Vestibular evoked blood flow response in the basilar artery

Background and purpose - Monitoring of the basilar artery (BA) is difficult and has been sparsely performed. The aim of this study was to present phys iological data of functional transcranial Doppler sonagraphy (TCD) of the B A during caloric vestibular stimulation in healthy volunteers. Methods - TC D of the BA was performed in 26 healthy volunteers (14 women, 12 men, age 2 5.1+/-3 years) during caloric vestibular stimulation. Vertigo was documente d using electronystagmography (ENG) and a subjective vertigo scale ranging from 0 to 10 points. Simultaneously, capnogpraphy was performed. Results - All subjects experienced vertigo, nausea and oszillopsia during vestibular irrigation. The average subjective vertigo was for a period of 106 s (+/-65 .4); the average subjective estimated degree of vertigo was 6.7 points (+/- 1.5). In all subjects, ENG demonstrated horizontal nystagm to the left non- irrigated side. In 14 subjects the subjective vertigo was rated by the indi viduals as extreme (point score greater than or equal to 7) and in 12 subje cts as low (point score <7). Mean flow velocity (MFV) in the BA increased s ignificantly during vestibular irrigation, being more prominent in the init ial irrigation and vertigo phase (5.8+/-5.9%, P<0.05) than in the second ve rtigo phase (2.2+/-8.8%, P<0.05). The calculated pulsatility index (PI), wh ich indicates the condition of the small resistance vessels, decreased sign ificantly (-4.9+/-8.1%; -4.3+/-8.9%, P<0.05) during both phases of vestibul ar activation. Endtidal pCO(2) did not change significantly (constant 5.4-/-0.4 Vol%), but respiration frequency was significantly increased during v estibular stimulation (12.3+/-3.8 min(-1) to 16.4+/-5.3 min(-1) and 16.3+/- 4.8 min(-1), P<0.05) probably as a vegetative sign of vertigo. The observed MFV- and PI-changes were more prominent, although not quite significant, i n the subgroup of subjects who experienced extreme subjective vertigo than in the subgroup who experienced low subjective vertigo. Conclusion - These observations indicate that MFV increase in the posterior circulation is due to activation of the vestibulocerebellum. In addition, it is possible that the previously elaborated MFV increase in the MCA might contribute to MFV increase in the BA via the posterior communicating artery. The difference i n the 2 subgroups (extreme vertigo vs low vertigo) may reflect the great va riety of anatomical and physiological conditions of the peripheral vestibul ar organ, the brainstem anatomy and the corresponding blood supply. For cli nical purposes this TCD-test may contribute to the investigation of the vas omotor reserve of the posterior circulation, e.g. in patients with vertebro basilar ischemia, bilateral vestibular loss or local neurodegenerative dise ase.