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Factors, both acoustic and non-acoustic, which may influence the Most Comfortable Loudness Level, the Uncomfortable Loudness Level, the Acoustic Reflex Threshold and the Threshold of Overload are reviewed. A direct experimental comparison of these measures was made with respect to their absolute values and the between- and within-subject variances. The Most Comfortable Loudness Level was found to have the greatest within- and between-subject variability. The Uncomfortable Loudness Level, although having high between-subject variability, did not have significantly greater within-subject variability than the Acoustic Reflex Threshold. The significance of these results is discussed.

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The aim of this investigation was to monitor fluctuations in middle ear pressure, to study tympanometric signs of Eustachian tube functioning and to assess the validity of the tympanometric readings. In 20 patients with a low initial middle ear pressure (-150 daPa or lower) and 5 normals, impedance tympanometry was performed every 3 min through 7 h. Median pressure for the patients was -150 daPa (range 100 to -400 daPa) and for the normals 0 daPa (range 50 to -50 daPa). A remarkable pressure increase was seen after changing the body position to the supine. The patients were arranged into three groups according to the lowest middle ear pressure registered. Median pressures for the groups were running at a rather constant level. However, the individual pressure fluctuations in many patients were so great that a single tympanometric reading has to be considered unreliable when selecting patients for insertion of ventilation tubes. Thirteen patients never equalized their negative middle ear pressure, indicating that their Eustachian tube did not open during the test period. In spite of this the pressure did not decrease to lower values, indicating that maintaining a relative constant middle ear pressure is independent of opening of the Eustachian tube.

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