Abstract
The cerebral oxygen status and/or concentration changes were measured by a non-invasive technique using the near infrared spectroscopic method for 14 male volunteered subjects. The subjects were exposed to a gradual onset rate run (GOR) and rapid onset rate run (ROR)+Gz acceleration for the purpose of evaluating the cerebral oxygen status and concentration changes until physiological end point (the point when peripheral light loss emerges). The near infrared oxygenation monitor was used in order to measure the concentrations of oxygenated hemoglobin (HbO_2), reduced hemoglobin (Hb), oxygenated cytochrome oxidase (CtO_2), and total hemoglobin (tHb) in the brain. It was found that the HbO_2 and tHb were clearly reduced by +Gz acceleration within the brain. On the other hand, the changes in Hb and CtO_2 were inconsistent among the subjects. At the physiological end point, the mean levels of decreased concentration (threshold) of HbO_2 ranged from 9.3 to 29.0 μmol/l (of the brain tissue) among the subjects, suggesting that there may be inter-individual differences in the tolerance for +Gz acceleration. Strong correlation (r=-0.95±0.02, n=18) was noted between the change in the cerebral concentration of HbO_2 and +Gz value for a total of 18 measurements in the 8 subjects during GOR +Gz accerelation. This close relationship suggest that +Gz acceleration may directly affect cerebral blood flow and/or proportions of oxygen-saturated hemoglobin within the brain. The non-invasive technique using near infrared spectroscopic method will be useful for basic research on cerebral circulation or the physical check-up for aviators.
