Developmental issues
• Laryngeal structure and function
• Vocal tract structure and function
• Respiratory structure and function
Premise
• As SLPs, we
“operate” on the
larynx and other
phonatory structures
• Therefore knowledge
of developmental
issues in these
structures is important
Laryngeal structure
(and vocal tract)
•
Neonatal compared to adult:
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Pharynx short
Cricoid cartilage is high (C4)
Tip of the epiglottis is high (C1)
Approximation of epiglottis and soft
palate thought to allow sucking and
simultaneous respiration
Hyolaryngeal area is compact
Age 2: Lower border of larynx
descends to C5
Age 6: Lower border of larynx
descends to C6
Age 15: Lower border of larynx
descends to final position C6-7; thyroid
cartilage and hyoid bone separate
during descent
Epiglottis: Increases curvature until age
3, then gradually flattens
•
Isaacson, 1996
•
Implication: Vocal tract – source interactions
will vary with age; details not well studied
Laryngeal structure
• Neonatal vs adult,
cont’d
• Implication: Care in
interpretation of
images
– Aryepiglottic folds thick
and bulky
– Arytenoids appear
prominent
– Glottis is 7 mm AP and
4 mm lateral
– Isaacson, 1996
Laryngeal structure
• Neonatal vs adult, cont’d
– Collagen: About 51% of
the collagen found in adults
(Hammond et al., 2000)
– Elastin: About 23% of the
elastin found in adults
(Hammond et al., 1998)
– Differentiation of superficial
and deep layers of the
lamina propria not present
(no ligament) (Ishii et al.,
2000)
• Image from Gray, 1996
• Implication:
Anatomical basis
for high pitches in babies?
Possibly greater cushioning on VF
impact? However, might injury to
the BMZ in childhood show up as
predisposition to clinical entities
later? (Gray, personal
communications)
Laryngeal structure
• Neonatal vs adult,
cont’d
– Hyaluronic acid
(glycosaminoglycan;
“cushioning”): actively
produced in the
maculae flavae of
infants
– Sato et al., 2001
• Implications: Infant larynx
may be protected from
phonotrauma due to high
proportion of HLA?
Laryngeal structure
• Neonatal vs adult, cont’d
– Fibroblasts: Mostly oval in
newborns and spindleshaped in adults. Inactive
in producing fibers in
newborn.
– So fibroblasts and macula
flava may contribute to
development of ligament
over time.
– Hirano et al., 1999
• Implications: Infant
larynx may be
protected from
phonotrauma by
reduced rate of fiber
formation
Laryngeal structure
• Children,
development
– Age 5: Dense area
seen in the anterior
and posterior maculae
flavae; longitudinal
fibers found between
the maculae.
– Age 10: Differentiation
of superficial versus
deep layers of the
lamina propria
– Age 17: The layered
structure of the lamina
propria is complete
around 17 years of
age.
– Ishii et al., 2000
Laryngeal structure
• Neonatal vs adult, cont’d
– Overall implications: Some
critical differences between
architecture of the lamina
propria in infants versus
adults may result in
protective mechanisms for
infants
– Evolutionary issues
Laryngeal structure
• Child, cont’d
• Prepubertal vs pubertal
larynx, male and female
(ages 9-18; Kahane,
1978)
• Angle of the thyroid
cartilage decreases in
boys with age; therefore
the relative posterior
glottal gap is reduced,
compared to the
relative gap in females
•
PGG is thought to contribute to
the biomechanics of impact stress,
greater in females (women; e.g.
Morrison & Rammage, 1993)
Laryngeal function
• Summary
• Infant vocal folds may
have protection
against phonotrauma
• Risk may increase
with time from infancy
• These speculations
match clinical
observations
Vocal tract structure
• Dimensions increase
• Formant frequencies
decrease
• Implications: Sourcefilter interactions
change quantitatively
• Details not well
worked out
specifically for
children
Vocal tract/articulatory function
• Ages 1-6: Changes in
coordinative relationships
of articulators
– Young children: Jaw
predominated
– Older children: Increasing
independence of upper and
lower lip; increasing use of
lip movement for bilabial
closure
– Green et al., 2000;
Green et al., 2002
Vocal tract/articulatory function
• Ages 1-6: Changes in
coordinative relationships
of articulators
– Young children: Jaw
predominated
– Older children: Increasing
independence of upper and
lower lip; increasing use of
lip movement for bilabial
closure
– Green et al., 2000;
Green et al., 2002
• Implication: Evidence is
seen of increasing
differentiation in motor
control
– Is one implication that very
young children may have
difficulty differentially
altering voice independent
of articulation, reducing a
benefit of voice therapy?
– Or it is possible that voice
therapy would need to take
into account this coupling
in some as yet unclear
fashion?
Respiratory structure
•
•
Decreasing compliance of rib cage
Changes in general shape and
orientation of rib cage
• Papastamelos et al., 1995; Sharp
et al., 1970
•
Toddlers
– Rest breathing:
• Paradoxing in inspiration (collapse
of chest), probably due to high rib
compliance (Gaultier et al., 1987)
•
Toddlers to children
– Rest versus speech breathing (15
mo):
• Rest: Relative synchrony between
rib and abdomen
• Speech: Oppositional movement
between rib and abdomen in
speech breathing
– Variability:
• Large intra- and intersubject
variability (5 wk to 1 yr; 1 yr to 3
yr)
» Moore et al., 2001; Boliek
et al., 1996, 1997)
Respiratory function
• Toddlers and children (948 mo)
– Increasing independence of rib
and abdomen during speech (not
rest) breathing (coupling
decreased 15% over 3 yr)
– Increasing rib expansion in
speech (7% over 3 yr)
– Increase in oppositional
movement of rib and abdomen,
possibly favorable
biomechanically
– Changes were gradual,
suggesting attribution to structural
changes, not motor control
changes
» Moore et al., 2004
• Implication: With age,
increased capability to
generate increasing Ps,
and thus increasing VF
impact stress??
– E.g. Jiang & Titze, 1994
Summary
• Molecular changes in VF
structure may increase
potential for phonotrauma
with age, after infancy, in
children (hyaluronic acid;
fiber generation; lamina
propria differentiation)
• Macroscopic changes
(relative PGG) may be
further protective against
phonotrauma in the male
larynx with increasing age
• Decreases in rib cage
compliance and
increasing oppositional
movement of rib cage
and abdomen, to stabilize
(and increase?) Ps, may
further increase potential
for phonotrauma with
age, after infancy, in
children
Summary
• Stated differently,
from a basic science
perspective, children
appear to have
greater risk of
phonotrauma with
advancing age
• This result seen
clinically as well
Final note
• Target of barely
ad/abducted VFs
appears relevant for
children as goal of
therapy, as for adults
– Preliminary data, D.A.
Berry, personal
communication