Konstruktion av patientsimulator för anestesimaskiner
A patient simulator for testing anaesthesia machines has been developed at Maquet Critical Care AB, to reduce costly and time-consuming experiments on animals. The device simulates human lungs regarding lung dynamics and volume, uptake of anaesthetic agents and the production of carbon dioxide, heat and moisture. Further demands on the simulator are durability and size; the device shall be compact enough to be moveable.The resulting simulator fulfils the requirements and enables better repeatability and ability to test extreme cases than experiments on animals do.Uptake of the anaesthetic agent is achieved in a active carbon filter and controlled by regulating the flow. The flow is created by a regenerative blower and controlled using a proportional valve. The uptake can be set by the user or by a simple uptake model modified to recursively handle changes in the concentration of anaesthetic agent.Carbon dioxide is fed into the system from a tank by a mass flow regulator. The supply of carbon dioxide can be set according to a constant flow to simulate a certain production rate, or to achieve a desired concentration of carbon dioxide in the exhaled gas.Heat and moisture is added to the exhaled gas in a chamber partially filled with water. The chamber is heated by self-regulating heating elements and supervised by a combined temperature and humidity sensor.Control and monitoring of the system is implemented in LabView and includes data processing, user interface and communication with sensors, actuators and data acquisition devices.When verifying the functionality of the simulator, tests show the exhaled gas is saturated with moisture and has a temperature sufficiently close to normal body temperature. The deviation of the calculated uptake compared to the measured value is within the requirements for larger flows through the filter. When performing tests with extremely small flows, the performance deteriorates due to limited precision of the flow measurement. Thus, if better performance is desired when simulating small uptakes, improved flow sensing accuracy is recommended.