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1 Departments of Physiology and Electrical and Electronic Engineering, University of Auckland, Auckland, New Zealand; and 2 Department of Electronic Engineering, National University of Ireland, Maynooth, Ireland
The aim
in the present experiments was to assess the dynamic baroreflex control
of blood pressure, to develop an accurate mathematical model that
represented this relationship, and to assess the role of dynamic
changes in heart rate and stroke volume in giving rise to components of
this response. Patterned electrical stimulation [pseudo-random binary
sequence (PRBS)] was applied to the aortic depressor nerve (ADN) to
produce changes in blood pressure under open-loop conditions in
anesthetized rabbits. The stimulus provided constant power over the
frequency range 0-0.5 Hz and revealed that the composite systems
represented by the central nervous system, sympathetic activity, and
vascular resistance responded as a second-order low-pass filter (corner
frequency 
0.047 Hz) with a time delay (1.01 s). The gain between ADN
and mean arterial pressure was reasonably constant before the corner frequency and then decreased with increasing frequency of stimulus. Although the heart rate was altered in response to the PRBS stimuli, we
found that removal of the heart's ability to contribute to blood
pressure variability by vagotomy and 
1-receptor blockade did not significantly alter the frequency response. We conclude that
the contribution of the heart to the dynamic regulation of blood
pressure is negligible in the rabbit. The consequences of this finding
are examined with respect to low-frequency oscillations in blood pressure.
sympathetic nerve activity; modeling; transfer function; vasculature; rabbit
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