Measuring Cochlear Blood Flow by Laser Doppler Spectroscopy

Cochlear blood flow (CBF) was studied with a commercially available laser Doppler system in 20 guinea pigs. The cochlea was exposed to permit placement of the laser Doppler probe over the intact lateral wall of the basal turn. Ketamine and xylazine were used for anesthesia, and blood pressure was monitored from the femoral artery. In some cases, skin blood flow was monitored with a second laser Doppler system, and cardiac output was monitored with an ultrasonic Doppler system placed over the right brachiocephalic artery. We found that the laser Doppler signal is composed primarily of blood flow supplied by the internal auditory artery. Local pressure on the contents of the internal auditory canal after occipital craniotomy was found to reduce CBF to 15% of its original value in a reversible fashion. There was no change in CBF after bilateral occlusion of the common carotid arteries. There appears to be a mechanism governing CBF that stabilizes its value in the face of changes in blood pressure and cardiac output. This is similar to the vascular behavior of the central nervous system. Through the use of positive airway pressure and blood removal at different rates, cardiac output could be depressed to varying degrees. The magnitude of decrease in CBF was clearly related to the rate at which cardiac output and blood pressure dropped. This was confirmed when intravenous phenylephrine was given in sequential and increasing doses. CBF increased as blood viscosity decreased, as expected according to the vascular behavior of the central nervous system.(ABSTRACT TRUNCATED AT 250 WORDS)