Influence of extreme head rotations on brainstem auditory evoked potentials (BAEP)

The influence of extreme head rotations on BAEP was studied in 47 patients who had vertebral artery angiogram. Patients with and without unilateral hypoplasia of the vertebral artery (VA) lumen were identified and all patients were further divided into two groups: with and without hypertension. The subjects underwent a BAEP examination in three head positions: neutral position, extreme right and extreme left rotation. In the subgroup of patients with hypertension and unilateral VA hypoplasia, and following the rotation away from the non-hypoplastic vessel a statistically significant decrease in the PV wave amplitude and prolonged PV wave latency was found. Head maneuvers in subjects with normal blood pressure or in hypertensive patients with symmetrical VA did not cause significant changes in BAEP. These results document the effect of head rotation in subjects with potentially impaired collateral flow. An increase in the PV wave latency and decrease in its amplitude may reflect subtle changes in the brainstem perfusion in hypertensive patients. These changes maybe due to a reduced capacity to compensate for dynamic obstruction of VA following the head rotations.