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Indirect Estimates of Jaw Muscle Tension in Children With Suspected Hypertonia, Children With Suspected Hypotonia, and Matched Controls

American Speech-Language-Hearing Association
Journal of Speech, Language, and Hearing Research
Authors:
Kathryn P Connaghan at MGH Institute for Health Professions
Kathryn P Connaghan
Christopher A. Moore
Christopher A. Moore
Christopher A. Moore
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Abstract and Figures

Purpose In this study, the authors compared indirect estimates of jaw-muscle tension in children with suspected muscle-tone abnormalities with age- and gender-matched controls. Method Jaw movement and muscle activation were measured in children (ages 3 years, 11 months, to 10 years) with suspected muscle-tone abnormalities (Down syndrome or spastic cerebral palsy; n = 10) and controls (n = 11). Two measures were used to infer jaw tension: a kinematic index of mass-normalized stiffness and electromechanical delay (EMD). The kinematic index used video-based kinematics to obtain the slope of the peak velocity-displacement relationship. The EMD was derived from the interval between the onset of suprahyoid muscle activity and the onset of jaw depression. Results Neither measure differentiated the groups. The kinematic index revealed differences between stressed and unstressed syllables in 3-syllable productions by the participants with cerebral palsy and controls, but not in 2-syllable productions by the participants with Down syndrome and controls. Conclusion This preliminary investigation included the novel application of 2 measures to infer the jaw-muscle tension of children with suspected tone abnormalities. Although the results do not support the hypothesis that suspected muscle-tone abnormalities affect jaw movement sufficiently to influence speech production, considerations for interpreting the findings include methodological limitations and possible compensatory muscle coactivation.
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JSLHR
Article
Indirect Estimates of Jaw Muscle Tension
in Children With Suspected Hypertonia,
Children With Suspected Hypotonia,
and Matched Controls
Kathryn P. Connaghan
a
and Christopher A. Moore
a
Purpose: In this study, the authors compared indirect estimates
ofjaw-muscletensioninchildrenwithsuspectedmuscle-tone
abnormalities with age- and gender-matched controls.
Method: Jaw movement and muscle activation were measured in
children (ages 3 years, 11 months, to 10 years) with suspected
muscle-tone abnormalities (Down syndrome or spastic cerebral
palsy; n= 10) and controls (n= 11). Two measures were used to
infer jaw tension: a kinematic index of mass-normalized stiffness
and electromechanical delay (EMD). The kinematic index used
video-based kinematics to obtain the slope of the peak velocity-
displacement relationship. The EMD was derived from the interval
between the onset of suprahyoid muscle activity and the onset
of jaw depression.
Results: Neither measure differentiated the groups. The kinematic
index revealed differences between stressed and unstressed
syllables in 3-syllable productions by the participants with cerebral
palsy and controls, but not in 2-syllable productions by the
participants with Down syndrome and controls.
Conclusion: This preliminary investigation included the novel
application of 2 measures to infer the jaw-muscle tension of
children with suspected tone abnormalities. Although the results do
not support the hypothesis that suspected muscle-tone abnormalities
affect jaw movement sufficiently to influence speech production,
considerations for interpreting the findings include methodological
limitations and possible compensatory muscle coactivation.
Key Words: cerebral palsy, Down syndrome, children,
speech disorders
Low-level tonic agonist–antagonist muscle activity bal-
anced against intrinsic muscle properties (e.g., elas-
ticity) and joint properties is believed to maintain
muscle length and tension in a state of movement readi-
ness. Although the level of tonic activity required to main-
tain this normal level of muscle tension (i.e., muscle tone)
has not been quantified, individuals presenting with
diminished (hypotonia) or excessive (hypertonia) tone are
readily identified and distinguished during routine clin-
ical examination. Despite its prominence in virtually any
clinical evaluation of neuromuscular integrity, however,
a standard measure of muscle tone has not been widely
adopted. The valid and reliable quantification of muscle
tone is critical to answering basic theoretical and exper-
imental questions that persist with respect to disorders
characterized by abnormal tone: What is the relation-
ship of abnormal muscle tone to functional movement?
Does abnormal muscle tone affect different systems (e.g.,
the limbs vs. oral articulators) by similar or shared mech-
anisms and to similar degrees? What are the ranges of
normal/abnormal muscle tone for various motor systems?
Our understanding of abnormal tone and movement
disorders is essential to advances in theoretically based
treatment. Patients are categorized, treatment is planned,
and progress is measured according to ratings of muscle
a
University of Washington, Seattle
Correspondence to Kathryn P. Connaghan, who is
now at Northeastern University, Boston, MA:
kconnaghan.neu@gmail.com
Christopher A. Moore is now at the Veterans Administration,
Research Division, Rockville, MD.
Editor: Anne Smith
Associate Editor: Steven Barlow
Received June 27, 2011
Revision received January 2, 2012
Accepted May 20, 2012
DOI: 10.1044/1092-4388(2012/11-0161)
Journal of Speech, Language, and Hearing Research •Vol. 56 •123–136 •February 2013 •DAmerican Speech-Language-Hearing Association 123
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