Some Pearls and Pitfalls about Motion Sickness
By Dr. William A. Bateman, Senior Medical Consultant
The term ‘motion sickness’ is a bit of a misnomer: it isn’t really due to ‘motion’ per se, and it isn’t really a ‘sickness’ in the disease sense of the term. It nevertheless gets used to describe a whole host of syndromes, more accurately referred to as ‘motion adaptation syndromes’. Seasickness, airsickness, and car-sickness are all common examples. Other less-commonly-heard-of entities include space-sickness (experienced in at least some form by at least two-thirds of astronauts), simulator sickness (very common even in experienced pilots during and after simulator flights), and ‘disembarkation syndrome’ (unsteadiness commonly experienced after coming ashore following being at sea for a couple of days).
The unifying feature of all these phenomena is a disconnect between what your senses are telling you, the most common being the visual and vestibular (balance) systems. In airsickness, for example, your vestibular system tells you that you are moving all over the sky but your visual system tells you that you are NOT (since everything around you in the aircraft cabin is moving the same as you are, and so seems stationary with respect to you). However, it makes no sense for someone to feel nauseated and perhaps vomit in response to motion – why on earth would that be a helpful thing for human beings to do?
One theory is that motion sickness is really just a manifestation of a hierarchy of countermeasures against poisoning. The first level is smell & taste: if something smells or tastes bad when you eat it may be tainted, so vomiting would make sense. The second involves the irritation of the stomach-lining: too much alcohol, for example will irritate the stomach, so vomiting to get rid of excess alcohol also makes sense. The third level involves chemoreceptors in the brain that can recognize certain poisons in the bloodstream: this is how ipecac (used in certain poisoning victims) works to induce vomiting. A final step may be a ‘self-diagnostic’ that monitors brain inputs and outputs to see if they make sense: it could be that we have been designed to say, “…my balance tells me I’m moving, but my eyes tell me I’m NOT, which makes no sense – so my brain isn’t working right, I must’ve been poisoned, so I better vomit!”
While all this may seem only of academic interest, it does help explain our abysmal success in ‘treating’ motion sickness: all medications used to treat it really may just be acting as sedatives to blunt this final ‘self-diagnostic’ mechanism – which would be understandably hard to overcome. Accordingly ALL these medications are unwise to use in jobs or pastimes requiring unimpaired vigilance (eg, machine operators, pilots, and SCUBA divers).
Highlights of some commonly-used motion sickness interventions are as follows:
- Over-the-counter (OTC) agents. Gravol (dimenhydrinate) & Bonamine (meclizine) are widely-used ‘first-steps’ which generally cause sedation and whose beneficial (and adverse) effects vary widely between individuals. Transderm V (scopolamine patch) can be effective and well-tolerated for trips lasting over a day or so, but has a long list of precautions and warnings (eg, not for use in children, those with glaucoma, urinary obstruction problems; use only with extreme caution in those over 65, etc).
- Acupressure wrist-bands. These have not been shown to be convincingly effective, but some find them helpful.
- Prescription agents. Histanil (promethazine) together with dextroamphetamine (to blunt sedation) is probably the most effective combination around, but can sometimes be hard to obtain because of the latter’s restricted drug status.
- Desensitization. Motion sickness desensitization programs have limited success in certain populations (eg, Canadian Forces pilot trainees), but have been shown not to have any value in cross-adaptation. That is, since motion-sickness is known to be very ‘motion-specific’, those desensitized to airsickness are unlikely to show any reduction in seasickness.
Practical Tips to Prevent Motion-Sickness:
‘Keep your eyes on the horizon’ and avoidance of reading (both of which make sense in view of the visual-vestibular disconnect theory mentioned above). Motion sickness can be contagious, so try to stay away from other motion-sickness sufferers! Other such tips can be found here.
Details of these and other treatments for motion sickness can be found here.
Individually-tailored interventions can be obtained and prescribed at Medcan’s Travel Clinic.
To book an appointment for the Medcan Travel Clinic or for any of our other services please contact our bookings team at 416.350.5900 or email to bookings@medcan.com