Motion Sickness Definition
Motion sickness refers to certain temporary unpleasant feelings like dizziness and nausea associated with motion or a perception of motion when the body is stationary. It usually occurs when traveling by sea, air or land in which a person is sitting for long periods. The the brain perceives the motion with some senses yet other senses perceives the body as being stationary. These contradictory perceptions leads to motion sickness. The types of movements that usually cause motion sickness include repetitive movements, accelerations (increase in speed) and decelerations (decrease in speed). The symptoms of motion sickness are temporary and usually subside on their own when the motion stops.
Motion Sickness Incidence
Motion sickness affects people all over the world. It has no regional or ethnic bias although some small studies have shown that he Chinese are more susceptible. Women (especially pregnant women) are particularly vulnerable. Children aged between 3 to 12 years are the most susceptible. Elderly people show less susceptibility to motion sickness. It is therefore difficult to substantiate the incidence of motion sickness.
Motion Sickness Pathophysiology
Perception of Motion
The human brain perceives the state of motion or of rest based on the signals it receives from four different sensory systems in the body. These sensations are derived from the vestibular system in the inner ear, the eyes, the pressure receptors on the skin and the sensors in the muscles of the body. These four systems work together to give information to the brain about the body’s position ‘in space’.
Conflicting Signals of Movement
During intentional movements like walking, swimming, or running, all the sensory inputs mentioned above tell the brain the same thing – the body is in motion. The brain then acts on these inputs to successfully control of the body movements during motion. However, during an unintentional movement like sitting in a moving car, ship or plane, the different sensory inputs tell the brain different things.
For example, the eyes may tell the brain that they see movement, whereas the sensors in the muscles of the body may say that the body is sitting. Alternatively, the eyes may see the stationary interior of the vehicle and tell the brain that the body is not moving. However, the position sensors in the ears and muscles may tell the brain that they perceive movement in the form of repetitive jerks, accelerations and decelerations.
These types of conflicting signals confuse the brain in such a way that it cannot decide whether the body is in motion or at rest. Such a conflict in the perception of the body’s status generates the symptoms of motion sickness.
Sensory Input in Motion Sickness
The main sensory system responsible for motion sickness is the vestibular apparatus in the inner ear. Overstimulation of this system during any movement is primary responsible for generating the symptoms of motion sickness. If the sensory input from the vestibular apparatus to the brain is damaged, motion sickness does not occur. Also, the levels of neurotransmitters (chemicals used by nerve cells to communicate with each other) change during motion sickness. Therefore, many drugs used for treating motion sickness work by influencing the levels of neurotransmitters in the brain.
Motion Sickness Symptoms
Nausea is the main symptom of motion sickness. It might be accompanied by other symptoms like:
- Abdominal discomfort
- Irritability and headache
- Fatigue and drowsiness
- Yawning and belching
- Paleness of the skin (pallor)
- Sudden unwarranted sweating or profuse perspiration
- Increased salivation
These symptoms usually ease as the person adapts to the motion or if the motion stops. Sometimes vomiting may also help to relieve the intensity of the symptoms.
Motion Sickness Causes
Exposure to real or perceived motion stimuli causes motion sickness. The following types of motions often act as strong stimuli for motion sickness:
- Rolling at a certain angle
- Long periods of motion, even when barely perceptible, can still cause motion sickness. Examples include prolonged tilting of a train or a large ship.
- Virtual or visual perception of motion (like watching a movie or playing a video game) can also precipitate motion sickness.
- Emotional stress and negative emotions increase the tendency of motion sickness.
- A head injury or an infection of the inner ear on only one side can also result in a sense of vertigo, spinning, or nausea.
Following factors increase the risk of developing motion sickness:
- Previous episodes of motion sickness
- Pregnancy and the use of hormonal contraceptives
- Increased tendency of vomiting
- Inflammation of the inner ear
- Presence of migraine headaches
- Poor ventilation
- Fear and anxiety
- Migraine headaches
Motion Sickness Complications
Motion sickness rarely presents with other complications. It is usually a minor annoyance but may seriously affect traveling situations. Complications, if any, may arise from falls or from a combination of other recreational, travel, or occupational hazards.
Motion Sickness Treatment
The symptoms of motion sickness usually eases and resolves shortly thereafter when the motion that causes it ceases. However, in some people the symptoms may persist for longer and can even extend from hours to days after the stimuli ceases. Treatment is directed at preventing motion sickness or managing the symptoms. Treatment is more effective if applied before the exposure to the motion stimuli or appearance of significant symptoms. The choice of treatment depends on age, length of exposure, existing medical conditions, and ongoing medications.
Medication for Motion Sickness
- Drugs called anti-cholinergic agents reduce activity in the vestibular nuclei in the inner ear and decrease the perception of motion. These drugs have side effects like dryness of throat, sensitivity to bright light, dry mouth, and drowsiness.
- Over-the-counter anti-histamines (like cinnarizine, dimenhydrinate, meclizine, promethazine, and cyclizine) are used to prevent and treat motion sickness. These drugs are very effective in children.
- Drugs called sympathomimetics are rarely prescribed and given only to counter the sedative effects of other medications.
- Substances called amphetamines may be effective against motion sickness, but are prescribed with caution because of a high potential for abuse.
- A combination of caffeine with promethazine manages motion sickness in some patients. However, consumption of caffeine alone may increase motion sickness.
- Anti-emetic (anti-vomiting) drugs (like ondansetron) provide relief from nausea, but cannot prevent motion sickness.
- Benzodiazepines (like diazepam) have sedative properties and are prescribed only in severe and treatment-resistant cases.
- Oral, intranasal or transdermal (on skin) application of scopolamine is the most effective preventive and treatment measure in motion sickness.
Motion Sickness Prevention
Preventive measures are very helpful in managing motion sickness. This is however, not practical in this day and age of modern transportation.
- Dietary measures include taking high-carbohydrate, low-fat and bland diet. This may reduce the symptoms of motion sickness. Spices and acidic foods may cause gastrointestinal discomfort, nausea and vomiting.
- The situations that trigger motion sickness should be recognized and avoided as far as possible if not necessary.
- Vehicles, terrain and modes of transport should be chosen carefully. Traveling in large ships, comfortable cars, and smoothly accelerating trains cause less motion sickness. Conversely, traveling in small boats, buses and rocking trains can trigger motion sickness. Curved mountain roads are also a risk factor.
- Acclimatization to the motion stimuli also helps. Facing towards the direction of the motion, watching the sky, minimizing head motion and neck twisting, or lying down with closed eyes can reduce symptoms to a significant extent. Reading or watching a screen should be avoided during travel. Sitting towards the middle of the plane where air turbulence is less likely to be felt is advisable.
- Strong smells, extreme temperatures, and consumption of alcohol, nicotine and caffeine may increase nausea. These should be avoided during travel.