Effect of hypercapnic blood injection into the vertebral artery on the phrenic nerve activity in cats.

Hypercapnic blood was injected into the vertebral artery in anesthetized and paralyzed cats. The stimulating effect on the phrenic nerve activity was dependent on the injection rate, duration, and PCO2 level of the injected blood. The time delay from the start of injection to the onset of increase in phrenic nerve activity was inversely proportional to both the injection rate and the PCO2 of injected blood.