EOLE: a system for the automatic control of pO2 and pCO2 during artificial ventilation

Abstract

EOLE is an apparatus for the automatic control of the O2 and CO2 concentrations in the inspiratory, alveolar or mean expiratory gases in artificially ventilated patients. It is composed of an artificial commercial ventilator controlled by a microcomputer, itself receiving information from the ventilator and from sensors. To obtain CO2, the expired gases are recycled through a bag. The gas composition in O2 and CO2 is controlled by two mixing valves. One commands the influx of pure oxygen, the other the relative proportion of room air and of expired gases from the bag. At each respiratory cycle the two mixing valves are driven by the microcomputer, which executes a nonlinear feedback control algorithm taking into account O2 and CO2 measurements as well as the reference commands. The precision of O2 and CO2 is about 4% and the settling time after the imposition of a new reference command is of the order of 3 min.