Association of Chronic and Current Measures of Lead Exposure with Different Components of Brainstem Auditory Evoked Potentials

Abstract

Current blood lead (PbB) affects brainstem auditory evoked potentials (BAEPs) in children but whether a similar association exists in lead-exposed adults remains unclear. During an investigation of the neurobehavioral effects of occupational lead exposure we performed BAEPs on 359 English- and French-speaking, currently exposed, male, lead smelter workers having a mean (S.D.) age of 41 (9.0) years, employment duration of 17 (7.9) years, PbB of 28 (8.4) μg/dl, working-lifetime weighted average blood lead (TWA) of 39 (11.9) μg/dl, and working-lifetime integrated blood lead (IBL) index of 719 (421.0) μg·year/dl, the latter a measure of cumulative lead dose. BAEPs were performed at a click stimulation of 10 s −1 for 1000 repetitions, at an intensity 75 dB above the threshold of the ear tested. Right-sided latencies for peak waves I, III, and V and the corresponding interpeak intervals (IPI) I–V, I–III, and III–V were chosen for analyses. Age correlated significantly with BAEPs, PbB, TWA, and IBL. Partial correlation analyses adjusting for age found PbB and TWA significantly associated with wave I latency r=0.13, P<0.01 and r=0.11, P<0.05, respectively, and IBL significantly associated with wave III latency r=0.16, P<0.01. The contribution of age, PbB, TWA and IBL to the variances of different BAEPs was assessed using multiple regression analysis. In the regression model of the full group, after the contribution of age, PbB and TWA accounted for significant variance of wave I, Δr 2=1.8, P<0.01 and Δr 2=1.2%, P<0.04, respectively, and IBL accounted for significant variance of wave III latency, Δr 2=2.8%, P=0.00 and I–III interpeak interval, Δr 2=1.4%, P<0.03. Four groups similar in age were created with increasing abnormalities based upon clinical cut-off scores for wave I latency and I–V interpeak interval. PbB, TWA, and IBL were significantly higher in the group with abnormalities of both latency in wave I and IPL I–V. Lead exposure interferes with BAEPs in a dose-dependent manner. Current lead exposure in this population of lead smelter workers preferentially affected conduction in the distal auditory nerve while chronic lead exposure appeared to impair conduction in the auditory nerve and the auditory pathway in the lower brainstem.