International Scholarly Research Notices / 2011 / Article / Fig 1

Research Article

Diagnostic Potential of Distortion Product Otoacoustic Emissions in Noninvasive Assessment of Elevated Intracranial Pressure: Different Patterns of DPOAE Alterations in the Guinea Pig

Figure 1

DPOAE levels (left vertical axis) and ICP (right vertical axis) plotted versus time for one pressure step in a single animal. The shaded areas mark data sets with stable ICP included into the final data analysis. The horizontal dotted lines mark the mean DPOAE level before ICP elevation (meanpreICP), under elevated ICP (meanICP), and after ICP normalization (meanpostICP). For the second pattern, meanpostICP was calculated after the supposedly postischemic alterations of the DPOAE levels had abated. (a) First pattern of DPOAE level changes, attributed to altered middle ear sound transmission. Note the prompt level decrease with ICP elevation, the stable DPOAE levels during constant ICP, and the instant recovery of the DPOAE levels after ICP normalization ( 𝑓 2 = 2 kHz). (b) Second pattern of DPOAE level changes, that might be attributed to reduced CoBF. Note the more pronounced level decay and the instability thereafter. After ICP normalization, the DPOAE levels start to recover but then decrease again sharply before they slowly recover to pre-ICP values ( 𝑓 2 = 12 kHz).

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