The reduced-frequency ring anywhere between 0
The mean power spectrum of CNH rabbits (dotted line, filled circles; n = 8) showed a large reduction of the components at the very low (< 0.2 Hz) and high (> 0.8 Hz) frequency bands, with respect to the mean power spectrum of control rabbits (continuous line, empty circles; n = 11). 2 and 0.5 Hz was increased in CNH rabbits with respect to the mean power spectrum of control rabbits. Inset: mean values, in standardized units (S.U.), of low frequency (LF), high frequency (HF) and LF/HF ratio in control (empty bars) and CNH rabbits (filled bars). *Significantly different from control rabbits; p < 0.05. Dispersion bars: SEM. PSD power spectral density
Research just after severe two-sided vagotomy
In control rabbits, the total power of the spectra remained comparable before and after vagotomy (319.2 ± 72.7 ms 2 vs. 272.0 ± 96.8 ms 2 , control vs. CNH, respectively; p > 0.05). However, the total power was redistributedpared to their pre-vagotomy spectrograms (Fig. 7a), bilateral vagotomy: (i) decreased power in the high-frequency band, 
especially > 0.7 Hz; (ii) increased power slightly in the low frequency band, 0.2–0.5 Hz (Fig. 7b), and (iii) increased power in the very-low-frequency band, < 0.2 Hz (p < 0.01, Fig. 7c). Acute vagotomy did not affect the mean low-frequency peak (0.056 ± 0.002 Hz before and 0.055 ± 0.004 Hz after vagotomy; p > 0.05, Fig. 7c). The mean high-frequency peak decreased from 1.33 ± 0.17 Hz in the intact condition to 0.94 ± 0.22 Hz after denervation (p > 0.05). Thus, the LF band and the LF/HF ratio increased from 0.05 ± 0.01 and 0.11 ± 0.03 to before to 0.07 ± 0.02 and 0.25 ± 0.06 respectively, after bilateral vagotomy (p < 0.05, Fig. 7c).
Power spectra of the R–R intervals of control rabbits (n = 6) before and after bilateral supra-nodose vagotomy. a Before vagotomy, the prominent components of the power spectral density (PSD) occurred in the very-low- (< 0.2 Hz) and high- (0.8–1.7 Hz) frequency bands. b After vagotomy, the power of the very-low-frequency components (< 0.2 Hz) increased, while the high-frequency band decreased. c The mean power spectrum of vagotomized rabbits (filled circles, continuous line) increased in the very-low frequency band compared to that before vagotomy (empty circles), while the power in the high frequency band decreased, nearly absent between 0.8 and 1.7 Hz compared to that before vagotomy. Left inset: mean power spectra of the high-frequency band (0.8–2.0 Hz). Right inset: mean values, in standardized units (S.U.), of low frequency (LF), high frequency (HF) and LF/HF ratio in control conditions (empty bars) and after bilateral vagotomy (filled bars). *Significantly larger than intact condition; p < 0.05. Dispersion bars: SEM. PSD power spectral density
In CNH rabbits, comparing their spectra pre and post vagotomy (Fig. 8), the total power of the spectra increased due to increases in power at very-low- and low- frequency bands (< 0.6 Hz). Average total power of the spectra increased after bilateral vagotomy from 134.7 ± 35.3 ms 2 to 742.3 ± 210.9 ms 2 (p < 0.05). The mean power spectrum increased in peak amplitude of the very-low-frequency band (0.07 ± 0.005 Hz vs. 0.8 ± 0.21 Hz, pre vs. post vagotomy, respectively). Two additional peaks were evident in the low frequency band at 0.3 and 0.4 Hz (Fig. 8b, c). Nevertheless, the power content of the high frequency band (0.6–2.0 Hz) remained small and unaffected by vagotomy (0.39 ± 0.16 ms 2 vs. 0.28 ± 0.05 ms 2 , pre vs. post vagotomy, respectively; p > 0.05; Fig. 8c). Moreover, the LF band and the LF/HF ratio increased from 0.25 ± 0.08 and 0.87 ± 0.37 before vagotomy to 0.54 ± 0.12 and 7.18 ± 3 after vagotomy (p < 0.05; Fig. 8c).
