Linear modelling analysis of baroreflex control of arterial pressure variability in rats

Abstract

The objective of the present study was to examine whether a simple linear feedback model of arterial pressure (AP) control by the sympathetic nervous system would be able to reproduce the characteristic features of normal AP variability by using AP and renal sympathetic nerve activity (RSNA) data collected in conscious sinoaortic baroreceptor denervated (SAD) rats. As compared with baroreceptor-intact rats (n = 8), SAD rats (n = 10) had increased spectral power (+ 680%) of AP in the low frequency range (LF, 0.0003-0.14 Hz) and reduced power (−19%) in the mid-frequency range (MF, 0.14-0.8 Hz) containing Mayer waves. In individual SAD rats, RSNA data were translated into 'sympathetic' AP time series by using the RSNA-AP transfer function that had been previously characterized in anaesthetized rats. AP 'perturbation' time series were then calculated by subtracting 'sympathetic' from actual AP time series. Actual RSNA and AP 'perturbation' time series were introduced in a reflex loop that was closed by using the previously identified baroreflex transfer function (from baroreceptor afferent activity to RSNA). By progressively increasing the open-loop static gain, it was possible to compute virtual AP power spectra that increasingly deviated from their progenitor spectra, with spectral power decreasing in the LF range (as a result of baroreflex buffering of haemodynamic perturbations), and increasing in the MF band (as a result of increasing transients at the resonance frequency of the loop). The most accurate reproduction of actual AP and RSNA spectra observed in baroreceptor-intact rats was obtained at 20-30% of the baroreflex critical gain (open-loop static gain resulting in self-sustained oscillations at the resonance frequency). In conclusion, while the gain of the sympathetic component of the arterial baroreceptor reflex largely determines its ability to provide an efficient correction of slow haemodynamic perturbations, this is achieved at the cost of increasing transients at higher frequencies (Mayer waves). However, the system remains fundamentally stable. In freely moving rats, sympathetic nerve activity (SNA) and arterial pressure (AP) show parallel increases during the performance of common behaviours (Miki et al. 2003). In chronically sympathectomized rats, the same behaviours are accompanied by falls rather than increases in AP (Julien et al. 1990;Ferrari et al. 1996), which indicates that behaviourally coupled changes in SNA are effectively responsible for AP changes in the intact animal. From these simple observations, a tight coupling between AP and SNA variabilities would be expected. However, this is not the case. Using frequency-domain approaches, it was found that AP and SNA are correlated in a narrow frequency band (0.4 ± 0.2 Hz in rats). This band, usually referred to as the mid-frequency band, contains the so-called AP Mayer waves (Brown et al. 1994). The correlation (or coherence) between AP and SNA at lower frequencies, where the bulk of AP variability is concentrated, is either weak or incon...

Baroreflex sensitivity, blood pressure buffering, and resonance: what are the links? Computer simulation of healthy subjects and heart failure patients

“…Figure 3C illustrates the principle that a negative-feedback control system with feedback delay buffers the controlled variable at certain frequencies at the cost of resonance at other frequencies. The baroreflex blood pressure control system as simulated in this study behaves in a way that is very similar to what was experimentally observed (10). Blood pressure buffering, a major function of the baroreflex, occurs at frequencies below the Mayer waves (resonance in the LF band, Fig.…”

“…Resonance in blood pressure (5,8,12,31,49) manifests in the form of the well-known Mayer (22,33) waves (beat-to-beat blood pressure oscillations with a frequency of ϳ0.1 Hz/period of ϳ10 s). Effective baroreflex blood pressure buffering occurs below the Mayer frequency (10,16).…”

Baroreflex control of renal sympathetic nerve activity during air-jet stress in rats

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Synergism of Hydrochlorothiazide and Nifedipine on Blood Pressure Variability Reduction and Organ Protection in Spontaneously Hypertensive Rats

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