Motion sickness and otolith asymmetry.

There is a highly scattered inter-individual susceptibility in man to motion sickness. It is discussed whether different masses of otoconias between right and left sides are responsible for a high susceptibility. In order to proof this theory, we measured the otoliths of fish (salmons, trouts, Xiphophorus Helleri; Sumatra barbes) and found big differences in the utricular stones up to 140%. The mass differences of the saccular stones were much smaller. In fish, showing abnormal swimming behavior during off-vertical axis rotation we found big mass differences compared to that of normal swimmers. This difference was only seen in the utricular and not in the saccular stones. We therefore assume, that a big mass difference is one of the factors to trigger motion sickness especially for the high susceptibility to it. The macula utriculi seem to be much more integrated in the vestibular sense than the macula sacculi.     

Biophysical basis for inner ear decompression sickness.

Isolated inner ear decompression sickness (DCS) is recognized in deep diving involving breathing of helium-oxygen mixtures, particularly when breathing gas is switched to a nitrogen-rich mixture during decompression. The biophysical basis for this selective vulnerability of the inner ear to DCS has not been established. A compartmental model of inert gas kinetics in the human inner ear was constructed from anatomical and physiological parameters described in the literature and used to simulate inert gas tensions in the inner ear during deep dives and breathing-gas substitutions that have been reported to cause inner ear DCS. The model predicts considerable supersaturation, and therefore possible bubble formation, during the initial phase of a conventional decompression. Counterdiffusion of helium and nitrogen from the perilymph may produce supersaturation in the membranous labyrinth and endolymph after switching to a nitrogen-rich breathing mixture even without decompression. Conventional decompression algorithms may result in inadequate decompression for the inner ear for deep dives. Breathing-gas switches should be scheduled deep or shallow to avoid the period of maximum supersaturation resulting from decompression.     

Predicting the time of occurrence of decompression sickness.

Probabilistic models and maximum likelihood estimation have been used to predict the occurrence of decompression sickness (DCS). We indicate a means of extending the maximum likelihood parameter estimation procedure to make use of knowledge of the time at which DCS occurs. Two models were compared in fitting a data set of nearly 1,000 exposures, in which greater than 50 cases of DCS have known times of symptom onset. The additional information provided by the time at which DCS occurred gave us better estimates of model parameters. It was also possible to discriminate between good models, which predict both the occurrence of DCS and the time at which symptoms occur, and poorer models, which may predict only the overall occurrence. The refined models may be useful in new applications for customizing decompression strategies during complex dives involving various times at several different depths. Conditional probabilities of DCS for such dives may be reckoned as the dive is taking place and the decompression strategy adjusted to circumstance. Some of the mechanistic implications and the assumptions needed for safe application of decompression strategies on the basis of conditional probabilities are discussed.     

Successful treatment of acute mountain sickness with dexamethasone.

A double blind, randomised, placebo controlled trial of treatment with dexamethasone for acute mountain sickness was performed in the Capanna "Regina Margherita" at an altitude of 4559 m in the Alps Valais. After 12-16 hours of treatment (8 mg dexamethasone initially, followed by 4 mg every six hours) the mean acute mountain sickness score decreased significantly from 5.4 to 1.3, and eight of 17 patients became totally asymptomatic. Mean arterial oxygen saturation rose from 75.5% to 82.0%, and there was a small increase in standard spirometric measurements. In the placebo group none of these variables changed significantly. It is concluded that dexamethasone may be used as emergency treatment for acute mountain sickness to facilitate safe descent to a lower altitude.