Assessment of Autonomic Neurotoxicity of Environmental and Occupational Factors as Determined by Heart Rate Variability: Recent Findings.

The measurement of heart rate variability (coefficient of variation of ECG R-R intervals) provides a promising approach for the objective assessment of the autonomic nervous function. It is noninvasive and clinically practical, although it tends to be distorted by confounding factors such as age, tobacco and alcohol. In particular, two components of the respiratory sinus arrhythmia with a high frequency (HF) of 0.15-0.4 Hz and Mayer wave related sinus arrhythmia with a low frequency (LF) of 0.04-0.15 Hz in the heart rate variability, which were computed by autoregressive spectral and component wave analyses, reflect parasympathetic and sympathetic activities, respectively. This article is intended to present an overview of research, utilizing this frequency domain method, in environmental and occupational health. The available literature, addressing the impact of some chemicals and work-related factors on the human autonomic nervous system, indicates that parasympathetic activity appears to be more vulnerable to these factors than does sympathetic activity. Since decreased cardiac vagal tone is associated with an increased risk of sudden cardiac death or coronary heart disease, attention should be directed to further discovery of hazardous factors in the environment and workplace, which may pose potential autonomic neurotoxic risks.