Biochemical and electrophysiological study of subjects with a history of past lead exposure

The effects of lead on porphyrin metabolism and peripheral nervous system were studied in a group of 38 subjects who had not been exposed for a period of time, ranging from 3 to 27 years. The mean values for blood lead (PbB), chelated lead(PbUEDTA), and free erythrocyte protoporphyrin (FEP) were found to be significantly higher in the subjects with past lead exposure than in controls. In all cases the neurological examination was negative. The mean values for maximum motor conduction velocity (MMCV) and conduction velocity of the slower fibers (CVSF) of the ulnar and peroneal nerves were found to be significantly lower in the subjects with past lead exposure than in the control group of 23 subjects standardized for age. Signs of partial denervation were present in four cases, with two presenting a decrease of the motor conduction velocity (MCV) as well. No correlation was found between electrophysiological findings and biochemical indicators of dose and effect. The length of exposure showed a significant negative correlation only with the MMCV of the ulnar nerve. A significant difference from controls standardized for age was observed only in subjects with exposure of more than 6 months for all the electromyographic (EMG) parameters. It does not appear that the EMG findings could depend upon modest lead deposits still present in the organism; they should rather give evidence to the permanent effect of alterations that occurred during the prolonged exposure to lead.