A closed-loop mechanical ventilation controller with explicit objective functions

A closed-loop lung ventilation controller was designed, aiming to: 1) track a desired end-tidal CO/sub 2/ pressure (P/sub et/CO/sub 2/), 2) find the positive end-expiratory pressure (PEEP) of minimum estimated respiratory system elastance (E/sub rs,e/), and 3) follow objective functions conjectured to reduce lung injury. After numerical simulations, tests were performed in six paralyzed piglets. Respiratory mechanics parameters were estimated by the recursive least squares (RLS) method. The controller incorporated a modified PI controller for P/sub et/CO/sub 2/ and a gradient descent method for PEEP. In each animal, three automated PEEP control runs were performed, as well as a manual PEEP titration of E/sub rs,e/ and a multiple P/sub et/CO/sub 2/ step change trial. Overall performance indexes were obtained from PEEP control, such as minimum E/sub rs,e/ (37.0+-4.5cmH/sub 2/O.L/sup -1/), time to reach the minimum E/sub rs,e/ (235 +-182 s) and associated PEEP (6.5+-1.0 cmH/sub 2/O), and from P/sub et/CO/sub 2/ control, such as rise time (53 +- 22 s), absolute overshoot/undershoot of P/sub et/CO/sub 2/ (3+-1 mmHg), and settling time (145 +- 72 s). The resulting CO/sub 2/ controller dynamics approximate physiological responses, and results from PEEP control were similar to those obtained by manual titration. Multiple dependencies linking the involved variables are discussed. The present controller can help to implement and evaluate objective functions that meet clinical goals.