title: Frontal cortical oxygenation changes during gravity-induced loss of consciousness in humans: a near-infrared spatially resolved spectroscopic study.
abstract: Gravity (G)-induced loss of consciousness (G-LOC), which is presumably caused by a reduction of cerebral blood flow resulting in a decreased oxygen supply to the brain, is a major threat to pilots of high-performance fighter aircraft. The application of cerebral near-infrared spectroscopy (NIRS) to monitor gravity-induced cerebral oxygenation debt has generated concern over potential sources of extracranial contamination. The recently developed NIR spatially resolved spectroscopy (SRS-NIRS) has been confirmed to provide frontal cortical tissue hemoglobin saturation [tissue oxygenation index (TOI)]. In this study, we monitored the TOI and the standard NIRS measured chromophore concentration changes of oxygenated hemoglobin and deoxygenated hemoglobin in 141 healthy male pilots during various levels of +G(z) (head-to-foot inertial forces) exposure to identify the differences between subjects who lose consciousness and those who do not during high +G(z) exposure. Subjects were exposed to seven centrifuge profiles, with +G(z) levels from 4 to 8 G(z) and an onset rate from 0.1 to 6.0 G(z)/s. The SRS-NIRS revealed an approximately 15% decrease in the TOI in G-LOC. The present study also demonstrated the TOI to be a useful variable to evaluate the effect of the anti-G protection system. However, there was no significant difference found between conditions with and without G-LOC in subjects with terminated G exposure. Further studies that elucidate the mechanism(s) behind the wide variety of individual differences may be needed for a method of G-LOC prediction to be effectively realized.
authors.affiliation: Department of Hygiene and Preventitive Medicine, Showa University School of Medicine, Shinagawa-ku, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Kurihara
authors.forename: Azusa
authors.initials: A
authors.lastname: Kikukawa
authors.forename: Asao
authors.initials: A
authors.lastname: Kobayashi
authors.forename: Toshio
authors.initials: T
authors.lastname: Nakadate
mesh_terms: D000328:Adult; D000337:Aerospace Medicine; D001359:Aviation; D005625:Frontal Lobe / Q000378:metabolism*; D006801:Humans; D018471:Hypergravity / Q000009:adverse effects*; D008297:Male; D016272:Occupational Health; D010100:Oxygen / Q000378:metabolism*; D010108:Oxyhemoglobins / Q000378:metabolism; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D014474:Unconsciousness / Q000209:etiology* / Q000378:metabolism
chemical_list: D010108:Oxyhemoglobins; D010100:Oxygen