Characteristics of inspiratory inhibition by occlusion of both external carotid and basilar arteries in cats.

Effects of the occlusion of both the external carotid and basilar arteries on the inspiratory activity were studied in anesthetized, vagotomized, paralyzed, and artificially ventilated cats. Integrated phrenic nerve activity was used as an index of the inspiratory activity. Blood pressure in the lingual artery, located downstream from the occluded external carotid arteries, was measured as the arterial pressure of the upper brain stem during occlusion. The basilar artery was occluded at the boundary between the medulla and pons. Occlusions of the external carotid arteries and basilar artery suppressed the phrenic nerve activity to finally disappear within 1 min (phrenic nerve apnea, 45 out of 50 occlusions in 6 cats). The blood pressure in the upper brain stem was 16.6 +/- 5.7 mmHg (mean +/- S.D.) during occlusions. These effects of occlusion on the phrenic nerve activity were also observed during hypercapnia and hypoxia, although they were not so remarkable as those during normocapnia and normoxia. The results indicate that the upper part of the brain stem operates a profound facilitatory mechanism on the medullary inspiratory activity.