Heart rate variability in health and disease.

Beat-to-beat fluctuations in heart rate (HR) or instantaneous HR is mainly determined by activity of the cardiac sympathetic and parasympathetic systems. Despite the need for standardization in methodology to facilitate the interpretation and comparison of results, the data presented in this review clearly show that there are individual differences in heart rate variability (HRV) and that these differences partly reflect differences in the degree of parasympathetic and sympathetic stimulation of the heart. HRV and its spectral components can be easily and noninvasively assessed and can provide valuable information to the occupational physician. Measurements of HRV and the quantification of its spectral components are powerful predictors of cardiovascular morbidity and mortality. Therefore, it may help assess the return to work of patients with ischemic heart disease. Studies in the workplace can also indicate the effects of various stresses of the work environment on such patients and even on asymptomatic workers.