Closed-loop control of a continuous positive airway pressure device

During continuous positive airway pressure (CPAP) therapy, the airway pressure (Paw) should be maintained almost constant during the entire respiratory cycle to minimize the patient work of breathing (WOB). We developed a CPAP setup using a closed-loop control acting on a miniature proportional valve that regulates the Paw established by the CPAP device. Spontaneous breathing was simulated by mechanically ventilating one of the two compartments of a lung simulator that passively displaced the other compartment connected to the CPAP setup. Paw dropped only 0.23 hPa below the 5 hPa and 10 hPa CPAP levels used, at a peak inspiratory flow of approximately 0.59 1/s. In the worst case, Paw was 2.4 hPa above 10 hPa CPAP level during about 0.135 s when peak expiratory flow achieved 1.1 1/s, followed by a 0.33 hPa undershoot. WOB, visualized by plotted pressure x volume curves, was smaller using the closed-loop control as compared to the open-loop CPAP device. The closed-loop control utilized in the present CPAP setup seems to be able to minimize the pressure variation and thus reduce the WOB during the use of CPAP therapy.