To evaluate the effects of blood and nerve lead (BPb, NPb) concentrations on peripheral nerve conduction velocity (NCV), we measured maximal motor nerve conduction velocity in the sciatic nerve and its posterior tibial branch in forty 21-week-old male Wistar rats, which were given drinking water containing lead acetate at concentrations of 0.1, 0.5, 1.0 and 2.0% for 15 weeks (lead groups, ten rats for each dose); and in ten sex-and age-matched Wistar rats (control group), which were given drinking water free of lead acetate for the same period. NCV and BPb were significantly different between the rats given the smallest dose of lead acetate (0.1%) and the control group (p<0.05) while, on the other hand, no significant differences in NPb and body weight (BW) were observed between the two groups (p>0.05). With further increases in the dose of lead acetate, no significant changes were found in NCV and BW in each lead group; NPb was significantly higher in the 0.5% than in the 0.1% lead group. NCV was significantly correlated with BPb in all the fifty rats examined (lead and control groups combined, p<0.05), but not correlated with NPb and BW. These results suggest that the alteration in NCV is closely related to the change in BPb; NCV decreases most markedly at a lower level of BPb and the diminution rate of NCV decreases progressively as BPb increases.
The purpose of this study was to apply psychophysical principles to establish the optimum work rate during load transportation on the head and by yoke. The metabolic and perceptual responses of 10 male students of average aerobic capacity (3.67±0.77 ιmin-1) were monitored while carrying external loads (11.6, 16.1 and 20.6 kg) at varying speeds (3.2, 4.4 and 5.6 km•hr-1) on a level motor-driven treadmill using the headpack and the transverse yoke modes of load carriage. The physiological and perceptual responses for the 2 modes of load car-riage were not statistically different (p>0.05). As such, the values for the 2 modes were averaged. In order to identify the optimum rate of work, the mean oxygen uptake (VO2), local ratings of perceived exertion and the overall body exertion were plotted against the walking speeds. The optimum work rate estimated by physiological (40% VO2max) criteria was higher than that by perceptual (RPE=12 on Borg's 15-point category scale) criteria. The findings suggest the need to take into consideration the subjective feelings of exertion in addition to the work rate conditions that elicit 40 VO2max when prescribing standardsf or external load transportation.
Male rats were exposed to four different concentrations of methyl bromide for 4 hrs/day ; 150 ppm for 11 weeks, 55 times, and to 200, 300, and 400 ppm for 6 weeks, 30 times. Changes in body weight, general condition and hema-tology, changes in organ weight, residual bromide ion concentration, and histopa-thology of several organs were studied. Suppression of body weight increment, abnormal clinical signs and severe weakness were found in the highly exposed group. Bromide ion accumulation was seen especially in the kidney and spleen, without significant dose-related change. Remarkable changes appeared histopathologically in the brain and heart. Necrosis was exhibited zonally from the first to fourth layers of the dorso-external cortex bilaterally, showing a spongy, edematous and hyperemic appearance, accompanied by proliferation of blood vessels. This bilateral lesion had spread selectively to basal nuclei and brain stem. Multiple, small focal necroses were found in wide regions of the heart. Necrosis of the brain and heart, both of which have high sensitivity to oxygen defficiency, was thought to be caused by the longterm hypoxic condition as manifested in the histopathological findings.