Evaluation of dynamic postural control for experimental studies and medical testing
of astronauts is supported using modified and enhanced versions
of the commercially available EquiTest computerized dynamic
posturography system developed by NeuroCom, International
(Clackamas, OR, USA) for clinical assessment of disorders
in balance control.
The standard EquiTest system consists of a computer-controlled,
motor-driven support surface and visual surround. Force
transducers beneath the support surface can be used
to servo-control the pitch of the support surface and/or
visual surround  to
follow the sway of a subject, thus decoupling proprioceptive
and/or visual sensory feedback respectively from the
true orientation of the subject. The support surface
can also be driven to provide rapid (~0.4s) constant
velocity perturbations to the postural control system
by altering either the pitch or the fore-aft horizontal
position of the platform.
Image right: Posture Platform used to test balance control
In order to improve the sensitivity
of the posture platform system, and to improve our ability
to interpret its output our EquiTest systems has been modified
to monitor and record 3-dimensional multi-segment kinematics
of sway using an OPTOTRAK 3020 active marker motion analysis
system developed by Northern Digital, Inc. (Waterloo, Ontario,
Canada). This system is currently equipped to track up to
twelve infrared light emitting diodes at a maximum sampling
frequency of 3500 Hz divided by the number of markers being
used. Other EquiTest systems are equipped with a swaybar
system to measure horizontal (anterior-posterior) positions
of the hips and shoulders using rotational potentiometers.
Both systems have Watson ARS-C241-A1 angular rate sensors
(Eau Claire, WI, USA) to measure pitch and roll velocities
of the head, and an EMG system capable of recording the activity
of six muscle groups.
|
