NORMAL VALUES OF HUMAN TYMPANOGRAMS

Acoustic compliance was measured and calculated on tympanograms taken from 160-171 otologically normal human ears with the Middle-ear-function-measuring Apparatus, the test frequency being 300 Hz. The averaged maxium compliance was found to be 1.16 ml at zero ear-canal pressure (C₀), and 1.29 ml at the point where pressure in the ear canal equaled that in the tympanic cavity (C₀). The relative compliance of the tympanometry (amplitude of the tympanogram) was 0.65ml in average, but the individual difference is quite large, varying from the smallest 0.25 ml to the largest 1.61 ml. For the majority (96.1%) of the tested ears, pressure in the tympanic cavity, as shown by the, position of the peak of individual tympanograms, did not exceed 50mm H₂O.
A new term of compliance ratio (CR) is introduced as a measurable parameter to express the gradient of compliance change which is of considerable importance in elinieal tympanogram interpretation. CR is defined as ΔCΔP/C200 where ΔC200 is the over-all amplitude of a tympanogram and ΔCΔP is the compliance shift from the peak to a certain point corresponding to a ΔP pressure change. It is proposed to take 50 and 100 mm H₂O for ΔP in routine compliance ratio measurement and comparison. CR is approximately 0.5 when P is 50 mm H₂O.