Middle ear assessments

Method

Reference

Ear canal volume at threshold auditory response.

Normal range > 0.2 cm∙s3

The GSI 38 measures combined volume of the ear canal and the middle ear space. An ear canal volume greater than 0.2 cm3 may indicate tympanic membrane perforation due to trauma or abnormal laxity of the tympanic membrane in response to acoustic pressure.

GSI 38

Grason-Stadler 2005-Auto Tymp. Graason-Stadler A division of VIASYS Health Care, 5225. Verona Rd, Building 2, Madison, WI 53711.

Peak middle ear pressure at threshold auditory response

Normal range −150 daPa to + 100 daPa

The GSI 38 measures peak middle ear pressure achieved in response to tympanic membrane change associated with tympanic muscle contraction. This is tested over the range of +200 daPa to −400 daPa.

Low pressures may accompany Eustachian tube dysfunction.

GSI 38

(Grason-Stadler 2005)

Gradient middle ear pressure at threshold auditory response.

Normal range 60 - 150 daPa

Percentage length of the base of the stapes reflex divided by the total duration of the reflex.

(A measure of the strength of the stapes reflex during its maximal period of contraction)

The term “threshold” refers to the first reflex response which typically occurs at a frequency of 500Hz in a decibel range of 90 to 110.

Projected Stapes amplitude

(Alternative measure of stapes contraction strength)

Time-to-off-set of the stapes reflex contraction divided by the base length (a measure of any acoustic-reflex offset, advance or delay).

The GSI 38 measures the middle ear pressure gradient, for which the normal range is 50 to 110 daPa. High gradients are indicative of middle ear effusion.

The GSI 38 traces the stapes reflex contraction to maximum amplitude of 8 millimetres, after which it traces a basal threshold formed for the maximum portion of the reflex. The length of this basal portion divided by the total duration of the reflex contraction was multiplied by 100.

Direct measurement of stapes amplitude at the intersection of projected onset and offset contraction gradients.

Threshold base directly measured and compared with the total duration of the stapes reflex, from initiation to time of offset.

GSI 38

(Grason-Stadler 2005).

GSI 38

(Grason-Stadler 2005).

GSI 38

(Grason-Stadler 2005).

GSI 38

(Grason-Stadler 2005)