Transcript lecture 12

Laryngeal Physiology
Valving for Life: NonSpeech
1. Breathing:
– Airway open
– Three laryngeal valves open
(supraglottal cavity, the false vocal folds
& true vocal folds)
– Quiet respiration= true folds open to
intermediate position
– Forced respiration= Abducted to lateral
position
Valving for Life: NonSpeech
2. Swallowing:
• Guards against entrance of any
substance into the airway
• Swallowing reflex:
– larynx elevates,
– epiglottis drops to to cover larynx,
– aryepiglottic folds tense,
– vocal folds adduct
Valving for Life: NonSpeech
3. Pressure Activities (sneezing, coughing, lifting)
– Require alveolar pressure
– Compression of air by respiratory pump
– Dependent on how tightly the laryngeal valve can be
closed
– Without airway resistance, thoracic compression
produces only expulsion of air
– Cough- deep inhalation, abducted vocal folds,
elevation of larynx, significant subglottal pressure
(tissue recoil and expiratory muscles)
Valving for Speech
• Modified use of laryngeal valve
• Breathing adjustments of the larynx are
modified least
• Swallowing reflex prevents speech
• Pressure reflex evolved solely for speech
• Start phonation: adduct vocal folds, moving
them into airstream, hold this position as
aerodynamics of phonation control vibration
Valving for Speech
1. Mechanics of voiceless sounds :
– Voiceless consonants (first sounds of: pad, tad, cad)
• Laryngeal valve open
• Airflows unobstructed
• Restricted partially by tongue or lips
– Whispering
• No voicing occurs
• V.F’s offer resistance to airstream, partially adducting V.F’s
• Vibrating glottal edges bordering vocalis muscle are stiffened
and positioned far apart to prevent vibration but vocal
processes are towed in ( by LCA), the cartilaginous portion is
separated to form the posterior glottal chink (permits air
through glottis without fold vibration)
The Glottis- Whispering
Whispering Triangle
Cartilaginous
Glottis
Muscular Glottis
Valving for Speech
2. Mechanics of glottal vibration:
vibratory cycle- single vibration of the vocal folds
(or glottal cycle)
“Begins when subglottal pressure (Ps )
overpowers fold resistance just enough for the
v.f.’s to first blow open.”
*opening phase: v.f. continue to blow apart
* closing phase: escape of air reduces Ps
enough for fold resistance to overpower
airflow, then close.
Glottal Cycle
opening phase
closing phase
open phase
closed phase
• Arrows represent driving air pressure changes
• Notice that the vocal folds are always in transition
Valving for Speech
• Mechanics of glottal vibration cont.
1. Two ratios to describe the features of
vibration:
* speed quotient (SQ)- the ratio of the
durations of the opening phase to the
closing phase (opening/closing).
* open quotient (OQ)- the ratio of the
duration of openness to the duration of the
entire cycle (open/entire cycle)
Valving for Speech
• Mechanics of glottal cycle cont.
1. V.F.’s vary in compliance: How
absorptive of force & vary in
complexity of vibratory movement.
*Compliance: Closed phase is period
of v.f. absorption (time of closed
phase= force of collision). More
compliant = more absorption
Effects of Compliance on Glottal Cycle
Steel Balls
Point of
Impact
Compliant
Absorption of
Impact
Rubber Balls
Open Phase
Closed Phase
Closing Phase
Opening Phase
Valving for Speech
• Mechanics of glottal cycle cont.
– Complexity in Vibratory Motion:
*Vertical Phase Difference:
-V.F.’s open and close from bottom to
top
-They also open from back to front and
close from front to back
* Also, another vibratory complexity is the
motion of the mucous membrane covering
the true vocal folds
Movement of vocal folds
Spread of glottal opening
Vertical Phase difference
• Note how the vocal folds open from bottom to top
& back to front.
Valving for Speech
3. Vibratory Forces:
• Aerodynamic-myoelastic theory of phonation“Glottal vibration is a result of the
interaction between aerodynamic forces &
vocal fold muscular forces.”
*Aerodynamic forces-Bernoulli Effect: as velocity of a gas
or liquid increases, pressure
decreases.
Bernoulli Effect
• Trachea & laryngeal airway
as a freeway
• molecules of air= cars
• closer the molecules (cars),
slower they move
• faster they move the farther
apart they are spaced (lower
pressure)
• faster air moves through
glottis, farther molecules are
apart & exert less force on
v.f.’s
Molecules
(Cars
accelerate)
Compressed
molecular
traffic
Valving for Speech
• Vibratory Forces cont.
* Myoelastic ForcesThe opposing myoelastic
(muscular & elastic tissue)
forces provides the vertical
phase difference essential for
phonation.
* Myoelastic component cont.1) The glottal edge, particularly the loose mucosal
covering functions as two separate but
interconnected masses, one below the other,
2) These two masses are actually the upper & lower
portions of the mucous membrane & the
underlying vocalis muscle,
3) When lower portion is pushed aside by air
pressure, the upper portion is dragged along,
4) The strength of the connection between these two
masses is the mechanical coupling stiffness
Mechanical Coupling Stiffness
• Upper & lower
portions work
together (coupled),
• Remember: The
masses are the vocal
folds,
• One of several
muscular forces
involved with
phonation.
Upper
Mass
Lower
Mass
Upper Mass
Lower Mass
Other Muscular Forces
• All provide resistance to airflow-
1) Stiffness or “longitudinal tension”- inc. in
muscle stiffness increases resistance; elongation
merely thins the vocalis muscle,
2) Mass resistance- thickness in the vocalis
muscle, more mass in the cords the more force
required to blow them apart,
3) Viscous forces- more viscous the vocal folds,
the more they decrease the velocity of movement
they are forced to make, inc.. resistance to
aerodynamic forces
Summary of AerodynamicMyoelastic Theory
• “v.f. vibrations are dynamic
interchanges of intraglottal
pressure between the folds that
force them apart and their
mechanical resistance to this
pressure.”
Summary Cont...
• Beginning of glottal cycle:
1) Intraglottal pressure exceeds atmospheric
pressure above the folds & forces open a
small glottal chink,
2) Air flows through the chink; molecules are slow
in the trachea than increase velocity traveling
through the glottis (i.e. Bernoulli slide),
3) Air molecules accelerate and start to move
farther apart,
4) Pressure against upper portion of the folds
decreases, but remains high against the lower
portion (where molecules are still
compressed in a “traffic jam”),
5) Therefore, the upper glottis is not blown open
by pressure but “dragged” along by the
stiffness of mechanical coupling,
6) Lower potion is where the intraglottal pressure
forces the folds apart,
7) Aerodynamic force continues to open the
glottis,
8) Closure when resistance exceeds intraglottal
pressure.
Reading/Assignments
• Seikel: Pgs.157-164
• Dickson: Pgs. 134-139