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1 Department of Behavioral Science, 2 The Neuroscience Program, 3 Department of Surgery, Artificial Organs, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
To determine the
relationship between blood pressure (BP) variability and the open-loop
frequency domain transfer function (TF) of the baroreflexes, we
measured the pre- and postsinoaortic denervation (SAD) spectra and the
effects of periodic and step inputs to the aortic depressor nerve and
isolated carotid sinus of central nervous system-intact,
neuromuscular-blocked (NMB) rats. Similar to previous results in freely
moving rats, SAD greatly increased very low frequency (VLF)
(0.01-0.2 Hz) systolic blood pressure (SBP) noise power. Step
response-frequency measurements for SBP; interbeat interval (IBI);
venous pressure; mesenteric, femoral, and skin blood flow; and direct
modulation analyses of SBP showed that only VLF variability could be
substantially attenuated by an intact baroreflex. The 
3-dB frequency
for SBP is 0.035-0.056 Hz; femoral vascular conductance is similar
to SBP, but mesenteric vascular conductance has a reliably lower and
IBI has a reliably higher 3-dB point. The overall open-loop
transportation lag, of which 
0.1 s is neural, is 
1.07 s.
Constrained algebraic solution, over a range of frequencies, of the
pre- and postSAD endogenous noise spectra and the independently
determined relative frequency and absolute lag measurements was used to
calculate the absolute gain for the open-loop TF. The average gain at
0.02 Hz, the frequency of maximum sensitivity, was 1.47 (95%
confidence interval = ±0.48), which agrees well with estimates for the
dog reversible sinus. We found that, in the NMB rat, the effects of SAD
on the BP noise spectrum were accounted for by the open-loop properties
of the baroreflex.
baroreceptors; carotid sinus; aortic depressor nerve; systems analysis; transfer function; noise
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