Regulation of Respiration During Muscular Activity

Abstract

The mechanism of exercise hyperpnea was investigated employing a cross-circulation technique in which the head of a dog (humoral dog) was perfused exclusively by blood from another dog (neural dog) by way of the carotid arteries and the external jugular veins. The lower extremities of both dogs were induced to exercise separately by stimulating with 60-cycle alternating current, which is modulated sinusoidally. Forty-four experiments were performed on nine pairs of such preparations. The ventilation of the neural dog (exercising) first overshot, then attained a steady state, but the ventilation of the humoral dog overshot to a much higher level when its hind legs were exercised. During the steady state the ventilation of the neural dog (when it was exercising) increased in direct proportion to oxygen consumption. The slope of the regression line expressing the increment in ventilation as a function of oxygen consumption in the neural dog is 0.0298, which is not statistically different from that established for intact dogs during induced exercise or from that in normal dogs during voluntary exercise. The humoral dog whose head was perfused by arterial blood from the exercising neural dog showed no change in ventilation. Therefore, it is concluded that there is no humoral agent produced in the arterial blood of a dog subjected to this type of exercise. The normalcy of the respiratory apparatus in the humoral dog after the establishment of the cross circulation was tested by CO₂ inhalation and lobeline administration and it was found to be adequate.