An animal model for the analysis of cochlear blood flood disturbance and hearing threshold in vivo

Impairment of cochlear blood flow (CBF) is considered to be important in inner ear pathology. However, direct measurement of CBF is difficult and has not been investigated in combination with hearing function. Six guinea pigs were used to show feasibility of an animal model for the analysis of cochlear microcirculation by intravital microscopy in combination with investigation of the hearing threshold by brainstem response audiometry (ABR). By the application of sodium nitroprusside (SNP), CBF was increased over 30 min. Reproducibility of measurements was shown by retest measurements. Mean baseline velocity of CBF was 109 +/- A 19 mu m/s. Vessel diameters had a mean value of 9.4 +/- A 2.7 mu m. Mean hearing threshold was 19 +/- A 6 dB. In response to SNP, CBF velocity increased significantly to 161 +/- A 26 mu m/s. Mean arterial pressure decreased significantly to 36 +/- A 11 mmHg. After the end of the application, CBF velocity recovered to a minimum of 123 +/- A 17 mu m/s. Within the retest, CBF velocity significantly increased to a maximum of 160 +/- A 31 mu m/s. Second recovery of CBF velocity was 125 +/- A 14 mu m/s. Within the second retest, CBF increased significantly to 157 +/- A 25 mu m/s. ABR thresholds did not change significantly. The increase in blood flow velocity occurred in spite of substantial hypotension as induced by a vasodilator. This may explain the fact that ABR threshold remained unchanged reflecting a maintained blood supply in this part of the brain. This technique can be used to evaluate effects of treatments aimed at cochlear microcirculation in inner ear pathologies.