What is motion sickness?
Motion sickness is a condition that occurs in humans when exposed to non-physiological and abnormal movement. It may occur either when the patient is in motion, the environment is in motion or a combination of the two. I use this term keeping in mind that humans were designed with certain limitations and restrictions regarding motion and their environment.
Our “blue print”of motion which has been set by genetic predispositionand developed from birth restricts us to our environment. We were designed to walk, run and operate on land. We do not have wings or fins and can therefore not fly or live in water. It is then specifically motion out of these normal human bounds that has the potential to cause motion sickness. In fact, motion intolerance may be normal and therefore motion sickness is not a real “sickness” as such. During motion our brains are bombarded with sensory information from the eyes, vestibular apparatus and musculosceletal system. Motion sickness occurs when there is an overload of sensory information causing conflict and confusion in our brains because it is unknown.
How common is motion sickness and who gets it?
Motion sickness is very common and with the appropriate motion stimulus nearly every person can develop it. The prevalence is more or less reported in the order of 28% but obviously this figure depends on the type of motion and the way that motion sickness is defined. Lawther and Griffen in 1988 reported that 7% of seagoing passengers experienced vomiting during a journey.
Females are more susceptable than males and it is also more common in females during their menstrual cycle.There is also a relationship between motion sickness and migraine. It is extremely rare before the age of 2 years where after it steadily increases to peak around 12 years. The incidence then stays steady excepts for 2 peaks in females near 35 and 50. These peaks are likely influenced by hormonal changes. There is a decline in the incidence in the elderly.
What causes motion sickness?
There may be a genetic susceptibility, but this is not yet established. The dominant theory is the sensory conflict theory. This theory is based on the fact that under normal circumstances the body is aware of its position in space by means of the brain interpreting the visualinformation from the eyes, the vestibular information from the inner ear and the proprioceptive and touch information from the musculoskeletal system. All of this information is then compared with the internal expectations of the brain, based on the bodies established bluebrint for motion. If there is conflict and disagreement motion sickness occur.
Other theories of motion sickness
There are also other theories. In 2004, Flanagan et al proposed a slightly different theory which states that during certain motion, emphasis is placed on the importance of one response whilst the others are denied. The reflexive eye movement theory is states that it is just high speed induced rapid eye movementsthat causes motion sickness. The postural instability theory suggests that body movement, rather than sensory conflict or eye movement is to blame. In astronauts, space sickness is believed to occur due to lack of gravity on the otoliths of the inner ear in space followed by the re-instatement of gravity (to which the otoliths have now become desensitized) back on earth.
In rare cases certain brain conditions may cause motion sickness. Patients with inner ear disorders are more sensitive to any form of motion in general. Anxiety may lead to the development of motion sickness.
The symptoms of motion sickness
Patients may develop only some of the symptoms with brief exposure but with longer exposure may develop all.The following are typical symptoms:
Types of motion sickness.
Motion sickness can be classified according to the sensory stimulation that elicits it. These include:
More commonly however, it is classified according to the environment where it occurs. Although sea sickness and car sickness are the most commonly encountered there are also other types. Other types include:
Testing for motion sickness
There is no specific diagnostic test for motion sickness. Questionnaires such as the “motion sickness susceptibility questionnaire” (MSSQ) may give an indication of a person’s succesptibility for motion sickness.
Another indirect method is to deduct the susceptibility form the magnitude of the evoked vestibular responses. Stronger or prolonged vestibular responses may indicate that a person is more succeptable. This is supported by the observation that airline pilots usually have reduced caloric responses and that persons without a vestibular system generally do not develop motion sickness.
A third way is to use a standardised stimulating motion on a patient and then measure the time it takes for them to become sick. One example of such a test is the “Coriolis sickness sensitivity index”, described by Calkins et al in 1987.
The treatment of motion sickness
Motion sickness is managed by means of preventative behavioural modification, medication, habituation and alternative forms of treatment. The main aim is prevention.
Preventative behavioural modification
This is based on the principle of avoidance and mental activities. The following are worth trying:
Medication works by either suppressing sensory (mainly vestibular) input to the brain or by suppressing central reaction of the brain to the input. Medication should be taken at least 30 minutes before exposure to motion and during motion in order to be effective.
The following medication may be effective:
Habituation is learning strategy whereby a patient is repeatedly exposed to motion. The repeated exposure makes the patient less sensitive to motion. Habituation is usually performed on a rotating chair, centrifuge or in the form of physical exersises.
Alternative forms of treatment
Although Ginger is unlikely to influence the vestibular organ it may prevent vomiting by means of its effect on the stomach. Acupuncture may be an alternative form of treatment.
Sophite syndrome is a variant of motion sickness characterised by yawning, drowsiness, disinclination for work, either physical or mental, and the lack of participation in group activities. Nausea and vomiting are not typically seen. The significance of this disorder is that it may lead to accidents in workers where a high level of concentration is required. It is managed in the same way as conventional motion sickness.