On Holographic-Interferometric Investigations of the Membrana Tympani (Living Man)

Abstract

The form and amplitude of the vibration of the human eardrum until now has been primarily investigated on the isolated human temporal bone and on living experimental animals. The contemporary approved theory that the umbo has the same amplitude as the surrounding parts of the eardrum originates from v. Békésy (1941); Fig.1. This is hardly understandable technically because the umbo represents the main mechanical impedance. Its amplitude therefore should be reduced as compared to the surrounding eardrum. The expected form of vibration should be similar to that of an eardrum with an acute otitis media (with secretion-stowing in the middle-ear); in this case the maximal excursion is in the largest free area, i. e. in the posterior portion. Corresponding modes of vibration have been demonstrated by several holographers on the isolated temporal bone (TONNDORF and KHANNA, 1972; FRITZE, BURIAN and SCHWOMMA, 1976; v.BALLY, 1977); Fig. 2. investigation in vivo is necessary, however, because the preparation of the isolated specimen has shown to influence the hologram. Moisture is an especially important factor: dryness on the one hand and absorption of irrigation-fluid when fraising on the other hand which can cause distention of the specimen.