Ventilatory instability during sleep: New insights from the computational model

We developed a computational model of the human respiratory system and its chemoreflex control during sleep [1] [2]. Our model, which is an extension of the model of Grodins et al. [3], combines an accurate description of a plant with a novel controller design. The controller consists of two feedback loops (central and peripheral) each with its own delay and gain. The overall minute ventilation is a sum of central and peripheral components. The model was employed to develope a new graphical method for stability analysis of the respiratory control system similar in concept to the phase plane [2] [4]. The relative chemosensitivities of the peripheral and central loops serve as the plane's coordinates. A region of stability exists with the normal operating point for the system lying well inside its boundaries. Changes to the sensitivities of either loop, caused by known pathologies, displace the operating point toward the border of the stability region. Furthermore, the shape and area of the stability region is significantly influenced by changes in the cerebral blood flow.