Mechanisms of Respiratory Inhibition Produced by Sudden Aortic Obstruction

¹ From the Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin

External constriction of the descending aorta elicits immediate inhibition of breathing in dogs under Pentothal-chloralose anesthesia both before and after sino-aortic denervation. Impulses initiated by traction of a ligature on the aorta are conducted into the thoracic part of the cord. There is no indication that this mechanism is activated in experiments involving internal occlusion in the innervated animals. Internal occlusion of the descending aorta elicits inhibition of breathing in dogs under morphine sulfate-chloralose anesthesia having all neural pathways intact. The inhibition is related in large part to reflexes from the sino-aortic zones. In the majority of dogs studied the delayed inhibition of breathing following internal occlusion of the descending aorta was greatly reduced but usually not entirely eliminated by sino-aortic denervation. Therefore, some other respiration-inhibiting mechanism is involved. That the respiratory center may be relatively insensitive to changes in blood flow under the conditions of these experiments is indicated by the fact that in individual cases sudden severe changes in blood pressure in sino-aortic denervated animals were not accompanied by changes in respiration.