Objectives To study the impact of respiratory frequency on HRV and discuss how to exclude it.
Methods 12 healthy male rabbits aged 4-5 months and weighting 2.5-3.0 kg were selected. The Rabbits respiratory control system was established. ECG, instant blood pressure and respiratory waveform under different respiratory frequency (RF) (40 bpm,50 bpm,60 bpm) were recorded synchronously via SKY-A4 (a three channel electrophysiolograph); HRV & BRS2.0-a HRV analysis system was used to observe the shift of high frequency peak (HFP), and to analyse power spectra density (PSD). Two different analysis methods were adopted to analyse PSD, tHRV (traditional heart rate variability) analysis method with which parameters of different frequency segment were preset; EHRV (enhance heart rate variability) analysis method with which very low frequency were filtered, and HF were located near Fundamental Respiratory Frequency (FRF). Comparisons between the results of the two methods were made.
Results The shift of HFP: RF 50 bpm, the HFP was located at the conjunction of LF segment and HF segment; RF 40 bpm, HFP would be shifted into the LF segment; RF 60 bpm, the total HFP would be shifted into HF segment. Comparison between tHRV and eHRV results: tHRV results:compared with RF 50 bmp, RF 40 bpm HF, HFnorm were decreased, LF, LFnorm, LF/HF were increased; RF 60 bpm seems increase HF (t =-3.477, P = 0.005), HFnorm (t =-2.903, P = 0.013), decrease LF/HF (t = 2.500, P = 0.028). eHRV results: there was no significant difference was fund between different RF PSD.
Conclusions RF slow down would shift HFP to relatively low frequency, sometimes to LF segment, which would increase LF and decrease HF. Enhanced HRV analysis could exclude this influence.