Cochlear blood flow

The homeostatic mechanisms of the cochlea include those that regulate energy supply, fluid volume and ionic balance, and removal of metabolic waste products. The blood circulation of the inner ear is the major system providing some aspects of these specific functions. The control of the circulation is critical to normal function. However, there is much that needs to be learned about basic pathophysiological questions on inner-ear blood flow and specifically about microcirculation of the inner ear. Does sound influence cochlear blood flow in ways that have important physiological consequences to hearing? Is vascular permeability (and the pathology of permeability) a determinant of ear lymphatic volume or pressure or ionic content? What percentage of sudden hearing loss in the human population is due to vascular insufficiencies? Clearly, the answers to such questions require unique studies of inner-ear circulation. It is not sufficient to generalize the findings from other organ systems to the inner ear because considerable heterogeneity occurs in different vascular beds. For example, in the choroid arterioles of the guinea pig, four different neurotransmitters/neuromodulators (norepinephrine, ATP, acetylcholine, and nitric oxide) are found to be active (Hashitani et al., 1998). In the cochlea, neuropeptides are also likely to be important for vasoregulation (e.g., Carlisle et al., 1990a).