Design of a simple drive train and control system for an oxygen blend valve for use with premature infants

Abstract

Automating the regulation of the fraction of inspired oxygen (FiO2) in neonatal mechanical ventilation shows great promise of providing better patient outcomes. Historically, controlling the FiO2 valve has required manual adjustment of a control knob, allowing 21 percent-100 percent oxygen to flow to the patient. The current approach requires intense vigilance on the medical staff to ensure that the patients arterial oxygen saturation levels (SpO2) are above the minimum threshold while simultaneously not high enough to risk retrolental fibroplasia (RLF). Retrolental fibroplasia is an abnormal proliferation of fibrous tissue behind the eye lens that can lead to blindness. Retrolental fibroplasia is caused by the administration of excessive oxygen to premature babies. Previous work has included the design and physical construction of an automated FiO2 control valve prototype as well as explored advanced modeling techniques of the prototype and the patient as a complete control system. From this work a second-generation design and six working units were desired with the goal of providing enhanced automated control of the FiO2 valve and the development of a manufacturable design. A design for the mechanical interface was created with the following general requirements: utilizing as much of the existing FiO2 valve design as possible, maintaining the same look and feel to the end user, a desired response time for valve position of one second and allowing for a modular, repeatable manufacturing cycle. After the new mechanical design became functional, open-loop experiments were conducted to provide data for a basic control model. The model was then refined into a closed-loop system with the objective of minimal position error within an acceptable response time based on previous work. This model was then incorporated into the design of the digital controller.