[Inverted acoustic reflex: an analysis of its morphological characteristics in different physiological and pathological situations].

INTRODUCTION AND OBJECTIVES: Inverted acoustic reflex (IAR) or inverted acoustic effect is the name given to the positive deflexion observed during the carrying out of an admittancemetry when the ear is subjected to a high intensity sound, rather than the typical negative deflexion due to the contraction of the middle ear musculature. The objective of the paper is to analyze the morphology of the IAR by relating it to the situations (physiological or pathological) in which this effect appears with the aim of establishing a pathogenic hypothesis.

METHODS: We study the admittance traces obtained in 50 patients on stimulating the ear with high sound intensities (between 100 and 110 dBs HL) in different situations (ageing, death, otosclerosis, facial palsy, perception hypoacusia and normoacusia). We analyse the morphologies of the resulting traces as well as the on-set and off-set latencies of the reflexes.

RESULTS: The morphology and latency parameters are similar in all cases in which IAR appears, regardless of the physical conditions of the ear but always with the prior condition of the absence of any contraction of the stapes bone muscle. The inverted acoustic effect does not disappear after deep muscular relaxation induced by anaesthesia and is present in corpses at a time when neural activity can no longer take place.

CONCLUSIONS: Although some of the characteristics of IAR cannot be explained by purely mechanical hypotheses, the appearance of this effect in a corpse and its non-disappearance with muscular relaxation means that we consider its origin to be a purely mechanical effect not mediated by any muscular reflex contraction in the human middle ear.