A flexible system for closed-loop ventilator development

The feasibility of using a microcomputer to regulate the delivery of artificial ventilation was investigated experimentally. To carry out this study, a sampled-data proportional, integral, derivative feedback controller was implemented on a commercial microcomputer and interfaced with a digital/analogue model of a prototype ventilator and two-compartment patient. The microcomputer sampled end-tidal CO2 and calculated a new frequency of ventilation from the difference of end-tidal CO2 and a desired set point value. Use of a microcomputer programmable in BASIC allowed easy manipulation of feedback structure. With the proper choice of feedback constants, the microcomputer was able to maintain end-tidal CO2 at a desired set point.