Power spectral analysis of heart rate variability for assessment of diurnal variation of autonomic nervous activity in miniature swine

Background and Purposes: The purpose of the study was to document diurnal variation of autonomic nervous functions by use of power spectral analysis of heart rate (HR) variability. Methods: To clarify characteristics of power spectral analysis of HR variability, electrocardiogram (ECG), blood pressure (BP), and respiratory (Resp) waveform simultaneously were recorded. Results: Two major spectral components were examined at low (LF)- and high (HF)-frequency bands for HR variability. Coherence between HR and Resp variabilities and HR and BP variabilities was maximal at approximately 0.14 and 0.03 Hz, respectively. On the basis of these data, two frequency bands of interest-LF (0.01 to 0.07 Hz) and BF (0.07 to 1.0 Hz)-were defined. Autonomic blockade studies indicated that the parasympathetic system mediated the HF and LF components, whereas the sympathetic system mediated only the LF component; HR had a diurnal pattern. The LF and HF bands in the dark phase tended to be higher than those in the light phase. The LF-to-HF ratio had a diurnal pattern similar to that of the HR, Conclusion: Parasympathetic nervous activity in miniature swine may be predominant in the dark phase. The characteristics of power spectra and diurnal variations of autonomic nervous functions are almost the same as those of humans. Therefore, miniature swine may be a useful animal model for future biobehavioral and pharmacotoxicologic studies.