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The intent of this research was to provide a theoretical approach for the optimal adjustment of controlled ventilators used in treating respiratory insufficiency in critically ill patients who have undergone major thoracic or abdominal surgery. In order to solve the optimization problem, it was necessary to develop a mathematical description of the process. The number of interactions involved, as well as the changing nature of the actual system, has been represented by an extremely complex model which may defy solution (Guyton 1973, Grodins 1967). It was therefore decided to describe the respiratory plant by a simple mathematical model that includes the pertinent information regarding the performance of the actual gas transport process. Variations in plant parameters were taken into account by providing an adaptive control philosophy that involves resolving the optimization problem (Sage 1966) to determine the following optimal ventilator settings: 1) tidal volume, 2) respiratory frequency and 3) fraction of inspired oxygen. |
