Significance of a notch in the otoacoustic emission stimulus spectrum.
OBJECTIVE
To explain a clinical observation: a notch in the stimulus spectrum during transient evoked otoacoustic emission measurement in ears with secretory otitis media.


METHODS
The effects of tympanic under-pressure were investigated using a pressure chamber. A model of the ear canal was also studied.


RESULTS
Tympanic membrane reflectance increased as a consequence of increased stiffness, causing a notch in the stimulus spectrum. In an adult, the notch could be clearly distinguished at an under-pressure of approximately -185 daPa. The sound frequency of the notch corresponded to a wavelength four times the ear canal length. The ear canal of infants was too short to cause a notch within the displayed frequency range. The notch was demonstrated using both Otodynamics and Madsen equipment.


CONCLUSIONS
A notch in the otoacoustic emission stimulus spectrum can be caused by increased stiffness of the tympanic membrane, raising suspicion of low middle-ear pressure or secretory otitis media. This finding is not applicable to infants.
Department of Clinical Sciences, Lund University, Lund, Sweden. jan.grenner@med.lu.se
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Grenner
D000328:Adult; D000367:Age Factors; D002675:Child, Preschool; D004424:Ear Canal / Q000033:anatomy & histology / Q000502:physiology; D005072:Evoked Potentials, Auditory; D006801:Humans; D008297:Male; D008953:Models, Anatomic; D010034:Otitis Media with Effusion / Q000503:physiopathology*; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology*; D011312:Pressure; D012984:Software; D014432:Tympanic Membrane / Q000503:physiopathology*