Noninvasive in-ear monitoring of intracranial pressure during microgravity in parabolic flights

Among possible causes of visual impairment or headache experienced by astronauts in microgravity or post-flight and that hamper their performance, elevated intracranial pressure (ICP) has been invoked, but never measured for lack of non-invasive methods. The goal of this work was to test two noninvasive methods of ICP monitoring using in-ear detectors of ICP-dependent auditory responses, acoustic and electric, in acute microgravity afforded by parabolic flights. The devices detecting these responses were hand-held tablets routinely used in otolaryngology for hearing diagnosis, customized for ICP extraction and serviceable by unskilled operators. These methods had been previously validated against invasive ICP measurements in neurosurgery patients. The two methods concurred in their estimation of ICP changes with microgravity, i.e., 11.0 {plus minus} 7.7 mmHg for the acoustic method (n = 7 subjects with valid results out of 30, auditory responses being masked by excessive in-flight noise in 23 subjects), a...