Betahistine effects on cochlear blood flow: From the laboratory to the clinic

The development of laser Doppler flowmetry techniques has contributed great ly to the study of cochlear blood flow (CBF). In animal models, intravenous betahistine dihydrochloride clearly increased CBF in a dose-dependent mann er. This effect was greater in the cochlear vasculature than in the systemi c vascular bed. The effects of betahistine were blocked by the alpha(2)-ant agonist idazoxan, thus suggesting an interaction between histaminergic and presynaptic adrenergic receptors. This was further supported by studies inv estigating the effects of electrical stimulation on CBF. Local (round windo w membrane) application of betahistine did not affect CBF, but had a non-sp ecific effect on cochlear electrophysiology. This indicates that the recept ors for betahistine vascular effects in the inner ear are most likely locat ed in the modiolar artery. More recently, laser Doppler flowmetry technique s have been applied to human subjects. It has been shown that intratympanic application of adrenaline affects CBF and that this blood flow is under vi gorous sympathetic control. Electrical stimulation has also been used to ob tain measures of dynamic responsiveness in human subjects. This results in an increase in CBF, which is dependent on the intensity of the stimulation. Preliminary evidence indicates that this procedure can provide a standardi zed measure of the dynamic properties of CBF and may provide a means to dif ferentially identify patients with compromised vasculature.