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TWO-YEAR RESPONSES OF HEART RATE AND HEART RATE VARIABILITY TO FIRST OCCUPATIONAL LEAD EXPOSURE.

OBJECTIVE
Because of the falling lead exposure, the literature relating autonomous nervous function to blood lead has limited relevance.


DESIGN AND METHOD
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, heart rate variability (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 heart rate variability power and orthostatic heart rate variability responses were derived from 5-minute eletrocardiograms in the supine and standing positions by Fourier transform and autoregression. Blood lead was determined by inductively coupled plasma mass spectrometry.


RESULTS
From baseline to follow-up, blood lead increased from 4.22 to 14.1 ug/dL and supine/standing HR from 63.6/75.5 to 67.1/78.8 beats per minute. In analyses stratified by fourths of blood lead changes, trends in heart rate and Fourier/autoregressive heart rate variability did not reveal a dose-response curve (0.074< = P< = 0.98). In multivariable-adjusted mixed models, heart rate, Fourier/autoregressive heart rate variability, and nerve conduction velocity changes were unrelated to blood lead except for a weak inverse association between supine heart rate and blood lead changes (-0.55%; P = 0.029). The expected associations between heart rate variability and heart rate changes were preserved with no differences at baseline/follow-up. Analyses ichotomised by baseline median blood lead or cumulative blood lead index (4.30 ug/dL or 32.1 ug/dL × year) suggested an heart rate variability increase versus decrease in the low versus high baseline exposure group.


CONCLUSIONS
Thus, a > 3-fold blood lead increment did not affect autonomous neural function as captured by heart rate variability.