Adaptive pressure tracking and breathing period prediction for obstructive sleep apnea treatment respirators with bi‐level positive airway pressure

Abstract

This paper presents techniques for adaptive pressure tracking and breathing period prediction in an obstructive sleep apnea (OSA) treatment system by means of bilevel positive airway pressure (BiPAP). In order to achieve bi-level pressure tracking, a closed-loop high-speed DC brushless motor together with a blower and an airway module was constructed by a proportional-integral-derivative (PID) velocity controller, which was then implemented into a low-cost digital signal processor (DSP) on a Microchip. With this controlled closed-loop airway module, a mathematical model of the overall open-loop system was established based on the input-output data and its system parameters were sequentially determined using the recursive least-squares (RLS) approach. An adaptive pressure tracking controller, including a nonlinear feedforward controller and a gain scheduling PID feedback controller, was proposed to follow desired bi-level pressure setpoints. Three breathing prediction methods are presented to estimate the incoming breathing period, including inhalation and exhalation, in order to automatically provide appropriate inhalation time for the BiPAP respirator. Through experimental results, the proposed control system, together with the proposed breathing period prediction methods, is shown effective and useful in achieving satisfactory bi-level airway pressure tracking by following human breathing conditions.