Cochlear blood flow during stepwise bleeding and CO2 inhalation in the anaesthetized dog and cat

Normal blood flow values, autoregulatory tendency and CO2 sensitivity of the cochlear blood vessels were studied in acute experiments in anesthetized, artificially ventilated dogs and cats. Cochlear blood flow was measured with the hydrogen-gas clearance technique using 100 mu platinum electrodes implanted into the perilymphatic space. Normal mean cochlear blood flow at normal systemic blood pressure and arterial pH values was found to be 30 +/- 7 ml . 100 g-1 . min-1 in the dog, and 16 +/- 5 ml . 100 g-1 . min-1 in the cat. There was no evidence of the existence of an autoregulatory mechanism of cochlear blood flow during stepwise bleeding in the dog. Blood flow seemed to follow passively the changes of arterial pressure. Cochlear blood flow increased by 79% on 5% CO2 inhalation in the cat, as a result of decreased vascular resistance. The relationship between arterial pCO2 values and cochlear blood flow proved to be exponential.