Motion Sickness Health Article

Definition

Motion sickness is a condition characterized by uncomfortable sensations of 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 lead 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, and the muscle and joint sensory receptors (which track what body parts are moving). The central nervous system (the brain and spinal cord), 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 & 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. There are people who suffer from constant motion sickness. Names for these conditions vary, such as positional dizziness.

Pure optokinetic motion sickness is caused solely by visual stimuli; that is, by what is seen. The optokinetic system is the reflex that allows the eyes to move when an object moves. Many people suffer when they view rotating or swaying images, even if they are standing still. Optokinetic motion sickness is of particular concern to the civilian aviation industry as well as to military aerospace programs. In the United States, both the Federal Aviation Agency (FAA) and the National Aeronautics and Space Administration (NASA) have research programs for the prevention and treatment of optokinetic motion sickness.

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

• Poor ventilation lowers a person's threshold for experiencing motion.
• Anxiety or fear also lowers the threshold.
• Food. Physicians recommend avoiding heavy meals of spicy or greasy foods before and during a trip.
• Alcohol. A drink is often thought to help calm the nerves, but in this case it could upset the stomach further. A hangover for the next morning's trip may also lead to motion sickness.
• Pregnancy. 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.
• Genetic factors. Research 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.

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). For those with constant motion sickness, it may not stop at all.