1995 OPEN FORUM Abstracts
SERVO LUNG SIMULATOR
Jigish D. Trivedi M.S., Jeff Anderson M.E., Mark Hoyt*, Sandy Metcalf, RRT, Pat McEwen, RRT, Thomas D. East Ph.D. Pulmonary and Respiratory Care Divisions, LDS Hospital and The University Of Utah, Salt Lake City, Utah 84143 *MH Custom Design, Salt Lake City, UT 84047
Introduction : Existing lung simulators do not provide accurate measurement of volume and flow, a wide variety of resistance and compliance values, or adequate simulation of spontaneous breathing and triggering events. The purpose of this project was to design, construct and test an accurate and flexible two compartment lung simulator that would provide a realistic simulation of spontaneous breathing and triggering events.
Methods: Our engineering design goals were as follows:
2 compartment lung model including trachea Flow Rate: 0 - 180 1/min
Tidal Volume: 50 - 4000 mlRespiratory Rate: 0 - 150 Breaths/min
Airway Pressure: -50-+150 cm H_2OCompliance: 1-500 ml/cm H_2O
Simulation of Pressure or Flow TriggeringSimulation of Spontaneous Breathing
Resistance: 5-1000 cm H_2O/l/s.Accuracy< 1%
To accomplish these goals we constructed a computer controlled high speed motor which moves a piston (Figure 1) as necessary for the overall system to behave as if it were a two compartment lung with an active chest wall. Pressure is measured using a solid state transducer. Volume and flow are measured by a precision shaft encoder on the motor which gives a resolution of 100 µL/step. The piston is heated to accommodate the use of heated and humidified gas. Volume, flow and pressure data are collected by the computer at 400 Hz and a mathematical model determines how to move the piston using a model reference adaptive controller. The mathematical model includes pressure or flow triggering as well as user specified spontaneous breathing patterns. Data are displayed in real-time graphics and stored for analysis.
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The system was tested by lab verification of the performance specifications. Accuracy was assessed with a 1 L precision super syringe (Vitalograph, Medical Instrumentation, Buckingham, England) and the Bicore monitor (Irvine, CA) during mechanical ventilation.
Results: All performance specifications were met. Figure 2 illustrates system performance for one particular test condition. Lab analysis confirmed volume resolution of 100 µL/step. This resolution provides accuracy of 0.002-0.01% for adults and 0.04-0.2% for pediatrics. There are no commercial flow or volume calibration devices that can verify this level of accuracy. Comparison with the super syringe and the Bicore device yielded differences of 0.75±0.31% and 1.4±1.2% respectively. These differences are most likely due to errors in the syringe and Bicore devices.
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Conclusion : We have successfully created an accurate, precise and flexible lung simulator that provides a realistic simulation of spontaneous breathing and triggering. Acknowledgment: Siemens Life Support Systems, Solna, Sweden