Control of breathing in the exercising dog

Abstract

The ventilatory response to exercise was studied on awake dogs trained to run on a treadmill. Various combinations of speed and grade produced metabolic increases up to 6.5 times the resting value. Ventilatory flow, tidal volume and respiratory frequency were measured cycle by cycle for the purpose of analyzing the roles of nervous and humoral stimuli in ventilatory control. In light work, neurogenic stimuli play an important role in ventilatory control and are responsible for almost all the increase in ventilation. Some minutes after the beginning of exercise a delayed humoral stimulation comes into play. Thermal polypnea develops progressively; its intensity depends on the metabolic level. The respiratory centers are organised in such a way that the dog provides for both its metabolic and thermolytic needs. Thus, in light exercise performed at 19 °C ambiant temperature, Pa O 2 , Pa CO 2 and arterial pH are not modified by thermal panting. Thermal polypnea induces no relative alveolar hyperventilation unless the work load is high or the environment does not allow an important heat loss.