortable and to vomit. The sensitivity to mixed sensory messages about movement seems to be inherited; motion sickness tends to run in families.

The Patch

One of the most effective methods of preventing motion sickness is known as “the patch.” The patch is a small spot bandage that is usually worn behind the ear. The patch slowly releases scopolamine (sko-PALL-a-meen) through the skin. Scopolamine works by suppressing certain areas of the central nervous system, which decreases motion-induced nausea and vomiting. The patch provides lasting protection against motion sickness for about 3 days. The most common side effect of the patch is dryness of the mouth. Other less common side effects include drowsiness and dilation (widening) of the pupils of the eyes.

What Are the Symptoms of Motion Sickness?

Almost everyone can get motion sickness at one time or another. Some people, especially children, become queasy when riding in a car or an airplane. Other people get seasick from the rocking motion of a boat on rough water. Some people feel sick from riding a roller coaster or a spinning carnival ride, or even watching a jumpy, fast-moving scene in a movie. Poor ventilation, odors such as gas fumes or smoke, and drinking alcohol make a person more susceptible to motion sickness. People feeling motion sick may:

• become pale
• yawn
• act restless
• break out in a cold sweat
• feel queasy as if they will have to vomit
• vomit, sometimes repeatedly

How Can Motion Sickness Be Prevented?

Preventing motion sickness is easier than treating it once it has begun.

Travelers should sit wherever there is the least motion. In a car, sitting in the front seat and looking straight ahead may help. In an airplane, passengers feel the least motion in a seat over the wing. On a ship, remaining on the deck and looking at the far horizon rather than nearby objects may help. Eating only a light meal before traveling and avoiding alcohol also help a person avoid motion sickness.

Over-the-counter medications such as meclizine or dimenhydrinate (Dramamine) can be effective in preventing motion sickness. They work best if taken an hour or so before traveling. Although it is not a proven medical remedy, some people rely on ginger root, either sliced and chewed or brewed as tea, as a way to prevent motion sickness. In severe or prolonged cases of motion sickness, a doctor may prescribe a scopolamine patch.

Once the symptoms of motion sickness start, they are difficult to treat while the upsetting motion continues. For most people, the symptoms stop soon after the motion stops. If the symptoms persist, the person should consult a physician, because another disorder may be causing the symptoms.

See also

Vertigo

Resource

American Academy of Otolaryngology—Head and Neck Surgery, One Prince Street, Alexandria, VA 22314-3357. This organization’s website provides information about the inner ear and how it controls balance.
Telephone 703-836-4444
http://www.entnet.org

motion sickness waves of nausea and vomiting experienced by some people, resulting from the sudden changes in movement of a vehicle. The ailment is also known as seasickness, car sickness, train sickness, airsickness, and swing sickness. The principal cause of the disturbance is the effect of motion on the semicircular canals of the inner ear, although other factors such as inadequate ventilation and fumes or noxious odors may contribute. Drugs are available that, when taken beforehand, prevent the occurrence of motion sickness.

motion sickness (travel sickness) (moh-shŏn) n. nausea, vomiting, and headache caused by motion during travel by sea, road, or air. The symptoms are due to overstimulation of the balance organs in the inner ear. Sedative antihistamine drugs are used for prevention and treatment.