Optotensometry for Measuring the Tube Function – A Feasibility Study on a Middle Ear Model T. Zehlicke1, 2 , T. Just

2

, C. Punke 2 , M. Stamer 3 , J. Müller 3 , R. Wendlandt 4 , H.-W. Pau 2

1

Armed Forces Hospital Hamburg, Department of Otorhinolaryngology, Head and Neck Surgery Department of Otorhinolaryngology, Head and Neck Surgery„ Otto Körner “, University of Rostock 3 Institute of Microsystem Technology, Hamburg University of Technology 4 University of Lübeck, Department of Ortopedic Surgery 2

Background: The amount of pressure in the middle ear depends mainly on the function of the Eustachian tube. Currently there are no continuous recording techniques measuring Eustachian tube function in clinical context and under physiological conditions over extended periods of time (1-4). In this paper we investigate the suitability of an active optic triangulation method on the basis of a projected laser-point-pattern in measuring tympanic membrane movement during pressure variations in a middle ear model.

Material and Methods: For projection we used a green semiconductor laser with an output of 1 mW and a difractive optical element (DOE). As our measured object we used purple latexfoil (KimberleyClark ® ), fixed airtight on the cut-of end of a 2 ml syringe-tube (Fig. 1). The movement of the foils was measured by an active optic triangulation method (Fig. 2). To simulate pathological variations of the tympanic membrane we prepared the latex-foils in specific ways. One foil was perforated and then covered again (simulating tympanic membrane perforation, Fig. 3), another one was partly strengthened by sticking a piece of thick, hard paper to it from the inside (simulating calcification, Fig. 4).

Fig. 3 Perforated and covered membrane, simulating ear drum perforation

Results: The test-setup, as well as the appliance of pressurechanges worked fine and measurement of foil movement in all the modified foil surfaces was possible (Fig. 5, 6). This shows that it is possible to record foilmovement with this system even in tympanic membranes with pathological variations.

Conclusions: In the course of this study we were able to show that it is possible to assess and record foil movement using a system of optic riangulation and to simulate di. erent tympanic membrane pathologies. This could be used both in ENT medicine, as well as in aviation and diving medicine (5-7). Fig. 1: Green semiconductor laser on the left side, purple latexfoil on the right side Fig. 2: The green laser matrix (arrow) is essential for measuring membrane movements

Fig. 4 Piece of thick, hard paper, simulating calci-fication of the eardrum

Fig. 5 Diagram shows movements of the perforated membrane

Fig. 6 Diagram shows movements of the “calcificated” membrane

References: 1 Koch U, Pau HW Tubenfunktionsstörungen. In: Naumann HH, Helms J, Herberhold C et al., Hrsg . OtoRhino-Laryngologie in Klinik und Praxis. Stuttgart: Thieme ; 1994 ; Volume 1 : 564-581 2 Pau HW, Koch U Tympanometrische Untersuchungen an Mittelohrmodellen. Arch Otorhinolaryngol 1978 ; 221 : 261-267 3 Koch U , Middendorf F Direkte kontinuierliche Bestimmung des Mittelohrdruckes. Laryngo-Rhinol-Otol 1979 ; 58 : 424-434 4 Koch U Die Bedeutung der Tubenmanometrie zur Beurteilung der Tubenfunktion. Arch Otorhinolaryngol 1983 ; 237 : 263-271 5 Zehlicke T, Pau HW, Schmidt W et al. Die Tensometrie – eine neue Technik zur Begutachtung der Tubenfunktion bei Tauchern und Piloten. Biomedizinische Technik 2006 ; 51 : 345-346 6 Di Martino E, Thaden R, Krombach GA et al. Funktionsuntersuchungen der Tuba Eustachii Aktueller Stand. HNO 2004 ; 52: 1029-1040 7 Klingmann C, Praetorius M, Böhm F, Tetzlaff K, Plinkert PK Fitness to dive in the otorhinolaryngological field. HNO 2008 ; 56 : 509-518