RELATING THE TIME COMPLEX COGNITIVE PERFORMANCE DEGRADES TO PHYSIOLOGIC RESPONSE DURING MODERATE AND SEVERE NORMOBARIC HYPOXIA

INTRODUCTION: Hypoxia-like incidents have risen recently in US military fast jets, often with uncertain cause. To prevent this, a monitoring/alert system is needed, based on a quantitative relationship between physiologic and cognitive responses. METHODS: Informed consent was given by 4 female (29 plus or minus 4yr, 164 plus or minus 7cm, 64 plus or minus 18kg) and 28 male (34 plus or minus 8yr, 182 plus or minus 6cm, 87 plus or minus 9kg) volunteers who trained on the SYNWIN battery (Ver: 1.2.39) in short term memory, math, visual and auditory monitoring tasks. Mean composite scores (CS) were determined every 20s and percent change (%CS) from 12m baseline (BL) calculated. Subjects continually performed SYNWIN while exposed to normobaric altitude profiles: BL(5min), 3048m(10min), 20min moderate hypoxia plateau (MH; 5486m), and recovery(10min) at 12m. After 10min rest, the profile was repeated with a 20min 7620m plateau (severe hypoxia; SH). A Reduced Oxygen Breathing Device (Environics) generated the profiles. Profiles were repeated on two separate days. Pulse oximetry at the finger (SpO2f, Respironics) and forehead (SpO2h, Masimo RAD87) were recorded. Relative regional cerebral tissue oxygenation was measured (Nonin Equinox) and percent change relative to BL determined (%rSO2). Exposures were terminated and 100% O2 provided (O2) if SpO2f=60%. Polynomial regression models of %CS over time for MH and SH were developed and corresponding mean SpO2 and rSO2 calculated. RESULTS: %CS models were created using 45 MH (r2=.75) and 44 SH (r2=93) exposures. At MH, %CS fell by 25% at 487s (SpO2f=75.6 plus or minus 5.8; SpO2h=80.4 plus or minus 7.2; %rSO2=20.1 plus or minus 3.3%) and 33% at 907s (SpO2f=72.5 plus or minus 7.5; SpO2h=79.1 plus or minus 7.6; %rSO2=21.6 plus or minus 3.0%). At SH, %CS fell by 25% at 73s (SpO2f=77.5 plus or minus 6.0; SpO2h=80.3 plus or minus 5.8; %rSO2=17.4 plus or minus 5.2%), 33% at 109s (SpO2f=72.0 plus or minus 5.7; SpO2h=76.5 plus or minus 6.5; %rSO2=21.2 plus or minus 4.1%), and 50% at 1 70s (SpO2f=67.4 plus or minus 4.4; SpO2h=74.3 plus or minus 6.3; %rSO2=24.0 plus or minus 4.3%). %CS recovery times at MH were 52.0s(25%), 101.5(15%), and 448.0s(5%); after physiologic recovery, i.e., SpO2>90% (SpO2f=24.2 plus or minus 45.0s; SpO2h=28.8 plus or minus 28.0s; rSO2