Design and development of a novel media-separated valve for flow-controlled expiration during mechanical ventilation.

Mechanical ventilation has become a central therapeutic means in modern medicine. However, mechanical ventilation carries the risk of ventilator-induced lung injury. Our group introduced flow-controlled expiration (FLEX) as an additional approach to effective, lung-protective mechanical ventilation. By gradually reducing the pneumatic resistance, FLEX controls expiratory flow toward a user-set constant target, replacing the exponential flow-time profile of a conventional expiration. Primarily developed to demonstrate the physiological concept, the initial FLEX-system prototype did not provide closed-loop flow regulation and full media separation. These considerations motivated the development of a more advanced system that precisely adjusts pneumatic resistance to achieve rapid closed-loop control of the desired expiratory flow rates. We validated our system through multiple tests using physical lung surrogates. We could effectively control the expiratory flow with two ventilation devices. We thereby demonstrated that the system attenuated high initial expiratory peak flow and guided expiratory flow toward user-selected target values in physical respiratory-system models under a range of physiological and non-physiological conditions. Our system features an innovative valve that enables accurate flow regulation, facilitates easy valve replacement, and ensures complete separation of the respiratory gas space from the ambient environment, thereby enhancing safety and reliability. Moreover, the microcontroller implementation creates a self-contained system, making it well-suited for potential clinical applications.