Positive feedback in flow controller reduces ventilator imposed work of breathing for critical care patients

A unique control method for critical care ventilation is described that uses positive feedback of patient flow demand measurements balanced by a pressure-regulating loop to provide overall stability. The method establishes a near zero output impedance in the ventilator system such that the output appears as a constant pressure source. The low impedance results in a highly responsive flow delivery system, substantially lowering imposed work of breathing as compared to conventional methods. The control structure offers natural static decoupling of baseline flow and airway pressure. Although the main control objective is to simultaneously regulate airway pressure and exhaled gas flow in the presence of active patient flow demand, the controller can be used to accurately track arbitrary pressure trajectories thus serving as a foundation for other breath types used in assist ventilation. Dynamic coupling between the flow and pressure loops and nonlinearities in flow resistive components present challenges in maintaining stable control and desired performance at all levels of pressure and patient loading. Methods that have been applied thus far to manage these issues are briefly discussed.