[Experimental studies on the suppression of the stapedius reflex in comparison with EMG-results in idiopathic facial paresis].

The recording of intra-aural muscle reflexes elicited by acoustic stimulation is a routine method in clinical audiology. The most important quantitative examinations of the reflex dynamic, i.e. Metz recruitment and reflex decay in low frequencies, allow the judgement of function of the afferent pathway in the stimulated inner ear and acoustic nerve. Quantitative determinations of the efferent branch were carried out by several authors in a few normal subjects and in several patients with multiple sclerosis or facial palsy. Absolute acoustic impedance - a method yielding wide scattering - was used in order to determine changes in reflex activity in pathological conditions. In the first part of our investigations we tried to find a parameter or reflex dynamic allowing to characterize the functional capacity in the efferent part of the reflex arch in the facial nerve. We examined particularly the steepness of the onset of recorded reflex. Statistical analysis showed an extraordinary stability of this parameter in normal and pathological conditions. Measurements in normal subjects yielded very small intra- and inter-individual variability. In the second part of our experiments we studied normal-hearing patients with unilateral Bells palsy. In the early phase of the lesion we found a significant decrease of the onset steepness in the reflex diagram recorded on the paralyzed side. The greatest reduction of this parameter was seen with a 1,000-Hz stimulus. The time course of the alteration of the onset steepness also seems to have a characteristis pattern. In a further investigation we compared the variations of this reflex parameter with findings in stimultaneously recorded electroneuronograms.