A role for neural pathways in exercise hyperpnea

The ventilatory response to exercise induced by stimulation of the peripheral ends of severed sciatic nerves was studied in seven anesthetized dogs. In response to exercise (n = 23) there were increases in expired minute ventilation (delta VE = 4.09 l/min), arterial CO2 partial pressure (delta PaCO2 = 3.06 Torr), and carotid artery temperature (delta Tca = 0.26 degrees C). There was also a concomitant decrease in mean arterial blood pressure (delta MAP = -6.28 Torr). Since the neural pathways from the exercising limbs to the central nervous system had been eliminated by nerve section, the significant increase in PaCO2 during exercise indicates that humoral factors alone cannot produce the normal exercise response, i.e., an isocapnic hyperpnea. Therefore, neural pathways may play a fundamental role in the ventilatory response to exercise in intact animals.