Urinary PAH metabolites and HRV indices of the workers in different groups.

HF, high frequency; LF, low frequency; rMSSD, root mean square of successive differences in adjacent NN intervals; SDNN: standard deviation of NN intervals; TP: total power.*Simple linear regression for the trend of urinary PAH metabolites with the exposure levels.†Multivariate linear regression for the trend of HRV with the exposure levels with adjustment for age, sex, working years, smoking status, alcohol use, BMI, exercise and hypertension.