Two-Year Responses of Heart Rate and Heart Rate Variability to First Occupational Lead Exposure

Abstract

Because of the falling lead exposure, the literature relating autonomous nervous function to blood lead (BL) has limited relevance. In the longitudinal Study for Promotion of Health in Recycling Lead (URL: https://www.clinicaltrials.gov ; Unique identifier: NCT02243904), we recorded the 2-year responses of heart rate (HR), HR variability (HRV; Cardiax, International Medical Equipment Developing, Budapest, Hungary), and median nerve conduction velocity (Brevio, NeuMed, West Trenton, NJ), a routine test in occupational medicine, to first lead exposure in 195 newly hired workers (91.3% men; mean age, 27.8 years). High- and low-frequency HRV power and orthostatic HRV responses were derived from 5-minute ECGs in the supine and standing positions by Fourier transform and autoregression. BL was determined by inductively coupled plasma mass spectrometry. From baseline to follow-up, BL increased from 4.22 to 14.1 μg/dL and supine/standing HR from 63.6/75.5 to 67.1/78.8 beats per minute. In analyses stratified by fourths of BL changes, trends in HR and Fourier/autoregressive HRV did not reveal a dose-response curve (0.074≤ P ≤0.98). In multivariable-adjusted mixed models, HR, Fourier/autoregressive HRV, and nerve conduction velocity changes were unrelated to BL except for a weak inverse association between supine HR and BL changes (−0.55%; P =0.029). The expected associations between HRV and HR changes were preserved with no differences at baseline/follow-up. Analyses dichotomized by baseline median BL or cumulative BL index (4.30 μg/dL or 32.1 μg/dL×year) suggested an HRV increase versus decrease in the low versus high baseline exposure group. Thus, a >3-fold BL increment did not affect autonomous neural function as captured by HRV.