The Acoustic Impedance Change as a Measure of Stapedius Muscle Activity in Man A Methodological Study with Electromyography

Abstract

The impedance change of the ear in response to sound, widely used in clinical diagnosis, is generally regarded to be caused by contraction of the stapedius muscle. In the present study acoustic impedance change at 800 Hz and EMG of the stapedius muscle were compared in subjects with unilateral ear drum perforation. Ten per cent of the maximum impedance change was reached at a sound level 5–6 dB above the one that gave 10% of the maximum integrated EMG amplitude. Impedance change and integrated EMG were both approximately linear functions of stimulus sound level at least up to 20 dB above reflex threshold. It was concluded that the impedance change gives an adequate measure of the stapedius muscle activity both at threshold and supra-threshold levels. The value of suprathreshold impedance change measurements in clinical diagnosis was pointed out.