Autoregulation of cochlear blood flow in guinea pigs

Autoregulation of blood flow in the inner ear following uncontrolled changes in systemic blood pressure (BP), which was induced by the application of pharmacological agents that cause local and/or systemic vascular effects, has been reported in previous studies. In the current study, carotid BP was systematically manipulated without drugs, while the resulting cochlear blood flow (CBF) changes were measured using a laser Doppler flowmeter (LDF). Anesthetized guinea pigs were used, and the probe of a LDF was held against the ventral-posterior portion of the surgically exposed cochlea. A mechanical occluder was placed around the descending aorta or the inferior vena cava. BP could be elevated or lowered over a wide range and was held stable during 2- min occlusions. The mean level (±SD) of regulation (%ΔCBF/%ΔBP) for BP changes less than ±35% of preocclusion baseline was 0.24 ± 0.2 (or 0.18 ± 0.2 if BP is corrected by subtracting central venous pressure). Significant regulation occurred for BP between 20 and 70 mmHg. A demonstration of the cochlear origin of the regulatory response was obtained by 'pharmacological blockade' following topical application of the vasodilator, sodium nitroprusside, to the cochlea. In this condition, CBF changed in nearly direct proportion to BP.