Acoustic Impedance Bridge Measurements with the Neonate

This paper describes measurements carried out using a Madsen ZO70 acoustic impedance bridge on a population of 98 neonates ranging in age from 5 to 218 hours. A viable technique was developed which enabled tympanograms to be obtained from all the subjects. The tympanograms were seen to fall into two categories, single and double notch. Evidence was found that the double notch is produced by a flaccid tympanic membrane and that maturation to the single notch form takes place. A clear stapedius reflex was obtained from 16% of all the ears tested when contralateral stimulation was applied with a Barany noise box. Earlier maturation was found to occur in bottle fed neonates than in those that were being breast fed. A valsalva test performed by pinching the nose of the neonate during exhalation produced a positive result in 40 cases. Normative data are presented for the acoustic impedance of the middle ear and a comparison is made between this information obtained with the acoustic impedance bridge and sounds relayed to an observer from a microphone placed in the meatus of the subjects.