Pulmonary arterial distension and activity in phrenic nerve of anesthetized dogs

In chloralose-anesthetized dogs a constant-flow, right atrium-to-left pulmonary artery, right-heart bypass was created. The right lung root was completely occluded and an isolated pouch of the main pulmonary arteries was perfused with venous blood at controlled nonpulsatile pressures between 10 and 90 Torr. An increase in pulmonary arterial pouch pressure caused an increase in systemic arterial pressure and in respiratory drive. In animals with afferent nerves intact, the increase in respiratory drive was indicated by an increase in the amplitude of the integrated phrenic electroneurogram. In animals with the left vagus nerve cut immediately above the left lung root, the increase in respiratory drive was evident by a shortening of the time of expiration. All responses were abolished by bilateral section of the cervical vagosympathetic trunks. It is concluded that in the preparation described pulmonary arterial distension causes a reflex increase in systemic vascular resistance and in respiratory drive, the afferent path of the reflex being in the vagus nerves.