Gravity-induced loss of consciousness (G-LOC) is a major threat to fighter pilots and may result in fatal accidents. High +Gz (head-to-foot direction) acceleration force induces cerebral blood loss and results in loss of peripheral vision, loss of central vision (black out), and G-LOC. We tried to establish a formula to predict G-LOC using cerebral oxyhemoglobin (oxyHb) value, height, weight, and body mass index (BMI). We analyzed 249 human centrifuge trainees be measured cerebral oxyHb value during 2008 to 2012. Trainee was exposed to two centrifuge profiles. One is 4G–15s, 5G–10s, 6G–8s, and 7G–8s, without G-suits (60 s interval and onset rate of 1G/s). Other one is 8G-15s with onset rate of 6G/s, with G-suits. We measured trainee’s cerebral oxyHb value using near infrared spectroscopy (NIRS) (NIRO-150G, Hamamatsu Photonics K.K., Hamamatsu, Shizuoka, Japan). The following parameters were analyzed. A) The baseline values as an average over 30 s before +Gz exposure. B) Maximum value of oxyHb during +Gz exposure. C) Minimum value of oxyHb during +Gz exposure. D) Rate of change from Maximum to Minimum value of oxyHb (rate of change). Statistical analysis was performed using logistic regression analysis to establish formula for predicting G-LOC. The trainees’ age was 24.1 ±1.7 (S.D.) (range, 22～30) years old, height was 171.9±4.7 (159～187) cm, weight was 66.6±6.4 (50～88) kg and BMI was 22.5±1.8 (19.15～27.76). In 249 trainee, 34 (13.7 %) had G-LOC and 215 (86.3 %) did not have G-LOC. G-LOC was significantly associated with BMI (odds rate, 0.74; 95% CI, 0.57～0.98; p = 0.03.) and Rate of change of Maximum to Minimum value of oxyHb (odds rate, 0.50; 95% CI, 0.38～0.66; p < 0.01.) by Logistic regression analysis. The formula to predict G-LOC is following: Log (P/1−P) = −0.2951 X (BMI) −0.6919 X (Rate of change) +2.9701. P represents percent probability of G-LOC. (decision level: 0.15, sensitivity: 67.6%, specificity: 81.4%, accuracy: 79.5%) Our results suggest that BMI and Rate of change of cerebral oxyHb was predictive factors for G-LOC. This investigation was performed with limited factors available. Further factors to enhance accuracy may be needed.
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