Tianying Ren

A reversible ischemia model in gerbil cochlea

A completely reversible cochlear-ischemia animal model was developed, and an initial study of ischemia/reperfusion-induced cochlear function change is presented. The bulla of the anesthetized gerbil was opened through a ventral approach and the anterior inferior cerebellar artery and its branches were exposed. Cochlear blood flow (CBF) from the basal turn of the cochlea was monitored with a laser Doppler flowmeter. An electrically isolated microclamp was used to occlude the labyrinthine artery (LA). During LA clamping, the cubic distortion product (DP) was continuously recorded. The LA was repeatedly clamped for different durations in all animals, and CBF consistently showed full recovery after clamp release. No obvious change in vessel diameter or flow pattern was observed under a stereomicroscope. Mean blood pressure did not show significant change during clamping. Immediately upon LA clamping, CBF decreased rapidly nearly to zero. After clamp release, CBF demonstrated an immediate rapid increase, followed by a secondary gradual recovery to baseline. CBF recovery patterns were clamp duration-related. Within a few seconds of occlusion, DP decreased and reached a minimum of approximately 24% of the initial level in less that 30 s. Following reperfusion of the cochlea, DP gradually increased, decreased again, then slowly recovered. Time delay between CBF reperfusion and the first increase of DP was proportional to clamping duration, and the increased amplitudes demonstrated a negative relationship to clamp duration. We assume that the first decrease in DP during clamping was caused by ischemia in the cochlea; the second decrease, during the cochlear reperfusion, could be a form of reperfusion-induced change in cochlear function. This ischemia/reperfusion model in gerbil cochlea demonstrates excellent repeatability and reversibility. Since DP and other measurements can be used to dynamically monitor cochlear or hair cell functions, this model is useful in studies of auditory physiology and pathophysiology.

Method for evaluating inner ear hearing loss

A method for evaluating the electromotility of hair cells within the cochlea of a mammalian ear by providing an electrode in proximate relation with the round window and applying electricity therethrough in order to electrically excite hair cells within the cochlea to produce electrically-evoked otoacoustic emissions therefrom. The electrically-evoked otoacoustic emissions further excite the internal structure of the cochlea which produces vibrations at the oval window that act through the bones of the middle ear to drive the tympanic membrane, producing corresponding acoustic sounds in the ear canal. The resulting acoustic sounds in the ear canal are subsequently detected with a microphone where they are later measured and characterized via readily available signal processing techniques. A hearing aid device is also provided by this invention utilizing the features of the before mentioned analysis technique wherein a traditional hearing aid device acoustically captures a sound adjacent the outer ear and converts it to an electrical signal which is fed to the electrode in order to excite the hair cells within the cochlea and produce electrically-evoked pressure waves therein. The resulting electrically-evoked pressure waves subsequently excite the cochlea and produce perceived hearing in the brain of the test subject through the normal hearing processes of hair cells and conducting neurons.

Electrically evoked cubic distortion product otoacoustic emissions from gerbil cochlea

It has been demonstrated that electrical stimulation of the cochlear partition results in basilar membrane vibration and otoacoustic emissions. Electromotility of stimulated outer hair cells (OHCs) elicits the electrically evoked otoacoustic emissions (EEOAEs). Although electrically evoked upper and lower sideband distortion products (DPs) have been reported, electrically evoked cubic DP has not been investigated. Since the acoustically evoked cubic DP is the most commonly used otoacoustic measure of cochlear nonlinearity, this study tested whether electrical stimuli evoke a cubic DP otoacoustic emission. An electrical current containing the frequency component f1 and f2 (f1 < f2) was delivered to the round window niche of the gerbil, and electrically induced sound pressure change in the external ear canal was measured with a microphone. It was found that, in addition to f1 and f2 EEOAEs, cubic DP (2f1-f2) and other emissions at 3f1-2f2, 2f2-f1 and f2-f1 frequencies are electrically evoked. The electrically evoked cubic DP growth is similar to that of an acoustically evoked cubic DP. An electrical stimulus at f1 or f2 and an acoustic stimulus at f2 or f1 produce an identical cubic DP to that evoked by two electrical stimuli and/or two acoustic stimuli at f1 and f2 frequencies. An acoustic suppressor at a frequency near f2 can completely suppress an electrically evoked cubic DP emission. These data demonstrate that DPs can be provoked by a complex two frequency electrical current delivered to the round window niche. These stimuli elicit mechanical vibrations, from stimulated OHCs near the round window, which propagate apically toward their characteristic frequency places on the basilar membrane, and produce combination DPs. Electrically evoked cubic DPs appear to be produced by the same nonlinear mechanism that generates acoustically evoked DPs.

Cochlear blood flow measured by averaged laser Doppler flowmetry (ALDF).

This report describes a new approach to estimate the hydromechanical properties of a vascular system. Averaged laser Doppler flowmetry (ALDF) was developed by averaging the flux signal of a laser Doppler flowmeter (LDF) synchronized to the heart cycle. The usefulness of this method was verified by manipulation of the cochlear microvasculature. Twelve pigmented guinea pigs under pentobarbital/fentanyl anesthesia were used. The cochlea was surgically exposed and the LDF probe placed on the bony surface of the first turn to monitor cochlear blood flow (CBF). The LDF flux signal (0.2 s time constant) was sampled by an A/D board at 2 kHz for 255 ms and averaged with synchronization to the heart beat. The mean blood flow, peak to peak amplitude, and time (phase) delay of pulsatile flow were measured from the averaged signal. According to a transmission line model of the vascular system, under a given perfusion pressure, mean flow reflects resistance while amplitude and time delay of the pulsatile flow are related to the reactance component of the impedance of the vascular system. During the formation of photochemically-induced thrombosis in the cochlear microvasculature, there was a dramatic mean flux decrease (90.1 +/- 3.4% from baseline (BL), N = 6). Additionally, a time-dependent decrease in amplitude and time delay of pulsatile flow were indicated by ALDF. These results suggest a large increase in vascular resistance and significant decrease in compliance.(ABSTRACT TRUNCATED AT 250 WORDS)