A versatile mechanical ventilator (DIGIT) with high flow stability and a programmable inspiratory phase flow pattern

The paper describes the general characteristics of a newly developed nonconstant-flow generator for automatic ventilation of the lungs. It is known that the application of very high pressure to high internal resistance leads to a very stable flow, in that the flow itself is unaffected by external load (patient) variations. The stability of the flow means that the inspiratory process can be controlled by means of the ventilated volume, thus extending DIGIT utilization to high resistance patients. The modulation of the flow is implemented via a digital electromechanical system, which allows the ventilator functions to be accurately programmed. The desired flow waveform is obtained by means of a series of pneumatic valves, the apertures of which are digitally controlled. The design is innovative in that it allows the flow waveform in each of the ten digitalized time steps into which each inspiratory phase is divided to be both programmed and controlled. Other ventilators commercially available and currently in use do not have this functional capability, as they are all designed to model the integral flow of the inspiratory waveform without being able to modify the subunit time steps of a single inspiratory phase. The paper also discusses the results of fundamental tests concerning the performance characteristics of the ventilator.