Control of respiration in exercising dog: Interaction of chemical and physical humoral stimuli

The ventilatory response to exercise was studied on awake dogs trained to run on a treadmill. The exercise were performed at a grade and speed inducing an increase in the energy metabolic level up to 7 times the resting value. The roles of nervous and humoral stimuli in ventilatory control were analyzed by measuring ventilatory flow rate, tidal volume and respiratory frequency during exercise in three gaseous environments (air, hypoxia and hypercapnia) before and after carotid chemodenervation. At the start of exercise, the marked early rapid change of ventilation was unaffected by the gaseous environment. The terminal fall of ventilation was smaller than the early increase and its magnitude was decreased by hypoxia and hypercapnia. The 02 stimulus was lessened by exercise. For given levels of energy metabolism and of rectal temperature, hypoxia and hypercapnia altered the ventilatory pattern: the ventilatory frequency was decreased while the ventilatory flow rate and tidal volume were increased, inducing then an increase in alveolar ventilation. Hyperpnea related to hyperthermia was unaffected by the gaseous environment. Sinocarotid chemodenervation altered the exercise ventilatory pattern: for a given energy metabolism level, tidal volume was decreased and respiratory frequency increased. The transient rapid changes of ventilation of both the beginning and the end of exercise were altered.