Abstract

Nine healthy male volunteers were exposed to m-xylene for four hours a day, three hours in the morning and one hour in the afternoon, with a 40 minute break in between, at six day intervals during six succeeding weeks to explore the effects of m-xylene on the sense of balance. The atmospheric m-xylene concentrations were either fixed at 8.2 mumol/l (200 ppm) or they fluctuated (5.2-16.4 mumol/l; 135-400 ppm) with peaks of 16.4 mumol/l and duration of 10 minutes at the beginning of each exposure session. The subjects were sedentary or exercised at 100 W for 10 minutes at the time of the peaks. The two control days, with and without exercise, were similar to the exposure days but without exposure. Body sway was measured with the subjects' eyes open and closed before they entered the chamber and in the chamber immediately after the cessation of the peak exposure when blood samples for gas chromatographic analysis were also drawn. Changes in the eyes closed/open ratio of the average and maximal body sway along the sagittal and lateral axes were calculated using the morning value as a reference. Changes in the eyes closed/open ratios of both average and maximal body sway correlated positively with blood m-xylene concentrations during fixed (8.2 mumol/l) exposure at rest and during fluctuating exposure combined with exercise as analysed with linear regression analysis. The results suggest that m-xylene has a dose related effect on the sense of balance at moderate atmospheric levels.