Biphasic effects of inhaled solvents on human equilibrium.

Nine healthy male students were exposed for 4 hours at 6-day intervals to atmospheric concentrations of m-xylene (8.2 mumol/l; 200 p.m.) and 1,1,1-trichloroethane (TCE) (8.2 and 16.4 mumol/l; 200 and 400 p.m.) and also to a combination of 8.2 mumol/l of xylene and of 16.4 mumol/l of TCE. The exposures took place during 6 consecutive weeks. Body sway was recorded with the subjects' eyes closed and open on each day with a strain gauge transducer platform prior to and during the exposures. For the average and for the maximal body sway, the ratio of the sway with the eyes closed to the sway with the eyes open was calculated for each recording. Xylene and TCE at 8.2 mumol/l in air tended to decrease the ratio, whereas the higher TCE concentration alone or in combination with xylene tended to have an opposite effect of the same magnitude. The results support the idea that TCE might exhibit a biphasic pattern of acute effects on the central vestibular system. Pharmacokinetic interactions between xylene and TCE were not observed.