Perceptual contributions to optimization of breathing.

Besides regulating the energetic cost of breathing, optimization of breathing may involve the alleviation of an uncomfortable breathing sensation. In this article, we consider perceptual contributions to the optimization of breathing. Just as the cost function proposed by Poon depends on ventilation and arterial PCO2 so does the sense of dyspnea. Consequently, we examined the relationship between breathing discomfort and Poon's cost function. Based on our model and psychophysical studies, it appears that breathing discomfort, which can integrate chemical and mechanical inputs to the respiratory controller, may not operate simply as an estimate of a cost function. We explain how our reflex control model can dynamically minimize a cost function such as Poon's. Also, we consider the influence of willful adjustments of ventilation on breathing discomfort. From this we infer that ventilatory optimization may emerge from automatic reflexes and behavioral responses that involve excitatory chemical and inhibitory neuromechanical feedbacks.