Oximetry feedback flow control simulation for oxygen therapy.
OBJECTIVES: For many with Chronic Obstructive Pulmonary Disease (COPD), arterial oxygen saturation while receiving Long-Term Oxygen Therapy (LTOT) falls below an acceptable threshold (SpO(2) < 90%) for extended periods during routine daily activities. Using a closed-loop controller, we have evaluated a simulated method to automatically regulate the oxygen flow-rate in response to the measured oxygen demand. METHODS: The closed-loop control scheme was implemented in a computer simulation on Simulink. Feedback from a pulse oximeter was used to maintain a target SpO(2) of 91% by changing the oxygen flow-rate to the patient. The controller was evaluated using a model to approximate the patient's arterial oxygen saturation response, including hypoxic events from artificial disturbances as well as recorded patient oximetry data. RESULTS: The simulated controller produced improvement in arterial oxygen saturation throughout a wide range of disturbance frequencies. It suppressed disturbances with periods greater than a couple of minutes by more than -10 dB. When evaluated with patient oximetry recordings, the controller on average reduced the time spent with arterial blood saturation below threshold by 76%. Given the same volume of oxygen, the closed-loop controller also produced a 63% improvement compared to fixed flow-rate LTOT. CONCLUSIONS: The simulation findings indicate an optimized matching between oxygen supply and demand, maintaining SpO(2) above threshold to improve therapeutic efficacy compared to standard LTOT.