This document provides an overview of larynx physiology including: - Anatomy of the vocal folds and their layers, nerve supply, and functions such as breathing, swallowing, and coughing. - The biomechanics and myoelastic-aerodynamic theory of phonation involving vibration of the vocal folds driven by subglottic air pressure. - Assessment techniques for laryngeal function including videolaryngostroboscopy, contact endoscopy, and narrow band imaging to visualize mucosal waves and vascular patterns.

1. PHYSIOLOGY OF LARYNX
Dr. Bikram B. Karki
ENT - HNS, MTH

2. VOCAL FOLD ANATOMY
• During normal modal phonation,
mucosa undulates freely over underlying
vocal ligament and vocalis muscle.
• Hirano’s - histologic studies showed that
• Mucosa and muscle are separated by
specialized layer of connective tissue
that serves as a shock absorber

3. NERVE SUPPLY

4. • The larynx has a number of functions
• To prevent foreign material from entering airway (aspiration)
• Acts as vibrator for generating sound
• Acts as a valve that can control air pressure and airflow
• Fundamental importance during breathing, weight bearing

5. LARYNGEAL MECHANORECEPTORS
• Free fibrils and terminal filaments enclosed in capsules
• Embedded in laryngeal tissues at sites sensitive to muscle stretch
and airflow pressures
• Wyke, postulated that mechanoreceptors are found in three sites:
1. Mucosal mechanoreceptors
• Corpuscular nerve endings
• Sensitive to stimuli of muscle stretch, air pressure level, liquid and
touch
• Discharge impulses - afferent fibres of vagus

6. 2. Articular mechanoreceptors
• Capsules of the articulatory joints
• Existence and function of this group remain controversial.
3. Myotatic mechanoreceptors
• Extrinsic and laryngeal muscles
• Tone of laryngeal muscles depends on myotatic reflex

7. FUNCTIONS OF THE LARYNX
• Swallowing (deglutition)
• During swallowing primary function of larynx - prevent food and
liquid entering the airway.
• This is achieved by means of
1. Sphincteric action of AE fold
2. True VF and
3. Ventricular folds,
which occurs simultaneously with elevation of larynx.
• Laryngeal elevation - control pressures and function of
cricopharyngeal sphincter

8. • Vocal fold adduction during swallowing - average approximately
2.3 seconds
• Airway is also protected by epiglottis - which covers the laryngeal
entrance
• Clinical correlates
• If laryngeal elevation is impaired
• Peri-swallow aspiration
• Cricopharyngeal opening is limited

9. COUGH REFLEX
• Protective reflex which ejects
mucus and foreign material from
lungs
• Cough can be
1. Voluntary action or
2. Reflexive response
• Consist of 3 phases-
• Inspiratory
• Compressive
• Expulsion

10. • First phase -inspiratory
• Glottis abducted, air inspired
• The second phase - compressive
• Glottis close, expiratory muscle contract
• Third phase – expulsion
• Air pressure buildup below adducted fold as diaphragm ascends
spasmodically
• Abduction of glottis
• Sudden and rapid outflow of air at speeds of as high as 10 l/sec.

11. EFFORT CLOSURE
• Provide a stable fulcrum for the upper limbs.
• For exertion involving use of arms,
VF are firmly adducted
preventing expulsion of air & collapse of chest wall
• Also occur during childbirth and defecation
• Clinical correlates
• Laryngectomy/ true VF palsy patients:
Weight bearing difficulty because of
inability to close glottis effectively

12. THE NEUROANATOMY OF PHONATION
• Dependent upon integrated functioning CNS and PNS
• Cortical loci - voluntary phonation
• Subcortical representation – 1. Involuntary phonation
2. Reflex laryngeal function
• Periaqueductal grey matter (PAG), a region of the mid-brain,
1. Crucial site for mammalian voice production
2. Integration of cortical and subcortical aspects of language
3. Production of involuntary or emotional sounds

13. NEURAL PATHWAY FOR VOLUNTARY
VOCALIZATION
• Arise in pre-central gyrus of motor cortex
• Fibres descend as part of corticobulbar
tract
(Part of pyramidal system or ‘direct
activation’ tract)
Medulla
• Some fibres synapse with ipsilateral vagus
nucleus

14. • The vagal nuclei, in nucleus ambigus (the reticular formation of
the medulla)
also contain 9 and 11 cranial nerve elements
Ipslilateral and contralateral vagus
Supply laryngeal muscles
• UMN do not govern isolated muscles, but groups of muscles.
• Frontobulbar portions of pyramidal tracts connect with cranial
nerves ix–xii, thus control phonation, articulation and respiration

15. THE BIOMECHANICS OF PHONATION
• VF provides visco-elastic mechanical properties - producing voice
• When larynx is at rest and respiration is quiet
VF abduct on inspiration
slightly adduct on expiration.
• On forceful inspiration – full abduction of VF
• Larynx descend on inspiration
ascends on expiration

16. INITIATION OF VOICE
• Pre-phonatory inspiratory phase
• VF rapidly abduct to allow intake of air
• Subsequently, VF are adducted – due to contraction of LCA muscle
• Subglottic air pressure increases below adducted VF
• Blows them apart, thus setting in motion vibratory cycle -
phonation
• Phonation threshold pressure
• Amount of air pressure required to begin voicing
• Factors affecting :
• Viscoelastic properties of VF
• Size and tension of VF

17. THE VIBRATORY CYCLE
• Consists of three phases:
1. Adduction
2. Aerodynamic separation and
3. Recoil
• Begins with vocal folds closed
• As subglottic air pressure increases - VF separates from inferior
border
• When they finally separate at superior margin, puff of air released
• Resulting negative pressure in glottis (bernoulli effect) results VF
closing rapidly - inferior VF margins closing first
• Mucosal wave travels- inferior to superior margin

19. VOCAL REGISTERS
• Registers are defined in term of laryngeal behaviour
• Governed by degree of contraction of vocalis muscle

20. PHONATION
• Neurochronaxic theory
• Husson (1950)
• Glottic vibrations were caused by rhythmic nerve impulses to
larynx
• Each vibratory cycle was caused by a separate neural impulse
• Fallacies
• Vocal folds would not vibrate synchronously as longer course of
RLN in left
• If neurochronaxic theory were true, patients with tracheotomies
would be able to phonate - but they cannot

21. “BODY-COVER” THEORY
• Two-mass model
• “Body” of VF – vocalis muscle - relatively static
• “Cover” of VF – vocal mucosa - wave is propagated – blown by
expiratory air
• Vibration of mucosa does not correspond directly to that of rest of
vocal fold
• Mucosal wave begins on inferomedial aspect of vocal fold and
moves rostrally

22. THE MYOELASTIC-AERODYNAMIC THEORY
• Van den berg(1950)
• Myo - muscular involvement
• Elastic - ability to return to original state
• Aero - air pressure and flow
• Dynamic - movement and change
• Describes voice production as a combination of muscle force
(myo), tissue elasticity (elastic), and air pressures and flows
(aerodynamics)
• Widely accepted theory

23. • Process of phonation
• Begins with inhalation of air
• Glottic closure
• Subglottic pressure to increase until vocal folds are displaced
laterally
• Factors which bring glottis back together
1. Pressure decrease
2. Elastic forces in VF
3. Bernoulli effect on airflow
• When VF return to the midline, pressure in trachea builds again -
cycle is repeated

24. ASSESSMENT OF LARYNGEAL FUNCTION
• VIDEOLARYNGOSTROBOSCOPY (VLS)
• Evaluation of visco-elastic properties of
phonatory mucosa
• Principle
• Flashes of light from stroboscope are synchronized to VF vibration
at a slightly slower speed
• Allowing examiner to observe VF vibration during sound production
in slow motion

25. • Stroboscopy systems
• Endoscope
• Stroboscopic light source
• Camera and lens
• Microphone – picks up frequency
• Video recorder
Standard 70-degree rigid
strobolaryngoscope
Camera attachment
with mounted
microphone.
flexible laryngostroboscope

26. • Clinical applications
• Several parameters may be evaluated
• Glottal closure
• Mucosal wave
• Amplitude
• Periodicity
• Symmetry
• Fundamental frequencies

27. Notice that mucosal waves originate upon closure of VF
and
move from a medial to lateral direction.

28. • Indications
• Evaluation of laryngeal mucosa
• Mucosal vibration
• Vocal fold motion biomechanics
• Detecting and assessing pathology
• Planning effective phonomicrosurgery

29. • Advantage
• Office based procedure
• Painless
• Real-time information about nature of vibration
• Image to detect vocal pathology
• Permanent video record of examination
• Improves sensitivity of subtle laryngeal diagnoses

30. CONTACT ENDOSCOPY
• Simple, non - invasive technique
• In situ examination of
• Superficial cells of epithelium
• Mucosal blood vessels pattern
• Access microscopic structure of
entire mucosa
• Hamou (1979)
• Andrea et al. - evaluation larynx in 1995.

31. • Current contact microlaryngoscopes
• Diameters - 4 mm or 5.5 mm
• lengths - 23 cm and 18 cm
• Straight forward (O◦) and
forward oblique telescopes (30◦)
• Magnification - 1x, 60x, and 150x
• Require a high intensity xenon light source

32. • TECHNIQUE
• Sucking out secretion
• Endoscope - gently placed over suspicious site
• Viewing using 60X and 150X magnification
• Vascular patterns are studied without staining
• Then mucosa stained - 1% methylene blue soaked cotton pledgets
for 5 mins
• Stained area - visualized again
• Cell architecture
• Nuclei – dark blue structure
• Cytoplasm – light blue structure

33. • Advantage
• Non - invasive procedure
• Premalignant condition such as dysplasia detected earlier
• Avoids tissue damage and cellular architecture alteration
• Disadvantage
• Only evaluate most superficial cell layer of mucosal epithelium
• Inability to distinguish confidently between intraepithelial
neoplasia and invasive carcinoma

34. • Normal appearance
• Squamous cell at VF edge - polyhedric shape
• Nuclei - round, dark blue stain
• Cytoplasm - light blue stain
• Abnormal appearance
• Ciliated with squamous cell
1. Heavy smoker and GERD
• Ciliated epithelium of posterior commissure replace by squamous
epithelium

35. 2. Chronic laryngitis
• Epithelial pattern is homogenous, have large nuceli, Increase N:C
ratio
3. Keratosis
• Different stage of keratinization
4. Leukoplakia
• Cell - Heterogenicity
• Nuclei – different size, shape, and color
5. Carcinoma
• extreme heterogenicity of nuclear size, shape and staining
characteristic

36. • Image of blood vessels on normal VF
• Blood vessels are parallel to long axis of VF
• Bifurcations and anastomoses are few
• Image of blood vessels in early laryngeal
cancer

37. • Image of blood vessels in advanced
laryngeal cancer
• Leading to formation of vascular loops

38. • Image of cellular architecture of normal VF
• Cells : Homogenous with uniform size and
shape
• Nuclei : Uniform size and shape and evenly
stained
• N:C ratio : Uniform and less than 1
• Image of cellular architecture of squamous
carcinoma

39. NARROW BAND IMAGING (NBI)
• Non- invasive endoscopic technique - visualization of vascular
structure of mucosa
• Based on modification of standard white light –
• In which white light is transmitted through optical filter absorbing
all

40. • Principle
• Relies on depth of light penetration and absorption peak of Hb
• Use filtered light to visualize mucosal and submucosal
neoangiogenic vascular pattern

41. • NBI system consists
• Head or chip equipped videoendoscope
• Light source
• Camera unit
• Lighting unit with special filter
• Special image processor

42. • Narrow band blue light ( 390- 445nm )
• Imaging superficial capillaries of mucosal layer
• Is better absorbed by Hb
• Narrow band green light ( 530-550nm )
• Imaging thick vessels within mucosal layer
• Subepithelial vessels

43. • Blue color absorbed
by mucosal vessels
• Green color absorbed
by submucosal vessels
• NBI monitor representing
• Mucosal vessels – brown
colour
• Submucosal vessels – cyan
colour

44. • Vascular pattern associated with pathology includes
• Dotted – adenocarcinoma
• Tortous – squamous cell ca.
• Abruptly ending vessels – squamous cell ca.
• In diagnosis of primary laryngeal lesion
• Sensitivity – 89%
• Specificity – 93%

45. • Advantage
• Non invasive, done in opd basis
• Don’t require dyes
• Allow easy inspection of superficial vascular bed
• Early lesion < 1cm in diameter can be detected ( dysplasia, CIS )
• Disadvantage
• Lesion characterized by hyperkeratosis prevent visualization
• Can be limited in cases of stagnant saliva, sticky mucus

46. • Bilateral carcinoma of vocal folds in white-light (A) and NBI (B)
• Supraglottic spread of cancer is clearly visible on NBI image

47. • Larynx - left vocal cord dysplasia in white light (A) and NBI (B),
• Arrows point demarcates area of altered epithelium with presence
of brown dots

48. • Benign polyp of vocal cord in white-light (A) and NBI(B).
• Blood vessels run paralelly to the mucosal surface.