A Model for Design of a Blood Pressure Controller for Hypertensive Patients

Abstract

Various closed loop control systems have been used to automate the infusion of the drug sodium nitroprusside for treatment of elevated blood pressure frequently observed in the early hours following open heart surgery. Clinical experience indicates a need for an improved controller which adapts to each patient and his changing condition. For system design, analysis, and evaluation, a model of the essential aspects of the arterial blood pressure and its response to nitroprusside is necessary. The model was structured using patient measurement data together with a priori knowledge of physiological concepts and the pharmacological action of the drug. The arterial pressure is considered the sum of nonstationary stochastic background activity and a change due to the nitroprusside (characterized by a transfer function). The model was applied to the simulation of a clinically used controller and has provided insight into responses observed in the treatment of over 700 patients. The model is presently being used for computer-aided design and evaluation of an adaptive controller. Simulations of a preliminary adaptive transient controller and regulator demonstrated improved performance over the clinically used controller.