Impact of alignment to gravito-inertial force on motion sickness and cardiopulmonary variables.

INTRODUCTION: In tilting trains partial alignment to the gravito-inertial force (GIF) in the curves seems to be the best tilt compensation to reduce the incidence of motion sickness. We investigated the effect of alignment to the GIF on the development of motion sickness during low-frequency horizontal motion. METHODS: There were 12 healthy subjects who participated. The design was a three-period, single-blind, crossover trial, counterbalanced for order. Cardiopulmonary measurements, Misery SCores (MISC), and questionnaire data (Motion Sickness Susceptibility Questionnaire, Nijmegen Questionnaire for Hyperventilation) were obtained. The stimulus was a sinusoidal movement (0.176 Hz, 0.2 g peak acceleration) on the ESA-sled. The cabin was compensated for 0% (A-0), 50% (A-50), and 100% (A-100) to the GIF. Runs were 1 wk apart. RESULTS: The A-50 condition may delay the development of motion sickness. Based on the survival curves the possible effect seems temporary. However, MISC 2 early in the runs resulted in high positive and negative predictive values for dropout and survival during the runs. No synchronization of the respiratory frequency with the sled motion was observed. There was a significant (P = 0.002) drop in relative end-tidal CO2 levels. DISCUSSION: There seems to be a rationale for partially compensating to the GIF while trying to prevent motion sickness in tilting trains. Sitting comfort is just better than without compensation at all and Coriolis effects are not as nauseating as with complete tilt compensation. Also, a drop in end-tidal CO2 levels might be a sign of pulmonary compensation for the nauseating stimulus.

Respiratory impact on motion sickness induced by linear motion.

Motion sickness incidence (MSI) for vertical sinusoidal motion reaches a maximum at 0.167 Hz. Normal breathing frequency is close to this frequency. There is some evidence for synchronization of breathing with this stimulus frequency. If this enforced breathing takes place over a larger frequency range (0.05-0.8 Hz) and whether this contributes to the high MSI at 0.167 Hz was investigated. Sinusoidal motion (amplitude 0.3 g, frequencies 0.05, 0.1, 0.2, 0.4, and 0.8 Hz) was applied. Nausea with the MISC-scores and respiratory parameters, such as tidal volume, respiratory frequency, end-tidal CO(2) (PetCO(2)), and respiratory minute volume, were measured. Control conditions included rest and the hyperventilation provocation test. The nausea scores were highest at 0.2 Hz. With increasing frequencies the respiratory minute volume increased and the PetCO(2) values decreased. The hyperventilation provocation test did not cause nausea. The main conclusion is that the high MSI at 0.167 Hz is not due to enforced breathing, since enforced breathing still increases with higher stimulus frequencies.

Hyperventilation in a motion sickness desensitization program.

INTRODUCTION: In motion sickness desensitization programs, the motion sickness provocative stimulus is often a forward bending of the trunk on a rotating chair, inducing Coriolis effects. Since respiratory relaxation techniques are applied successfully in these courses, we investigated whether these repetitive trunk movements by themselves may induce hyperventilation and consequently add to the motion sickness. METHODS: There were 12 healthy subjects who participated in our study. In the Baseline condition, subjects sat relaxed on the stationary chair. In the Hypervent condition, subjects performed voluntary hyperventilation (the level was prescribed). In two other conditions subjects rhythmically bent their trunk on a stationary chair (Tilt-Stat condition) and on a rotating chair (Tilt-Rot condition). In all conditions we measured respiratory and cardiovascular activity (heart frequency, tidal volume, end-tidal CO2, and respiration frequency). RESULTS: Of the 12 subjects, 9 had to stop prematurely in the Tilt-Rot condition because of moderate nausea. Except for heart rate in the Tilt-Rot condition, the measured physiological parameters in these subjects in the Tilt-Stat and Tilt-Rot conditions were not statistically different from the Baseline condition. Only in the Hypervent condition were significant differences observed, but no nausea. DISCUSSION: The findings show that hyperventilation is not the main cause of nausea during the Coriolis effects. We conclude that during the pilot desensitization program with Coriolis stimuli, measurement of cardiovascular and respiratory parameters is not necessary; however, in those cases that do not respond to the intervention, we recommend paying attention to respiratory parameters because hyperventilation does occur on an individual basis.

Motion sickness induced by optokinetic drums.

Motion sickness is not only elicited by certain kinds of self-motion, but also by motion of a visual scene. In case of the latter, optokinetic drums are often used and a visual-vestibular conflict is assumed to cause the sickness. When the rotation axis is Earth vertical however, different studies show different results. Here, we propose that visual-vestibular conflicts per se do not cause sickness whereas subjective vertical mismatch theory can reconcile the disparate findings. The theory attributes the nausea induced by horizontal optokinetic stimulation to the subjects self-inducing pseudo-Coriolis by head movement. This highlights the shortcomings of an optokinetic apparatus--that is non-rigid or inaccurately oriented--and the importance of constraining the subject's behavior.

Theoretical considerations on canal-otolith interaction and an observer model.

Subjective vertical orientation, eye and body movements, and motion sickness all depend on the way our central nervous system deals with the gravito-inertial force resolution problem: how to discern accelerations due to motion from those due to gravity, despite these accelerations being physically indistinguishable. To control body or eye movements, the accelerations due to motion should be known explicitly. Hence, somehow gravity should be filtered out of the specific force or gravito-inertial acceleration (GIA, the sum of both accelerations) as sensed by the otoliths, which are the linear accelerometers in the inner ear. As the GIA also changes in a head-fixed frame of reference when the head is rotated, angular motion as sensed by the semicircular canals in the inner ear should also be considered. We present here a theoretical approach to this problem, and show that the mathematical description of canal-otolith interaction is in fact a three-dimensional equivalent of the two-dimensional description given by Mayne in 1974. A simple low-pass filter is used to divide the GIA into a motion and a gravity component. The retardation of the somatogravic effect by concomitant angular motion during centrifugation is shown as a result. Furthermore we show how the canal-otolith interaction fits within the framework of an observer model to describe subjective vertical orientation, eye movement and motion sickness characteristics. To predict a frequency peak in sickness severity, for example, it is necessary to explicitly include the Mayne equation operating both on sensor afferents and in the internal model. From tilt and translation data from centrifugation and horizontal oscillation, as well as from motion sickness data, we conclude that the time constant of the low-pass filter is in the order of seconds instead of tens of seconds as assumed before. Several corollaries are additionally discussed as a result.