Antiorthostatic posture as an earth model of the effect of microgravity on the human body.

We examined the horizontal and vertical component of diagonal optokinetic nystagmus (DOKN) in sitting posture and in the last 15 minutes of antiorthostatic posture at -30 degrees lasting 3 hours. The antiorthostatic posture is suited to the earthy model of the fluid shifting observed in microgravity. We found that the frequency of the vertical component of DOKN is rarer in antiorthostatic posture than in sitting posture. Moreover, the amplitude of the vertical component of DOKN is lower in antiorthostatic posture than is the amplitude of the horizontal component. According to our examinations, we suppose that the frequency and amplitude of vertical OKN are directed by different cerebral structures. Furthermore, we found that the heart rate becomes slower and the diastolic pressure is augmented after antiorthostatic posture and visual stimulation.