Determinants of Motion Sickness in Tilting Trains: Coriolis/Cross-Coupling Stimuli and Tilt Delay

Reduction of the vertical vestibular-ocular reflex in military aircraft pilots exposed to tactical, high-performance flight

Background

Exposure to high-performance flight stresses the vestibular system and may lead to adaptive changes in the vestibular responses of pilots. We investigated the vestibular-ocular reflex of pilots with different histories of flight exposure both with respect to hours of flight and flight conditions (tactical, high-performance vs. non-high-performance) to evaluate if and how adaptative changes are observable.

Methods

We evaluated the vestibular-ocular reflex of aircraft pilots using the video Head Impulse Test. In study 1, we assessed three groups of military pilots: Group 1 had 68 pilots with few hours of flight experience (<300 h) in non-high-performance flight conditions; Group 2 had 15 pilots with many hours of flight (>3,000 h) and regularly flying tactical, high-performance flight conditions; Group 3 had eight pilots with many hours of flight (>3,000 h) but not exposed to tactical, high-performance flight conditions. In study 2, four trainee pilots were followed up and tested three times over a 4-year period: (1) <300 h of flight on civil aircraft; (2) shortly after exposure to aerobatic training and with <2,000 h of overall flight; and (3) after training on tactical, high-performance aircraft (F/A 18) and for more than 2,000 h of flight.

Results

Study 1: Pilots of tactical, high-performance aircrafts (Group 2) had significantly lower gain values (p < 0.05) as compared to Groups 1 and 3, selectively for the vertical semicircular canals. They also had a statistically (p = 0.022) higher proportion (0.53) of pathological values in at least one vertical semicircular canal as compared to the other groups. Study 2: A statistically significant (p < 0.05) decrease in the rVOR gains of all vertical semicircular canals, but not of the horizontal canals, was observed. Two pilots had a pathological value in at least one vertical semicircular canal in the third test.

Discussion

The results evidence a decrease in the gain of the vestibular-ocular reflex as measured with the video head impulse test for the vertical canals. This decrease appears to be associated with the exposure to tactical, high-performance flight rather than with the overall flight experience.

The neural basis of motion sickness

Although motion of the head and body has been suspected or known as the provocative cause for the production of motion sickness for centuries, it is only within the last 20 yr that the source of the signal generating motion sickness and its neural basis has been firmly established. Here, we briefly review the source of the conflicts that cause the body to generate the autonomic signs and symptoms that constitute motion sickness and provide a summary of the experimental data that have led to an understanding of how motion sickness is generated and can be controlled. Activity and structures that produce motion sickness include vestibular input through the semicircular canals, the otolith organs, and the velocity storage integrator in the vestibular nuclei. Velocity storage is produced through activity of vestibular-only (VO) neurons under control of neural structures in the nodulus of the vestibulo-cerebellum. Separate groups of nodular neurons sense orientation to gravity, roll/tilt, and translation, which provide strong inhibitory control of the VO neurons. Additionally, there are acetylcholinergic projections from the nodulus to the stomach, which along with other serotonergic inputs from the vestibular nuclei, could induce nausea and vomiting. Major inhibition is produced by the GABA_B receptors, which modulate and suppress activity in the velocity storage integrator. Ingestion of the GABA_B agonist baclofen causes suppression of motion sickness. Hopefully, a better understanding of the source of sensory conflict will lead to better ways to avoid and treat the autonomic signs and symptoms that constitute the syndrome.

Effect of Prophylactic Medication on Associated Dizziness and Motion Sickness in Migraine

OBJECTIVE

To determine the efficacy of prophylactic medications for migraine in reducing associated dizziness and motion sickness.

STUDY DESIGN

Multicenter prospective observational study.

SETTING

Nationwide 9 Dizziness Clinics in South Korea.

PATIENTS

One hundred thirty-eight patients who required a preventive medication for migraine accompanied by dizziness and motion sickness.

INTERVENTION

At least one of the prophylactic medications was prescribed among the beta-blockers, calcium channel blockers, tricyclic antidepressants, and antiepileptic drugs.

MAIN OUTCOME MEASURE

For 3 months from the index visit, the patients had monthly assessments of the headache (frequency and duration), dizziness handicap inventory, University of California Los Angeles dizziness questionnaire, vertigo symptom scale, and motion sickness score.

RESULTS

The prophylactic medications significantly improved the headache profiles, all three parameters of dizziness (dizziness handicap inventory, University of California Los Angeles dizziness questionnaire, and vertigo symptom scale), and severity of motion sickness (p < 0.001).

CONCLUSION

The prophylactic medication for migraine also improves associated dizziness and motion sickness as well as the headaches.