Temporary cerebral histic hypoxia in simulated microgravity.
The authors determined in their previous examinations that the vertical component of diagonal optokinetic nystagmus (DOKN) decreases considerably more in the conditions of hypoxia and antiorthostatic posture than does the horizontal component. Relying on these findings, they reasoned that the tectal and pretectal gaze centers, which organize vertical eye movement, are more sensitive to both hypoxia and antiorthostatic posture than is the pontine gaze center, which directs horizontal eye movement. In their present examinations, the authors sought to discover how cranial shifting of body fluids alters the DOKN and cardiopulmonary dynamics. They established that, at-30-degree antiorthostatic posture during 3 hours' loading, the diminution of pulse rate and systolic blood pressure is accompanied by continuous enhancement of diastolic blood pressure, diminishment of the carbonometric value, and augmentation of respiratory rate. The disturbances of DOKN, which mimicked previous similar findings under conditions of hypoxia and antiorthostatic posture, may be caused by the hypocapnia that is induced by antiorthostatic posture and that produces histic hypoxia. However, hypocapnia does not exclude the possibility of cerebrovascular injury, which was detected during animal experiments in microgravity or in simulated microgravity. To resolve this issue ultimately, further investigations are necessary.