Two degree‐of‐freedom control for constant continuous positive airway pressure of an obstructive sleep apnea treatment system

Abstract

This paper presents a two degree-of-freedom control method for achieving constant continuous positive airway pressure (CPAP) of an obstructive sleep apnea (OSA) treatment system. After constructing a closed-loop DC brushless motor drive together with a blower and an airway module, we develop a pressure control system for achieving CPAP control. A mathematical model of the overall open-loop system is established based on the input-output data and its system parameters are sequentially determined using the recursive least-squares (RLS) method. A two degree-of-freedom (DOF) controller, including a feedforward controller and a feedback proportional-integral controller, is proposed to maintain and follow the desired pressure setpoints. Through experimental results, the proposed control method is shown useful and effective in achieving airway pressure tracking and regulation.

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

“…The mathematical model describes the relation from the input signal of the motor drive to the pressure output. From actual open-loop experimental data shown in Tsai et al (2008), it is confirmed that the steady-state relation between the input voltage of the motor drive (volt) and the output pressure (unit: cmH 2 O) can be indeed modeled by curve-fitting as a quadratic equation, i.e., f (u) = r 0 + r 1 u + r 2 u 2 . Aside from the static relation, the transient behavior of the open-loop system can be experimentally approximated by the linear second-order system model, b 1 z -1 + b 2 z -2 1 + a 1 z -1 + a 2 z -2 , in terms of the z operator.…”

“…In the proposed controller, the feedforward controller is designed to maintain the air pressure inside the mask at a desired setpoint under no human breathing, while the PID feedback controller is synthesized to eliminate or reduce the effect of the human breathing on the air pressure inside the mask. Notice that the transient errors must be controlled to lie within ±2 cmH 2 O according to the U.S. Food and Drug Administration (FDA) criteria for CPAP respirators (American Thoracic Society, 1994;Tsai et al, 2008). Fig.…”

“…In particular, the major cause of the OSA symptom (Behbehani et al, 1995;Yen et al , 1997;Favre et al, 2003;Tsai et al, 2008) is that a patient's airflow ceases because the pharyngeal wall collapses in sleep. It is estimated that about 5% of the general population in the world has a sleep disorder problem (Varady et al, 2002), and 90% of those suffer from the OSA syndrome.…”

“…It was experimentally reported that the desired prescribed pressure near the nasal mask in the CPAP system can be maintained within ±2 cmH 2 O by a two degree-of-freedom (DOF) controller in the presence of the patient's breathing (Tsai et al, 2008). However, this two DOF controller has not been applied to BiPAP machines yet.…”

“…First, a bi-level adaptive pressure controller with fast step tracking performance is constructed based on the two DOF controller studied by Tsai et al (2008); such a controller is equipped with a nonlinear feedforward controller and a gain scheduling PID feedback controller. The merit of the proposed adaptive controller hinges on its strength to make all the transient errors at any time meet the performance criteria provided by the U.S. Food and Drug Administration (FDA) (American Thoracic Society, 1994;Tsai et al, 2008). Second, three methods for breathing period prediction are proposed to automatically provide appropriate inhalation times for the BiPAP respirator.…”