Effects of ketamine on the adaptive responses of second-order vestibular neurons of the cat

Local vestibular blood flow and systemic vascular responses to natural vestibular stimulation in the Mongolian gerbil

HYPOTHESIS

Natural stimulation of the vestibular end organs will produce alterations in the local vestibular microvascular blood flow.

BACKGROUND

The vestibular and cardiovascular systems require a coordinated interaction to maintain organ perfusion during rapid positional and postural changes. However, the detailed relationship of these systems is not well understood. There have been no previous descriptions of local vestibular blood flow (VBF) during natural stimulation (NS) conditions.

METHODS

In vivo VBF and systemic blood pressure (BP) in the Mongolian gerbil during natural stimulation. Using laser Doppler flowmetry, the authors obtained continuous measures of local VBF in both anesthetized and alert gerbils during sinusoidal rotational stimuli. Simultaneous recordings of systemic BP were collected from the contralateral common carotid artery.

RESULTS

The anesthetized gerbils showed stable VBF and BP during all vestibular stimuli. By contrast, alert subjects demonstrated a significant response to natural stimulation. The VBF increased 28% over baseline, and systemic BP increased 8% during a 45-second, 0.133-Hz sinusoid. Decreases in BP of 8% and 5%, respectively, were seen with a 0.10 and 0.20 Hz, 360-second stimulus. A corresponding determination of VBF during the extended stimulus conditions was not technically possible.

CONCLUSIONS

To the authors' knowledge, these are the first in vivo descriptions of vestibular blood flow during natural stimulation. In the alert animals, VBF increased in response to NS. This increase in flow does not appear to be directly dependent on systemic blood pressure changes and indicates that the vestibular microvasculature is closely regulated.

Unique case of pulsatile tinnitus

Tinnitus is a common symptom encountered by otolaryngologists. Pulsatile tinnitus is rare and can present a diagnostic challenge. Establishing a diagnosis is important, because pulsatile tinnitus may indicate serious intracranial or extracranial disease. A unique case of pulsatile tinnitus caused by cervical artery dissection is presented, along with the differential diagnosis and treatment.