Abstract
Background.
Spasticity is common in patients with stroke, yet current
quantification methods are insufficient for determining the relationship
between spasticity and voluntary movement deficits. This is partly a
result of the effects of spasticity on spatiotemporal characteristics of
movement and the variability of voluntary movement. These can be
captured by Gaussian mixture models (GMMs). Objectives. To
determine the influence of spasticity on upper-limb voluntary motion, as
assessed by the bidirectional Kullback-Liebler divergence (BKLD)
between motion GMMs.
Methods. A total of 16 individuals with
subacute stroke and 13 healthy aged-equivalent controls reached to grasp
4 targets (near-center, contralateral, far-center, and ipsilateral).
Two-dimensional GMMs (angle and time) were estimated for elbow extension
motion. BKLD was computed for each individual and target, within the
control group and between the control and stroke groups. Movement time,
final elbow angle, average elbow velocity, and velocity smoothness were
computed.
Results. Between-group BKLDs were much larger than
within control-group BKLDs. Between-group BKLDs for the near-center
target were lower than those for the far-center and contralateral
targets, but similar to that for the ipsilateral target. For those with
stroke, the final angle was lower for the near-center target, and the
average velocity was higher. Velocity smoothness was lower for the
near-center than for the ipsilateral target. Elbow flexor and extensor
passive muscle resistance (Modified Ashworth Scale) strongly explained
BKLD values.
Conclusions. Results support the view that
individuals with poststroke spasticity have a velocity-dependent
reduction in active elbow joint range and that BKLD can be used as an
objective measure of the effects of spasticity on reaching kinematics.
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