gms | German Medical Science

Introduction: 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 ICP non-invasively. Hypoxia can also cause alterations of DPOAE levels, which can only be distinguished from ICP-related changes if their characteristics, in particular a frequency-specificity, are known in detail.

Methods: DPOAEs at f2 = 2, 4, 8, 12 and 16 kHz and oxygen saturation (SaO₂) were continuously monitored in 9 spontaneously breathing guinea pigs during respiration of a gas mixture of N₂O and O₂ containing either 30% O₂ or 13% O₂.

Results: 14 hypoxic intervals in 8 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 re-oxigenation were observed at the frequencies 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 to the other frequencies (p<0,05 for 12 kHz vs. 16 and 8 kHz and for 2 kHz vs. 16 kHz).