Novel design of inspiratory flow generation and gas mixing for critical care ventilators suitable for rapid production and mass casualty incidents.

Scarcity of medical resources inspired many teams worldwide to design ventilators utilizing different approaches during the recent COVID-19 pandemic. Although it can be relatively easy to design a simple ventilator in a laboratory, a large scale production of reliable emergency ventilators which meet international standards for critical care ventilators is challenging and time consuming. The aim of this study is to propose a novel and easily manufacturable principle of gas mixing and inspiratory flow generation for mechanical lung ventilators. Two fast ON/OFF valves, one for air and one for oxygen, are used to control the inspiratory flow generation using pulse width modulation. Short gas flow pulses are smoothed by low-pass acoustic filters and do not propagate further into the patient circuit. At the same time, the appropriate pulse width modulation of both ON/OFF valves controls the oxygen fraction in the generated gas mixture. Tests focused on the accuracy of the delivered oxygen fractions and tidal volumes have proved compliance with the international standards for critical care ventilators. The concept of a simple construction using two fast ON/OFF valves may be used for designing mechanical lung ventilators and thus suitable for their rapid production during pandemics.