RESUMO
Frequency domain analysis of heart rate variability (HRV) is used for the evaluation of autonomic activity. Non-linear domain parameters from HRV are also considered useful. However, properties of the latter have not yet been clearly characterized. Therefore, we studied the relationships among the frequency domain and non-linear parameters from HRV. Continuous Holter electrocardiographic monitoring was conducted on 43 healthy female medical staff including laboratory technologists and nurses during an 8-hour working period in our hospital. Low and high frequency components (LF and HF, respectively) of the frequency domain, recurrence rate (REC%) on recurrence plot analysis, scaling exponents al and a2 on detrended fluctuation analysis, and approximate entropy (ApEn) were obtained from HRV. Both the LF/HF ratio and HF were correlated with al and ApEn. REC% was correlated with ApEn and alpha2, whereas alpha2 was correlated only with REC%. Although autonomic parameters from the frequency domain are closely related with some of the non-linear parameters, it is suggested that a2 and REC% reflect different physiological activities.