White Matter Integrity in High-Altitude Pilots Exposed to Hypobaria.
BACKGROUND
Nonhypoxic hypobaric (low atmospheric pressure) occupational exposure, such as experienced by U.S. Air Force U-2 pilots and safety personnel operating inside altitude chambers, is associated with increased subcortical white matter hyperintensity (WMH) burden. The pathophysiological mechanisms underlying this discrete WMH change remain unknown. The objectives of this study were to demonstrate that occupational exposure to nonhypoxic hypobaria is associated with altered white matter integrity as quantified by fractional anisotropy (FA) measured using diffusion tensor imaging and relate these findings to WMH burden and neurocognitive ability.


METHODS
There were 102 U-2 pilots and 114 age- and gender-controlled, health-matched controls who underwent magnetic resonance imaging. All pilots performed neurocognitive assessment. Whole-brain and tract-wise average FA values were compared between pilots and controls, followed by comparison within pilots separated into high and low WMH burden groups. Neurocognitive measurements were used to help interpret group difference in FA values.


RESULTS
Pilots had significantly lower average FA values than controls (0.489/0.500, respectively). Regionally, pilots had higher FA values in the fronto-occipital tract where FA values positively correlated with visual-spatial performance scores (0.603/0.586, respectively). There was a trend for high burden pilots to have lower FA values than low burden pilots.


CONCLUSIONS
Nonhypoxic hypobaric exposure is associated with significantly lower average FA in young, healthy U-2 pilots. This suggests that recurrent hypobaric exposure causes diffuse axonal injury in addition to focal white matter changes.McGuire SA, Boone GRE, Sherman PM, Tate DF, Wood JD, Patel B, Eskandar G, Wijtenburg SA, Rowland LM, Clarke GD, Grogan PM, Sladky JH, Kochunov PV. White matter integrity in high-altitude pilots exposed to hypobaria. Aerosp Med Hum Perform. 2016; 87(12):983-988.
Department of Neurology, 59th Medical Wing, Joint Base San Antonio-Lackland, TX, USA.
Stephen A
SA
McGuire
Goldie R E
GR
Boone
Paul M
PM
Sherman
David F
DF
Tate
Joe D
JD
Wood
Beenish
B
Patel
George
G
Eskandar
S Andrea
SA
Wijtenburg
Laura M
LM
Rowland
Geoffrey D
GD
Clarke
Patrick M
PM
Grogan
John H
JH
Sladky
Peter V
PV
Kochunov
D000328:Adult; D000531:Altitude; D016880:Anisotropy; D001274:Atmospheric Pressure; D001921:Brain / Q000000981:diagnostic imaging; D016022:Case-Control Studies; D038524:Diffusion Magnetic Resonance Imaging; D056324:Diffusion Tensor Imaging; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008889:Military Personnel / Q000523:psychology*; D009483:Neuropsychological Tests; D016273:Occupational Exposure; D000070356:Pilots / Q000523:psychology*; D066127:White Matter / Q000000981:diagnostic imaging*