PROVOKED FLUX MOTION OF COCHLEAR BLOOD-FLOW MEASURED WITH LASER-DOPPLER FLOWMETRY IN GUINEA-PIG

Although progress has been made in the study of cochlear blood flow (C BF) regulation since laser Doppler flowmetry (LDF) was introduced, coc hlear vasomotion has not been investigated. Therefore, the primary obj ective of this study was to determine if oscillatory fluctuations of C BF could be provoked. Guinea pigs were anesthetized with diazepam (5 m g/kg) and fentanyl (0.32 mg/kg). Blood pressure (BP) was recorded from a carotid artery cannula. The cochlea and pons carebellum were ventra lly exposed; the bilateral CBF and brain blood flow (BBF) or skin bloo d flow (SBF) were monitored by LDF. After administration of phentolami ne (0.25-0.75 mg/kg, i.v.), ipsilateral CBF in 7 of 16 animals showed a 2-5 min episode of oscillation. During artificial hyperventilation, continuous oscillation of CBF was recorded (the flux motion frequency was 3.5 +/- 0.5 cycles per min and its amplitude 25.8 +/- 5.6% from ba seline). The time-dependent flux change (the waveform) was the same th roughout a single cochlea but different between cochleae of the same a nimal. Compared to BBF, CBF vasomotion frequency was lower, and amplit ude larger. SBF exhibited no such motion. Flux motion could be elimina ted by inhalation of pure oxygen or 5% CO2 in oxygen or by the smooth muscle relaxants, papaverine and hydralazine. Phentolamine-induced vas omotion may be due to a hypotensive perfusion pressure, and hyperventi lation-enhanced vasomotion may be caused by changing blood ps concentr ations and by hormonal or neuronal activity. Oxygen and CO2 inhalation slightly increased BP and this change in perfusion pressure was proba bly associated with weakened vasomotion. We conclude that flux motion exists in cochlear microcirculation of guinea pigs and can be provoked by phentolamine and hyperventilation. Oscillation of CBF, as measured by LDF, may be caused by vasomotion of supplying vessels to the cochl ea.