Distortion Product Otoacoustic Emissions and Intracranial Pressure During CSF Infusion Testing.

BACKGROUND A noninvasive method to monitor changes in intracranial pressure (ICP) is required for astronauts on long-duration spaceflight who are at risk of developing the Visual Impairment/Intracranial Pressure syndrome that has some, but not all of the features of idiopathic intracranial hypertension. We assessed the validity of distortion product otoacoustic emissions (DPOAEs) to detect changes in ICP. METHODS Subjects were eight patients undergoing medically necessary diagnostic cerebrospinal fluid (CSF) infusion testing for hydrocephalus. DPOAE measurements were obtained with an FDA-approved system at baseline and six controlled ICP levels in ∼3 mmHg increments in random order, with a range from 10.8 ± 2.9 mmHg (SD) at baseline to 32.3 ± 4.1 mmHg (SD) at level 6. RESULTS For f2 frequencies between 800 and 1700 Hz, when ICP was ≥ 12 mmHg above baseline ICP, DPOAE angles increased significantly and DPOAE magnitudes decreased significantly, but less robustly. DISCUSSION Significant changes in DPOAE angle and magnitude are seen when ICP is ≥ 12 mmHg above a subject's supine baseline ICP during CSF infusion testing. These results suggest that the changes in DPOAE angle and magnitude seen with change in ICP are physiologically based, and suggest that it should be possible to detect pathological ICP elevation using DPOAE measurements. To use DPOAE for noninvasive estimation of ICP during spaceflight will require baseline measurements in the head-up, supine, and head-down positions to obtain baseline DPOAE values at different ICP ranges. Williams MA, Malm J, Eklund A, Horton NJ, Voss SE. Distortion product otoacoustic emissions and intracranial pressure during CSF infusion testing. Aerosp Med Hum Perform. 2016; 87(10):844-851.