Date of Award

Spring 2000

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering - (Ph.D.)

Department

Electrical and Computer Engineering

First Advisor

Stanley S. Reisman

Second Advisor

Barry R. Dworkin

Third Advisor

Alan Snyder

Fourth Advisor

Alexander Haimovich

Fifth Advisor

Peter Engler

Abstract

The baroreflex is one of the most important feedback systems in the body to maintain blood pressure variation within the homeostatic range. In this dissertation, the important features of the carotid and aortic baroreflexes have been extensively investigated on ventilated, central nervous system intact, neuromuscular blocked (NMB) rats using different control system and signal processing tools. Studies have demonstrated that sinoaortic denervation (SAD) caused substantial increases in the blood pressure variability. Comparing the pre- and post-SAD blood pressure spectra, there was a significant increase of power in the very low frequency region (0.00195 -0.2 Hz), and a significant decrease of power in the low frequency region (0.2 - 0.6 Hz) after SAD. The dominant power change after SAD was in the very low frequency region of the blood pressure spectra.

The carotid and aortic baroreflexes were accessed by volumetric manipulation of the carotid sinus and electrical manipulation of the aortic depressor nerve (ADN) using step and sinusoidal stimulations. Myelinated ADN-A fibers and myelinated + unmyelinated ADN-A+C fibers were accessed separately in the experiments. Results showed that the baroreflex functions as a 'low-pass' filter, with -3dB cutoff frequency at approximately <0. I Hz. The major working area of the baroreflex system is in the VLF region of the blood pressure spectra. The estimated system transportation lag was 1.07s, which would cause the baroreflex system to oscillate at frequencies around 0.4 Hz.

Analyses demonstrated that it is not likely that the baroreflex is activated only occasionally, such as in response to postural shifts, but operates continuously to bring the blood pressure into balance. It is theoretically and experimentally demonstrated that the absolute gain of the open-loop baroreflex system can be predicted by the ratio of the pre-and post- blood pressure amplitude spectra.

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