Effects of bilateral vestibular lesions on orthostatic tolerance in awake cats

Previous experiments in anesthetized or decerebrate cats showed that the ve stibular system participates in adjusting blood pressure during postural ch anges. The present experiments tested the hypothesis that removal of vestib ular inputs in awake cats would affect orthostatic tolerance. Before the le sion, blood pressure typically remained within 10 mmHg of baseline values d uring nose-up-pitch body rotations of up to 60 degrees in amplitude. In con trast, bilateral peripheral vestibular lesions altered the pattern of ortho static responses in all animals, and blood pressure fluctuated >10 mmHg fro m baseline values during most 60 degrees nose-up tilts in five of six anima ls. The deficit in correcting blood pressure was particularly large when th e animal also was deprived of visual cues indicating position in space. Dur ing 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 whic h time blood pressure remained stable during tilt. These data show that rem oval of vestibular inputs alters orthostatic responses and are consistent w ith the hypothesis that vestibular signals are one of several inputs that a re integrated to elicit compensatory changes in blood pressure during movem ent.