Model of respiratory sensation and wilful control of ventilation.

A mathematical model has been developed that includes sensations of breathlessness and a dynamic CO2 respiratory controller. Breathing sensations, which are represented as a discomfort index, are assumed to depend on arterial PCO2 level, automatic and wilful motor commands and mechanoreceptor feedback. Wilful control is assumed to arise from cortical centres of the brain and is independent of the reflex control system. The bulbopontine respiratory controller produces the automatic motor command, which is determined by chemical and mechanical feedback. Simulations demonstrate how the controller output and breathing sensations change when wilful motor commands disturb spontaneous breathing. Simulations include isocapnic hyper- and hypoventilation and deliberate hypoventilation during CO2 rebreathing. Simulations are compared with experimental data from human subjects. Simulations predict that the discomfort index intensifies when ventilation is either voluntarily raised or lowered from the optimal level; and discomfort is greater when ventilation is lowered than when it is raised at a given level of PCO2. The simulated results agree with those obtained experimentally. The simulations suggest that respiratory drive integration may depend not only on the direct effects of chemical and mechanical feedback, but also on the perceptual consequences of these stimuli.