The body’s balance system adapts to space’s lack of gravity, and astronauts often cannot coordinate body movements and stabilize movement upon return to Earth. Dr. Conrad Wall III is evaluating ways to ameliorate these problems by studying body, head and eye movements while patients walk on a moving platform, on a circular treadmill and on ascending or descending stairs. He is also determining the effectiveness of a prosthesis device and exercises designed to combat problems with balance.
Overview
Advanced Techniques to Assess and Counter Gait Ataxia
Principal Investigator:
Conrad Wall, III, Ph.D.
Organization:
Harvard - Massachusetts Eye and Ear Infirmary
Harvard-MIT Division of Health Sciences and Technology
Technical Summary
The overall goals of this project are to develop "countermeasure assessment criteria" to evaluate recovery from disturbances, and during turning, circular walking and ascending and descending stairs. We also consider countermeasures using a balance prosthesis and dynamic exercises designed to challenge and increase subjects' balance. We will determine the sensitivity of the countermeasure assessment criteria in evaluating effects the prosthesis and the exercises on postural stability and locomotion. Using human subjects, the specific aims of this project are to:
- Study body and head movements during precise perturbations of gait during continuous straight locomotion.
- Study body, head and eye movements during continuous straight or circular locomotion on a circular treadmill.
- Study body, head and eye movements during ascending and descending a staircase.
- Study body, head and eye movements during standing, linear walking and treadmill walking with a balance prosthesis designed as a countermeasure for vestibular adaptation.
- Study the effect of dynamic balance exercises for vestibulopathic subjects upon their ability to stand quietly and to recover from mild perturbations.
Key findings of the project
We have developed an experimental protocol that introduces a calibrated disturbance to the foot during the support phase of normal locomotion. This provides a means for the objective quantification of locomotor response dynamics that are known to be altered in astronauts upon return from exposure to microgravity but for which no current test exists. Returning astronauts whose orientation mechanism has been distorted and patients having balance disorders (vestibulopathies) that may well affect their orientation mechanism was expected to have different recovery trajectories than healthy normals. This is has now been demonstrated for vestibulopathic subjects. A simplified version of our research device is now being developed for use in evaluating the functional mobility of astronauts by scientists at the Johnson Space Center.
One of our working hypothesis was that profound impairments of posture, gaze and locomotion stability are caused by alterations in compensatory and orientation mechanisms that are generated in the central vestibular system from motion inputs. During exposure to altered gravity, the motion inputs from the otolith organs are "distorted" compared to the on-earth conditions. These distortions, in turn, cause both inappropriate body head and eye movements and an altered sense of orientation, which degrades stability during locomotion. We compared motions of the body during walking along a straight line with body motions while walking along a curved path. In the latter condition subjects accelerate in toward the direction of the curve, which introduces an inertial component which may or may not effect measures of their body orientation in space. Our results show that compensatory eye, head and body movements stabilize gaze during straight walking, while orienting mechanisms direct the eyes, head and body to tilts of the resultant of gravitational and centripetal acceleration in space during turning. This finding in normal subjects can now be compared to subjects with known impairments in their balance system or to returning astronauts to determine whether or not such individuals can successfully align parts of their bodies in an appropriate way while turning.
We have developed the simplified precursor to a balance aid. It uses body mounted motion sensors to estimate the tilt of the subject. This estimated tilt is coded and fed back to the subject using an array of small, non-invasive tactile vibrators mounted on the skin. The application of vibrotactile display of body tilt demonstrates for the first time (to our knowledge) that tilt estimates derived from body-mounted motion-sensing instruments can actually be used to reduce sway in subjects who have documented deficits in their balance (vestibular) function. The single most important finding was that subjects who repeatedly fell under challenging balance conditions were able to stand with the use of this aid.
This project's funding ended in 2004