Quantification of neuromotor function for detection of the effects of manganese

The effect of low level exposure to manganese (Mn) was examined in 297 subj ects from southwest Quebec. Blood manganese (MnB) levels as well as other p ossibly relevant variables were obtained. We tested equipment and analysis procedures that we have developed to quantify aspects of motor function tho ught to be affected by exposure to toxins, in particular, rapid alternating movements, rapid and precise pointing movements, and tremor. (1) The euryt hmokinesimeter measures timing and precision of contacts between a hand-hel d stylus and a pair of metal targets (proximal/distal). This roughly approx imates the finger-to-nose test of the UPDRS. Characteristics quantifying sp eed, precision and regularity of the movements were calculated, as well as multiple contacts due to tremor and an index based on Fitts' Law eliminatin g the effect of the trade-off between speed and precision. (2) The diadocho kinesimeter accurately measures rapid rotation of the forearms (pronation/s upination). Characteristics quantifying the range, speed, period, shape and regularity of the oscillatory movements were calculated, as well as the sm oothness of the movement on a fine scale and the coordination between the t wo hands. (3) Postural tremor of the arm and hand was measured using the ac celerometry-based "TREMOR" system of Danish Product Development. We used th e amplitude and frequency characteristics provided by the TREMOR system: in tensity, center frequency, dispersion and harmonic index. Previous studies have shown that these tests are sufficiently sensitive to detect sma II dif ferences in performance of different groups of subjects, with indications t hat some characteristics are also specific to particular conditions. In thi s study, significant though small effects related to age and gender were fo und in many of the characteristics. When effects of other variables are rem oved, low-level exposure to Mn was found to be associated with a decrease i n ability to perform regular, rapid and precise pointing movements, a decre ase in ability to attain high maximum rotation speeds in rapid alternating movements, and an increase in regularity of tremor oscillations. Moreover, the effects are age-related for levels of MnB 7.5 mu g/L. (C) 1999 Inter Pr ess, Inc.