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 (CBF) regulation since laser Doppler flowmetry (LDF) was introduced, cochlear vasomotion has not been investigated. Therefore, the primary objective of this study was to determine if oscillatory fluctuations of CBF could be provoked. Guinea pigs were anesthetized with diazepam (5 mg/kg) and fentanyl (0.32 mg/kg). Blood pressure (BP) was recorded from a carotid artery cannula. The cochlea and pons carebellum were ventrally exposed; the bilateral CBF and brain blood flow (BBF) or skin blood flow (SBF) were monitored by LDF. After administration of phentolamine (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 baseline). The time-dependent flux change (the waveform) was the same throughout a single cochlea but different between cochleae of the same animal. Compared to BBF, CBF vasomotion frequency was lower, and amplitude larger. SBF exhibited no such motion. Flux motion could be eliminated by inhalation of pure oxygen or 5% CO₂ in oxygen or by the smooth muscle relaxants, papaverine and hydralazine. Phentolamine-induced vasomotion may be due to a hypotensive perfusion pressure, and hyperventilation-enhanced vasomotion may be caused by changing blood gas concentrations and by hormonal, or neuronal activity. Oxygen and CO₂ inhalation slightly increased BP and this change in perfusion pressure was probably 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 cochlea.