title: Level alterations of the 2f (1)-f (2) distortion product due to hypoxia in the guinea pig depend on the stimulus frequency.
abstract: Increased intracranial pressure (ICP) is known to affect the levels of distortion product otoacoustic emissions (DPOAEs) in a frequency-specific manner. DPOAEs might, therefore, be used for monitoring the ICP non-invasively. Hypoxia can also cause alterations of DPOAE levels, which can be distinguished from ICP-related changes only, when their characteristics, in particular frequency specificity, are known in detail. DPOAEs at f (2) = 2, 4, 8, 12 and 16 kHz and oxygen saturation (SaO(2)) were continuously monitored in nine spontaneously breathing guinea pigs, anaesthetized by i.m. administration of midazolam, medetomidin and fentanyl, during the respiration of a gas mixture of N(2)O and O(2) containing either 30% O(2) or 13% O(2). Fourteen hypoxic intervals in eight animals were included into final data analysis. Characteristic hypoxic level alterations with a level decrease and a remarkable level destabilization during hypoxia, and a pronounced reversible level decrease after reoxygenation were observed at the frequencies of 4, 8 and 16 kHz. At 2 and 12 kHz, the only reproducible effect of hypoxia was an increased fluctuation of the DPOAE level, which was significantly less pronounced compared with the other frequencies (P < 0.05 for 12 vs. 16 and 8 kHz and for 2 vs. 16 kHz). DPOAE level alterations due to hypoxia depend on the frequency in guinea pigs. Studies in human are warranted to improve non-invasive ICP monitoring with DPOAE by the detection of hypoxia-related changes.
authors.affiliation: Department of Otorhinolaryngology, Head and Neck Surgery, Ludwig Maximilians University of Munich Medical Center, Marchioninistr. 15, 81377 München, Germany. bernhard.olzowy@med.uni-muenchen.de
authors.forename: Bernhard
authors.initials: B
authors.lastname: Olzowy
authors.forename: Gregor
authors.initials: G
authors.lastname: von Gleichenstein
authors.forename: Martin
authors.initials: M
authors.lastname: Canis
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Plesnila
authors.forename: Sebastian
authors.initials: S
authors.lastname: Strieth
authors.forename: Christoph
authors.initials: C
authors.lastname: Deppe
authors.forename: Klaus
authors.initials: K
authors.lastname: Mees
mesh_terms: D000818:Animals; D006168:Guinea Pigs; D000860:Hypoxia / Q000503:physiopathology*; D007427:Intracranial Pressure / Q000502:physiology*; D008991:Monitoring, Physiologic; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology*; D012016:Reference Values; D012815:Signal Processing, Computer-Assisted; D013018:Sound Spectrography