Neural and humoral factors affecting ventilatory response during exercise.

The principle of feedback control is thought to be fundamental for maintaining homeostasis in biological systems. In the respiratory system, constancy of arterial Pcoz, Poz, and pH is also maintained essentially by means of a feedback control system. For the sake of simplicity, let's assume that the respiratory system is regulated by only one controlled variable, Pa~oz. According to control theory, the basic structure of a feedback control system may be represented by two components, a controller and a controlled system (plant) as shown in Fig. The controller of the respiratory system consists of the medullary respiratory center, central and peripheral chemoreceptors and related sensory and motor nerve systems. The controlled system is the lung gas exchanger in which numerous alveoli, conductive airways, pulmonary capillaries, and respiratory muscles in the chest wall and the diaphragm are involved. The purpose of the respiratory feedback system is to keep the output of the controlled system, i.e. the controlled variable, within a relatively narrow range around the desired value or set point under any conditions.