This article addresses the issue of knowledge representation and reasoning techniques used in the design of a ventilator controller. It presents two approaches: a model-based approach that uses domain models and corresponding reasoning techniques, and a goal-oriented approach combining associative and procedural knowledge in implementing 'compiled' experience-based response of an expert and usage of more conventional reasoning techniques. The approaches are discussed in the context of data provided for this symposium. In the last section we will describe the basic architecture of a controller that is under the development in our lab and that will eventually implement a goal-directed approach. Its development is based on the conjecture that the goal-directed approach is capable of efficiently solving nontrivial portion of the control problem without large increases in the complexity of the knowledge.