Autoregulation of inner ear blood flow in normal and hydropic guinea pigs

Inner ear and brainstem blood circulation was measured by three different techniques: the laser Doppler (LD), hydrogen clearance (HC) and oxygen tension (PO2) measurements, while systemic blood pressure (BP) was modulated by norepinephrine infusion or removal of whole blood. Results were as follows: (i) The blood flow (BF) change determined by LD correlated well with that measured by HC and PO2 techniques; (ii) BF in the brainstem was maintained constant in the BP range of 35 to 80 mmHg; however, inner ear BF showed a poor autoregulatory function relative to the change of systemic BP; (iii) although the change of BF was similar for cochlea and semicircular canal the amount of PO2 decrease for lowered BP was significantly less in the cochlea than in the canal; (iv) in guinea pigs with unilaterally obliterated endolymphatic sac and duct, the decrease in cochlear BF was larger on the operated side than on the intact side. This suggests that the autoregulatory function for BF is impaired in the hydropic ear.