OTOLOGY Hydrostatic fluid pressure in the vestibular organ of the guinea pig Jonas J.-H. Park • Jahn J. Boeven • Stefan Vogel • Steffen Leonhardt • Hero P. Wit • Martin Westhofen Received: 25 August 2011 / Accepted: 6 October 2011 / Published online: 2 November 2011 Ó Springer-Verlag 2011 Abstract Since inner ear hair cells are mechano-electric transducers the control of hydrostatic pressure in the inner ear is crucial. Most studies analyzing dynamics and regu- lation of inner ear hydrostatic pressure performed pressure measurements in the cochlea. The present study is the first one reporting about absolute hydrostatic pressure values in the labyrinth. Hydrostatic pressure of the endolymphatic system was recorded in all three semicircular canals. Mean pressure values were 4.06 cmH 2 O ± 0.61 in the posterior, 3.36 cmH 2 O ± 0.94 in the anterior and 3.85 cmH 2 O ± 1.38 in the lateral semicircular canal. Overall hydrostatic pressure in the vestibular organ was 3.76 cmH 2 O ± 0.36. Endolymphatic hydrostatic pressure in all three semicir- cular canals is the same (p = 0.310). With regard to known endolymphatic pressure values in the cochlea from past studies vestibular pressure values are comparable to cochlear values. Until now it is not known whether the reuniens duct and the Bast’s valve which are the narrowest passages in the endolymphatic system are open or closed. Present data show that most likely the endolymphatic system is a functionally open entity. Keywords Inner ear hydrostatic pressure Á Endolymphatic Á Labyrinth Á Bast’s valve Á Reuniens duct Introduction The balance of the hydrostatic pressure in the inner ear is crucial for its function. Since the labyrinth and the cochlea are mechano-electric transducers, changes of the perilym- patic and endolymphatic hydrostatic pressure lead to alterations of electrophysiological transmission [1]. The inner ear pressure is controlled by sophisticated regulatory mechanisms which are not fully understood. The cochlear aqueduct plays a major role in the inner ear pressure reg- ulation in case of pressure transfer via middle ear and ossicular chain [2]. Transfer of intracranial pressure to the inner ear can be regulated by the cochlear aqueduct [3]. Although the endolymphatic sac function is discussed controversially, it is generally regarded as the determinant factor in endolymphatic fluid volume regulation [4]. Various studies analyzed the hydrostatic fluid pressure in the cochlea by different methods [5–11]. Most authors did not find difference between the perilymphatic and the endolymphatic pressure. Measured values of hydrostatic pressure in the perilymphatic space ranged from 1.2 cmH 2 O to 4.7 cmH 2 O. In the endolymph the pressure was found to be between 1.2 cmH 2 O and 4.1 cmH 2 O, depending on the study performed. Acute pressure changes in the inner ear are compensated to a certain degree [12]. Studies showed that cochlear function is stable to peri- lymphatic pressure changes in the range of -100 to 700 Pa [13], whereas pressure changes in the endolymphatic space J.J.-H. Park and J.J. Boeven have contributed equally to this work. J. J.-H. Park (&) Á J. J. Boeven Á M. Westhofen Department of Otorhinolaryngology and Head and Neck Surgery, RWTH Aachen University, Pauwelsstrasse 30, 52074 Aachen, Germany e-mail: jpark@ukaachen.de S. Vogel Á S. Leonhardt Chair of Medical Information Technology, Helmholtz-Institute, RWTH Aachen University, Pauwelsstrasse 20, 52074 Aachen, Germany H. P. Wit Department of Otorhinolaryngoloy, University Medical Center Groningen, 30 0001, 9700 RB Groningen, The Netherlands 123 Eur Arch Otorhinolaryngol (2012) 269:1755–1758 DOI 10.1007/s00405-011-1813-6