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Biomedical subjects

F E Guedry

Publications and source records attributed to F E Guedry.

50 records · Page 3Linked to original sources
PubMedDate not supplied

Space vestibulo-neuroscience in the new century: why proceed in semi-darkness?

With advancing technology, neuroscientists have explored vestibular transducer microstructure and molecular processes, neural pathways of interaction between vestibular visual and proprioceptor systems and neurochemical processes of adaptive change. Progress in space vestibulo-neuroscience will be fostered by focus on interactions among the systems involved in whole-body movement relative to the earth. Description of perceptual and sensorimotor reactions to complex accelerative stimuli during goal-directed and passive movement is crucial to conceptualizing the functional significance of various interactions and viable theory. The vestibulo-ocular reflex is now quantifiable in three dimensions, but description of the dynamics of spatial orientation perception has progressed very little in the 20th century. Much is known about perception of static body tilt, but the dynamics of tilt and movement perception (beyond rotation about an earth-vertical axis) remains relatively unexplored. Innovative procedures and departure from accepted psychophysics are needed. Models developed to predict the dynamics of spatial orientation under complex conditions must be consistent with information at all levels (neural, sensorimotor, and perceptual). To close our eyes to any one aspect of the spatial orientation reaction is to proceed in semi-darkness unnecessarily.

Animals↗
PubMedDate not supplied

Vestibulo-ocular response of human subjects seated in a pivoting support system during 3 Gz centrifuge stimulation.

The vestibulo-ocular reflex (VOR) and spatial orientation perceptions were recorded in 15 subjects during 3 Gz centrifuge runs. These data were obtained to study two issues: (1) to gain insight into reports of asymmetrical disorientation and disturbance during acceleration and deceleration of centrifuge runs like those used to train pilots on the procedures to counteract G-induced loss of consciousness (G-LOC); (2) to study the effects of sustained vertical linear acceleration on the vestibular system. The centrifuge angular velocity profile consisted of a 19 s angular acceleration to 3 Gz that was sustained for 5 min during a period of constant angular velocity, and a 19 s deceleration to 1 Gz. The runs were repeated three times with the subject facing the motion and three times with the subject's back to the motion. The VOR and spatial orientation perceptions from the eight subjects who completed all six runs were analyzed. The total VOR response during acceleration and deceleration was composed of interacting angular (AVOR) and linear components (LVOR). Asymmetries in pitch orientation perception between centrifuge acceleration and decleration were not matched by asymmetries in the total VOR slow phase velocity. During the constant velocity high-G phase of the run, sustained up-beating LVOR (Lz nystagmus) was present in 14 of the 15 subjects. Significant individual differences in Lz nystagmus were found, but the maximum Lz response in our 15 subjects was probably of insufficient magnitude to degrade visual scan of cockpit instruments. Mean magnitudes ranged from 0 to 10 deg/s at 90 s from onset of centrifuge run.

Adult↗
PubMedDate not supplied

Microgravity vestibular investigations: perception of self-orientation and self-motion.

Four astronauts experienced passive whole-body rotation in a number of test sessions during a 7-day orbital mission. Pitch (Y-axis) and roll (X-axis) rotation required subject orientations on the rotator in which the otolith system was at radius of 0.5 m. Thus subjects experienced a constant -0.22 Gz stimulus to the otoliths during the 60 s constant-velocity segments of "pitch" and "roll" ramp profiles. The Gz stimulus, a radius-dependent vector ranging from -0.22 Gz at the otoliths to +0.36 Gz at the feet, generated sensory information that was not interpreted as inversion in any of the 16 tests carried out in flight (12 in pitch and 4 in roll orientation). None of the subjects was rotated with head off-center during the first 33 h of the mission. In the state of orbital adaptation of these subjects, a -0.22 Gz otolith stimulus did not provide a vertical reference in the presence of a gradient of +Gz stimuli to the trunk and legs.

Astronauts↗