computer methods and programs in biomedicine 89 ( 2 0 0 8 ) 153–161 journal homepage: www.intl.elsevierhealth.com/journals/cmpb The benefits of using Guyton’s model in a hypotensive control system Chi-Ngon Nguyen a,b , Olaf Simanski b,* , Ralf K ¨ ahler b , Agnes Schubert b , Matthias Janda c ,J¨ orn Bajorat c , Bernhard Lampe b a Department of Telecommunications and Control Engineering, Cantho University, 92100 Cantho, Vietnam b Department of Computer Science and Electrical Engineering, University of Rostock, 18119 Rostock, Germany c Clinic of Anesthesiology and Intensive Care, University of Rostock, Schillingallee 55, 18055 Rostock, Germany article info Article history: Received 29 December 2006 Received in revised form 14 February 2007 Accepted 7 March 2007 Keywords: Blood pressure Fuzzy control Physiological model Medical systems Medical applications abstract In order to improve the intraoperative applications, this paper presents the advantages of using Guyton’s model in hypotensive control system development. In this system, the mean arterial pressure is decreased and maintained at a low level during anaesthesia by control- ling sodium nitroprusside infusion rate. The key of the study is to develop a physiological model of cardiovascular dynamics to present the mean arterial pressure response to sodium nitroprusside, which was considered as a linear model in most of known blood pressure control systems. Being linear, the previous models cannot accurately mimic a physiological system of human circulation, especially at deep hypotensive control with strong reaction of the body. The enhanced model in this study was modified based on Guyton’s model of human circulation. It is useful to design a PID controller, which allows studying and han- dling the wide range of the body sensitivities. This model is also helpful for studying the behaviors of patients under anaesthesia conditions, such as the perfusion of organs and the reaction of the body at hypotensive state. A fuzzy gain scheduler and a supervising algorithm were also developed for online tuning the controller to handle the behavior of the body. The control system was tested on 25 experiments on seven pigs in the animal laboratory. Simulation and experiment results proved the usefulness of Guyton’s model in control system design which can present the dynamical response of blood pressure in the circulation under and after hypotensive control. The results also indicated the safety and stability of the controller. © 2007 Elsevier Ireland Ltd. All rights reserved. 1. Introduction In medical applications, maintaining the mean arterial pres- sure (MAP) at a low level has several advantages. During cardiac surgery, it can limit intraoperative bleeding, which causes a lot of side effects, such as increased risk of sepsis and organ failure [1–3]. In postsurgery at Intensive Care Unit, it can promote healing, especially after cardiac surgery [4–6]. Since ∗ Corresponding author. Tel.: +49 381 498 7706; fax: +49 381 498 7702. E-mail address: olaf.simanski@uni-rostock.de (O. Simanski). sodium nitroprusside (SNP) became commercially available in 1974, this drug has been used in the treatment of hyperten- sion [7,8]. However, automatic control of blood pressure (BP) is required to handle the wide range of patient sensitivity to the drugs because an overdose of SNP may cause toxic side effects [5,9]. When used and designed properly, the automatic control systems can improve the quality of patient care and also reduce the amount of work for physicians and nurses [7]. 0169-2607/$ – see front matter © 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.cmpb.2007.03.005