Dynamic performance and stability of cerebral ischemic pressor response

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Abstract
A servoanalytic dynamic performance analysis of the cerebral ischemic pressor response has been made by the frequency response method applied to a linearized ischemic response system. Using an isolated perfused head preparation, the cerebral perfusion pressure was changed sinusoidally with a fixed amplitude of 5 mm Hg, but with varied periods ranging from 320 to 20 sec. The systemic arterial pressure waves caused by these input sinusoidal pressure waves were compared with the latter in terms of amplitude ratio and phase shift relationships. As the mean cerebral perfusion pressure was lowered toward zero, the response increased both in gain and phase lag. When these data were plotted as a vector locus on polar coordinates, the locus encircled the –1 point at 180° clockwise in 10 of 16 dogs. In two others, the locus approached very close to the –1 point. Thus, the nature of the cerebral ischemic pressor response was found to be unstable enough to go into self-oscillation under proper closed-loop conditions.