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 Gravity-induced loss of consciousness (G-LOC). G-LOC is a major threat to fighter pilots and may result in fatal accidents. The brain has some ability to tolerate transient ischemia and to prevent loss of consciousness during high +Gz exposure. This has been named as the functional buffer period. The functional buffer period is approximately 4-5 seconds against any +Gz exposure. The purpose of the present study is to measure trainees’ cerebral oxyhemoglobin (oxyHb) concentration in the functional buffer period that was the period of five seconds after the onset of high +Gz and identify the differences between trainees with G-LOC and those without. We analyzed cerebral oxyHb concentration of 124 human centrifuge trainees who was trained during 2008 to 2012. The trainees were classified into G-LOC and Non-G-LOC group. Each group had same number of trainees in the following categories.
A) 6G (1G/s, without anti-G suits): N=34 (N=17 in each group).
B) 7G (1G/s, without anti-G suits): N=62 (N=31 in each group).
C) 8G (6G/s, with anti-G suits): N=28 (N=14 in each group).
We measured trainee’s cerebral oxyHb concentration using near infrared spectroscopy (NIRS) (NIRO-150G, Hamamatsu Photonics K.K., Hamamatsu, Shizuoka, Japan). The cerebral oxyHb concentration was measured before Gz load as the baseline, and during five seconds from the onset of high Gz. The sampling rate was set at 2Hz.
A) 6G (1G/s, without anti-G suits): The cerebral oxyHb concentration were significantly lower in the G-LOC group(－2.1±9.4) compared to the Non-G-LOC group (4.5±9.4).
B) 7G (1G/s, without anti-G suits): The cerebral oxyHb concentration was not significantly different between the groups.
C) 8G (6G/s, with anti-G suits): The cerebral oxyHb concentration in the groups showed a significantly different time course. At 0 sec after the high Gz onset, the cerebral oxyHb were significantly higher in the G-LOC group (18.6±12.1) compared to the Non-G-LOC group (10.4±8.3). However, the G-LOC group showed a sharp decrease until 4.5 seconds.
In the future, it is necessary to find the specific trend of cerebral oxyHb concentration and prepare to prevent G-LOC.