Baroreflex modulation of blood pressure and heart rate variabilities in rats: assessment by spectral analysis.

The role of the baroreflex in the spectral characteristics of mean arterial pressure (MAP) and heart rate (HR) was investigated in 12 control rats and 9 rats with chronic sinoaortic baroreceptor denervation (SAD) during 1) basal conditions and 2) ganglionic blockade with chlorisondamine and restoration of the basal MAP level. In SAD rats, power spectral density of MAP, estimated by a fast Fourier transform, was reduced in the low-frequency (LF, 0.27- to 0.74-Hz) band. Ganglionic blockade highly decreased LF power spectral density of MAP in control rats. No relationship was found between the MAP response to chlorisondamine, taken as an index of the sympathetic vasomotor tone, and the basal LF power spectral density. Transfer function analysis between MAP and HR showed that, in control rats, coherence was high for frequencies surrounding the LF and high-frequency peaks. In SAD rats, coherence was abolished in the LF band but maintained in the high-frequency band. In conclusion, approximately 80% of the LF power spectral density of MAP depends on the sympathetic nervous system activity, and the baroreflex accounts for one-half of this power and for the coherence between MAP and HR oscillations in the LF band.