Vestibular adaption to an altered gravitational environment: Consequences for spatial orientation

Vestibular adaption to an altered gravitational environment: Consequences for spatial orientation

Nooij, S.A.E.

Ockels, W.J. (promotor)
Young, L.R. (promotor)

Aerospace Engineering

2008-05-20

Earth's gravity is an omnipresent factor in human life and provides a strong reference for spatial orientation. Changes in the prevailing gravity level, like the transition to weightlessness during space flight, affect spatial orientation and require adaptation of many physiological processes involving the vestibular system (sensitive to linear acceleration and thus gravity). As long as adaptation is not complete, this adaptation process may be accompanied by nausea, visual or self-motion illusions, and disorientation, as experienced by roughly 50% of all space travelers during the first days of spaceflight. Interestingly, the same symptoms can also be experienced on Earth, after sustained exposure to a higher gravitational load in a human centrifuge (i.e., >60 minutes at a level of 3 times Earth's gravity, 3G). And importantly, individual susceptibilities to these symptoms during space flight and following centrifugation are correlated. The finding that the transition from 3 to 1G can evoke the same symptoms as a transition from 1 to 0G indicates that it is not weightlessness per se that causes these symptoms, but that there seems to be a general mechanism for adaptation to an altered gravitational environment. In this thesis the paradigm of sustained centrifugation was used to study the vestibular effects of gravity transitions and the underlying adaptation mechanism. The experiments described in this thesis provided further evidence for a correlation between space motion sickness and sickness induced by sustained centrifugation: astronauts who were susceptible to space motion sickness during spaceflight also suffered from sickness after centrifugation. The role of gravity in the occurrence of the symptoms was underscored by the finding that, after centrifugation, dynamic head movements evoked nausea in susceptible subjects, but only when they changed the orientation of the head relative to gravity (i.e., pitch and roll when erect). In addition, nausea increased with the speed of the movements, the duration of the hypergravity exposure and the level of the applied G-load. Investigation of individual vestibular function parameters indicated that left-right differences within the vestibular system (i.e., differences in sensitivity) contributed to individual susceptibility. Investigation of various ocular responses depending on gravity learned that the eyes' spatial behaviour was less adequate after centrifugation. Furthermore, evidence was found supporting the hypothesis that the integration of sensory signals, required to obtain an adequate perception of gravity during dynamic head movements, was deteriorated. Because the perception of gravity is directly related to the occurrence of motion sickness, this can provide an explanation for the occurrence of these symptoms when tilting head movements are performed after centrifugation. The results of these studies therefore shed light on the mechanism underlying the consequences of gravity transitions. They have direct bearing on the application of artificial gravity during space flight, and can be relevant for astronaut training.

weightlessness
gravity
vestibular system
motion sickness
spatial orientation

http://resolver.tudelft.nl/uuid:027701f4-ee7a-4217-89e2-df61f998a61b

978-90-9022982-9

Institutional Repository

doctoral thesis

(c) 2008 S.A.E. Nooij