Effect of sinoaortic denervation on frequency-domain estimates of baroreflex sensitivity in conscious cats

In animals and humans, baroreceptor modulation of the sinus node in daily life can be studied by identification of the number of sequences in which systolic blood pressure (SBP) and pulse interval (PI) linearly decrease or increase for several beats. It is also studied by power spectral analysis of SEP and PI in regions where their powers are coherent, although, in contrast to the sequence method, whether this frequency-domain method specifically reflects the baroreceptor-heart rate reflex has not been adequately tested. We recorded intra-arterial BP for similar to 3.5 h in eight conscious cats, first intact and then 7-10 days after sinoaortic denervation (SAD). Sensitivity of baroreceptor-heart rate reflex was assessed in 120-s segments by the square: root of the ratio of PI and SEP spectral powers (alpha) in the regions around 0.1 (MF) and 0.3 (RF) Hz, and coherence between PI and SEP spectral powers in MF and HF regions was computed. SAD increased overall SEP variability and reduced PI variability throughout the frequency range examined. SAD markedly reduced (P < 0.01) both alpha-MF (-65.6%) and alpha-HF (-79.9%) and consistently reduced the number of coherent segments [i.e., where coherence (K-2) > 0.5] and average coherence values in the MF region. In the HF region, however SAD did not alter the number of coherent segments, and although average coherence value throughout the HF band was reduced, in restricted portions of the band (different between animals), a high coherence value survived denervation. No significant changes were seen in any measured variables in five sham-operated cats. Thus the frequency-domain method specifically reflects baroreflex modulation of heart rate in the MF region only. In the HF region, in contrast, baroreflex and nonbaroreflex influences on the sinus node both contribute to a variable degree to determination of heart rate responses to BP oscillations. If used to study baroreflex function in daily life, this method should use the coefficient derived from MF data.