Effects of bilateral vestibular lesions on orthostatic tolerance in awake cats.

Previous experiments in anesthetized or decerebrate cats showed that the vestibular system participates in adjusting blood pressure during postural changes. The present experiments tested the hypothesis that removal of vestibular inputs in awake cats would affect orthostatic tolerance. Before the lesion, blood pressure typically remained within 10 mmHg of baseline values during nose-up-pitch body rotations of up to 60 degrees in amplitude. In contrast, bilateral peripheral vestibular lesions altered the pattern of orthostatic responses in all animals, and blood pressure fluctuated >10 mmHg from baseline values during most 60 degrees nose-up tilts in five of six animals. The deficit in correcting blood pressure was particularly large when the animal also was deprived of visual cues indicating position in space. During this testing condition, either a decrease or increase in blood pressure >10 mmHg in magnitude occurred in >80% of tilts. The deficit in adjusting blood pressure after vestibular lesions persisted for only 1 wk, after which time blood pressure remained stable during tilt. These data show that removal of vestibular inputs alters orthostatic responses and are consistent with the hypothesis that vestibular signals are one of several inputs that are integrated to elicit compensatory changes in blood pressure during movement.