First, the respiratory systemis dedicated to a highly specific physiologic function, namely, the exchange of O2 and CO2 through themotor act of breathing. This physiologic function is readily distinguishable from extraneous disturbancesarising from behavioral and other functions of the respiratory muscles. Second, the respiratory controlsystem is structurally well organized, with well-defined afferent and efferent neural pathways, peripheralcontrolled processes, and a central controller. The functional and structural specificity of the respiratorysystem — and the diverse neurodynamic behaviors it represents — make it an ideal model system toillustrate the basic principles of physiologic control systems in general.Like any closed-loop system, the behavior of the respiratory control system is defined by the continualinteraction of the controller and the peripheral processes being controlled. The latter include the respiratorymechanical system and the pulmonary gas exchange process. These peripheral processes havebeen extensively studied, and their quantitative relationships have been described in detail in previousreviews. Less well understood is the behavior of the respiratory controller and the way in which it processesafferent inputs. A confounding factor is that the controller may manifest itself in many differentways, depending on the modeling and experimental approaches being taken. Traditionally, the respiratorycontrol system has been modeled as a closed-loop feedback/feedforward regulator whereby homeostasisof arterial blood gas and pH is maintained. Alternatively, the respiratory controller may be viewed as a
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