Fig. 1.

Closed-loop drug infusion system for automated hemodynamic resuscitation in septic shock. a Block diagram of the system for simultaneous control of mean arterial pressure (AP) and cardiac output (CO) in septic shock. AP* and CO* represent target AP and target CO, respectively. From these target variables, target values of systemic arterial resistance (R*) and stressed blood volume (V*) are determined (red rectangle). Subject’s R, V, and Frank-Starling slope of the left ventricle (S) are calculated from AP, CO, central venous pressure (CVP) and pulmonary wedge pressure (PWP) (blue rectangle). The proportional-integral controller adjusts infusion rate of noradrenaline (NA) to minimize the difference between R and R* (green rectangle). A non-linear controller adjusts infusion of Ringer’s acetate (RiA) to minimize the difference between V and V* (orange rectangle). b Block diagram of the proportional-integral controller. Ki and Kp represent the integral and proportional gain constants, respectively. s is a Laplace operator