Developing a device measuring the middle ear reflex in rat ears: A preliminary study

Abstract

Purpose The middle ear muscle (MEM) reflex is the contraction of the stapedius and tensor tympani muscles in the middle ear cavity in response to loud sound, and relies on a healthy population of auditory nerve fibers. Thus, the MEM reflex can be used as a diagnostic test to quantify auditory nerve survival. This study aims to develop a device to measure the MEM reflex in an animal model, with a long-term goal to develop a biomarker for auditory nerve degeneration. Methods A source device was constructed using a hearing aid speaker attached to a long and thin tube to create high impedance. A probe consists of a microphone placed near the tip of the tube and the sound source. Sound pressure that reflects the MEM reflex was measured in the probe ear of anesthetized rats while an elicitor stimulus was presented in an opposite ear. Results The probe to measure the MEM reflex was verified having a constant volume velocity sensitive to changes in sound pressure. Increases in amplitude of sound pressure were apparent when the stimulation signal was presented in the stimulating ear and the amplitude was decreased to baseline when the signal was turned off. After sacrifice of the animal, the reflex was absent. Conclusions Results showed the feasibility of the probe with high source impedance to measure the MEM reflex in animal ears. Absent reflex after animal sacrifice indicates that the MEM reflex measured using this probe was not an artifact or biological noise. Keywords: Middle ear muscle reflex; Impedance; Rat