PHYSIOLOGY OF PHONATION

Dr. Ashwin Menon

DEFINITION

Rapid, periodic opening and closing of the glottis through separation and apposition of the vocal cords that, accompanied by breath under lung pressure, constitutes a source of vocal sound.

Other functions of Larynx

Protection of lower airways

Respiration

Fixation of Chest wall

Biomechanics of Phonation

Vocal Folds abduct on inspiration. Vocal Folds slightly adduct on

expiration. Full abduction in forceful inspiration

Larynx descends with Inspiration and Asends with expiration.

The requirements of normal phonation are as follows: Active respiratory support Adequate glottic closure Normal mucosal covering of the vocal cord

Adequate control of vocal fold length and tension.

Anatomy: Physical parts of the vocal system

Creating sound requires numerous muscles, bones and organs of the body

Three main anatomical aspects: Actuators: Lungs/diaphragm/intercostal

muscles; these organs deal with breathing/“air management”

Vibrator: larynx; this deals with the creation of pitch in the form of a sound wave

Resonators: Throat (pharynx), mouth/lips/teeth, nose; these deal with the modification of sound into varying accents

Respiration: Demonstration

Movement of diaphragm Movement of ribs/lungs

Phonation The larynx acts as a transducer during

phonation converting the aerodynamic forces generated by the lungs, diaphragm, chest and abdominal muscles into acoustic energy.

The consonants of speech can be associated with particular anatomical sites responsible for their generation i.e. 'p' and 'b' are labials, 't' and 'd' are dentals and 'm' and 'n' are nasals.

Initiation of Voice

Before phonation, vocal folds rapidly abduct to allow intake of air-Pre Phonatory inspiratory Phase (‘’Wyke’’)

Vocal folds adducted- Lat cricoarytenoid M

Pulmonic air forced between adducted Vocal Folds – vocal note

Repeated vibratory movt of the vocal folds – production of vocal note- Vocal fold oscillation

Amount of air pressure required to begin voicing – Phonation threshold pressure

THEORIES OF VOICE PRODUCTION

1. PUFF THEORY-Puff of air emitted through Glottis- vibratory action- Voice

2. NEUROCHRONAXIC THEORY-ROUL HUSSON(1950)Central impulses stimulate the RLN(beat by beat) leading to the active contraction of the thyroarytenoid M – vocal cord vibration.

This theory was not accepted as- Tracheostomy patients cannot phonate. Left RLN longer than the right.

3. CAVITY TONE THEORY – WILLISHe developed a series of resonating cavities with different shapes and lengths & coupled them to a vibrating reed source. He observed that the sound heard represented a particular vowel & it mainly depended on the length of the resonating tube independent of the reed tone and its frequency.

4. HARMONIC THEORY(OVERTONE/STEADY STATE THEORY)CHARLES WHEATSTONE

He noticed that the vowels heard were a combination of the reed tone and its harmonics. This modulated reed tone can be further modified at the supra laryngeal level giving rise to special sounds. But this theory fails to take into account the dampening effect.

5. MYO ELASTIC AERODYNAMIC THEORY-JOHANNES MULLER(1843)AERO- Air pressure & flowDYNAMIC- Movt & changeMYO- Muscular movtELASTIC- Ability to return to original state

6. COVER BODY THEORY

7. BODY SOURCE THEORY

8. SOURCE TRANSFER THEORY

VIBRATORY CYCLE1. ADDUCTION

2. AERODYNAMIC SEPARATION

3. RECOIL

Manifestation of a mucosal wave travelling from the inferior to the superior surface of each Vocal Fold.

Mucosal Wave

Also important component of vocal fold vibration/ voice production

Explained by Body-Cover model of vocal fold vibration Diff vibratory properties of vocal fold

layers Vertical phase differenceConditions that change density

relationships between cover & body result in decreased mucosal wave.

The Glottic Cycle The vocal folds alternately trap

and release air; each trap/release is one cycle of vibration. This cycle is often referred to as the glottic cycle, and it is divided into phases:

I. opening phaseII. open phaseIII. closing phaseIV. closed phase

During the closed phase, the air pressure builds up below the vocal folds. When the glottis opens, the air explodes through the vocal folds, and that's the beginning of the sound wave. The strength of that explosion determines the loudness of the sound coming directly from the larynx.

First, the laryngeal muscles position the vocal cords in various degrees of adduction and place them under the appropriate longitudinal tension.

Next, muscular and passive forces of exhalation cause the subglottic air pressure to increase.

When this subglottic pressure reaches a point where it exceeds muscular opposition, the glottic chink is forced to open.

When the vocal cords start opening from complete closure, they open in a posterior to anterior direction with the posterior portion of the glottis opening first, reaching maximum excursion first, and recontacting each other at the end of the vibratory cycle prior to the anterior portion of the cords.

After release of the puff of air there is a reduction of sub glottic pressure, and the vocal cords approximate each other again (myo elastic forces of the vocal cords have exceeded the aerodynamic forces).

The myo elastic forces are enhanced because air current flowing through a narrow channel exerts a negative pressure on the channel walls; This is the basis of Bernoulli's Principle.

The vocal cords are thus sucked back together in an adducted state until the sub glottic air pressure can overcome the myo elastic forces of the re approximated cords, and the cycle is then repeated.

FEATURES OF SOUND:1. PITCH

It is the number of vibrations of vocal cords per second

Depends on:a. Length of VC.

b. Mass of VC.

c. Tension of VC.

In general, men's vocal folds can vibrate from 90 - 500 Hz, and they average about 115 Hz in conversation.

Women's vocal folds can vibrate from 150 -1000 Hz, and they average about 200 Hz in conversation.

PITCH = T L M

Vocal folds vibrate faster as they're pulled longer, thinner, and more taut and vibrate more slowly when they're shorter, thicker, and floppier.

The cricothyroid muscle and thyroarytenoid muscle coordinate with each other to create different pitches.

2. VOLUME(INTENSITY) & LENGTH(DURATION)

Depends on the air pressure created which is in turn dependent on the lung capacities.

3. QUALITY(TIMBER)

Depends on the overtones added by the resonators and articulators.

Vocal Register differences in mode of vibration of

vocal foldsRegister may include

Equivalent terms Vocal folds F0 range(Hz)

Loft registerHighest vocal freq

Falsetto Thin, tense, lengthened.Minimal vibration

275-1100

Modal registerUsual freq employed in speaking & singing

Chest, head, middle, heavy voice

Complete adduction

100-300

Pulse registerLowest range of vocal freq

Vocal fry, glottal fry, creaky voice

Long closed phase

20-60

Vocal Disorders Organic, Functional & Psychogenic. Puberphonia- Maintenance of the

childhood pitch despite having passed through puberty

Spasmodic Dysphonia Stuttering Phonasthenia Bogart-Bacall syndrome

Vocal Injury It is fairly easy to injure the vocal cords!

Forceful singing, yelling, screaming, loud talking can cause the vocal cords to hit very hard and result in injury to the cords - vocal abuse

Excessive amounts of phonation can also lead to injury - vocal overuse

Nodules, polyps, laryngitis and hemorrhage of the cords are possible effects of such vocal abuse

Smoking also has dramatic effects on the larynx!

Nodules

Nodules (also called “nodes”): A common injury that is essentially a small growth found on both of the cords (nodules are much like a callus on the hand or foot); Nodules keep the cords from fully closing, resulting in a harsh/breathy voice

Polyps Polyps are like nodules in that they

are also a growth on the cords that keep the cords from closing, but are more like a soft lesion than a hard callus

Polyps may be on either just one cord or both (typically on just one side); both abusive phonation and smoking are common reasons for polyps

Hemorrhage

A hemorrhage is where a blood vessel rupture due to excessive pressure

Laryngitis Laryngitis is the inflammation of

the vocal cords

It may be the result of reactions to allergies, bacterial or fungal infections, or the result of vocal overuse

With laryngitis, the vocal cords often swell too much to correctly close, resulting in the lack of phonation

Acid Reflux as irritant Reflux can cause significant irritation,

burning or swelling on vocal cords/larynx; Two types:

“GERD”: Gastroesophageal reflux disorder– is when acid backflows into esophagus Symptoms: Heartburn, regurgitation;

occurs while laying down

“LPR”: Laryngopharyngeal reflux– is when acid backflows into larynx/pharynx Symptoms: Too much mucous in throat,

need to clear throat often, sour taste in mouth, hoarse voice, feeling of a “lump” in the throat

CANCER

VIDEO STROBOSCOPY Invented by JAN G SVEC.

It has evolved as the most practical and useful technique for the clinical evaluation of the visco-elastic properties of the phonatory mucosa.

Done with topical anaesthesia.

Essential diagnostic procedure for the evaluation of laryngeal mucosa, vocal fold motion biomechanics & mucosal vibration.

It uses a synchronized, flashing light passed through a flexible or rigid telescope.

Flashes of light from the stroboscope are synchronized to the vocal fold vibration at a slightly slower speed, allowing the examiner to observe vocal fold vibration during sound production in what appears to be slow motion.

VIDEO STROBOSCOPY OF VOCAL CORDS

THANK YOU!!!