[Measurements of the acoustic reflex at variable static pressures (author's transl)].

Acoustic reflex measurements are made on thirty normal and three early stage otosclerotic ears at different static pressures in the ear canal and recorded as reflex-tympanogram at 200 Hz and 660 Hz probe-tone frequency. Acoustic reflexes were elicited contralaterally with a pure-tone stimulus at 2,000 Hz. This stimulus was chosen to avoid technical artifacts. An example of a normal acoustic reflex pattern as a function of variable static pressure is presented (Fig. 1). This record was made at 20 dB above the subjects reflex threshold, using 660 Hz probe-tone frequency. The reflex deflection of susceptance is positive up to pressures of plus or minus 50 mm H2O and then becomes negative. The reflex deflection of conductance is negative in the total range. A stiffened middle-ear system shows negative reflex deflection of both admittance components. The reflex-tympanograms (Fig. 2) show the admittance component curves as a function of variable static pressure with and without eliciting the acoustic reflex in case of a normal ear, using probe-tone frequencies of 220 Hz and 660 Hz at 10 dB and at 20 dB above the subjects reflex threshold. The reflex-tympanogram in case of an early stage otosclerotic ear shows negative reflex deflection of susceptance within the total pressure range indicating pathological stiffness (Fig. 3). The reflex related change of the dynamic properties was stimulated in a mathematical model of the middle-ear (Fig. 4). The measurements could be explained in a mathematical approach.