Physiology of Larynx PDF

Physiology of Phonation JP Louboutin 30/9/2024 1. Nonspeech laryngeal function 2. Laryngeal function for speech 3. Review of basic acoustics 4. Intruments for voicing 5. Bernouilli effect 6. Types of sounds 7. How to measure phonation: frequencies? 8. Theories of vocal fold vi...

Physiology of Phonation JP Louboutin 30/9/2024 1. Nonspeech laryngeal function 2. Laryngeal function for speech 3. Review of basic acoustics 4. Intruments for voicing 5. Bernouilli effect 6. Types of sounds 7. How to measure phonation: frequencies? 8. Theories of vocal fold vibration 9. Pitch and intensity change 10. Changes in vocal intensity  Nonspeech laryngeal function Respiration. Abduction of vocal folds. During normal respiration, vocal folds abducted to provide a width of about 8 mm in adult. During forced respiration, the respiratory tract is open as widely as possible (about 16 mm) Protection of the airway. Most important function of the larynx as entry of foreign bodies is life threatening. Epiglotti. Coughing. Response by the tissues of the respiratory passageway to an irritant or foreign objec (adduction of vocal folds). Abdominal fixation. Process of capturing air within the thorax to provide the muscles with a structure on which to pull or push (adduction of vocal folds) Fiberendoscopic view of superior larynx withFiberendoscopic view of superior larynx with abducted vocal folds adducted vocal folds Laryngeal function for speech QUICK REVIEW OF BASIC ACOUSTICS Sound: audible disturbance in air Vibrating body disturbs air Simple harmonic motion: vibratory motion that has one period of vibration Frequency: number of cycles per second (Hertz, or Hz) Period: time taken to complete one cycle (in milliseconds, ms, typically) Cycle of vibration: moving from one point in the vibratory pattern to the same point again FREQUENCY OF VIBRATION OF A BODY Frequency is determined largely by mass and tension Mass: Increase mass, decrease frequency Tension: Increase tension, increase frequency  ELASTICITY Elasticity: the property of matter that causes it to return to original shape after being deformed Stiffness: strength of elastic forces Inertia: property of a body that tends to oppose any change in velocity of the body (i.e. opposes acceleration)  A B C D E F A guitar string illustrates oscillation. A: The string is at rest. B: A finger forces the string into displacement. C: The string is released and its elastic elements cause it to return toward the rest position. D: The string overshoots the rest position because of its inertia. E: The string reaches the extreme point of its excursion past the rest position. F: Elastic forces within the string cause the string to return toward  Amplitude and intensity. Intensity of sound: related to amplitude of waveform. Amplitude of vibration correlates with sound pressure. Sound pressure: correlate of voltage, so measurement of the output of a microphone can be used to calculate intensity of sound. Decibel (dB): ratio of two sound pressures or powers expressed logarithmically  Periodic motion of a vibrating body graphically recorded he graph was a microphone output being recorded, the y-axis would be volts, reflecting the ree to which the microphone receiver had moved when we spoke into it. Sound waves consist o illations of air molecules called compressions and rarefactions. When the vibration is pushing ard the microphone, it is considered to be a compression, and it is a rarefaction when it is ving away from the microphone  Instruments for voicing nstrumentation for voicing includes tools for processing and analyzing the audio signal requency, intensity) and the physiology of the vocal folds ntensity is measured using the sound level meter, and there are many tools allowing this in ustained phonation or running speech Vocal jitter (perturbation) quantifies cycle-by-cycle differences in vibration of the vocal folds nd vocal shimmer examines cycle-by-cycle differences in intensity Phonogram: means of showing interaction between intensity and frequency for an individual Airflow is sensed using a pneumotachograph typically placed within a face mask Subglottal pressure measured by hypodermic needle through the cricothyroid membrane r estimated by measuring intraoral pressure when the vocal folds are open Nasoendoscopy involves insertion of a fiber endoscope intranasally to provide an image of the ocal folds and laryngeal structures in real time Electroglottograph (EGG) uses a pair of electrodes affixed to the surface of the neck to provide graphic trace that corresponds to the degree of vocal fold contact Nasoendoscopy Electroglottograph (EGG)  BERNOUILLI EFFECT Bernoulli's principle is a key concept in fluid dynamics that relates pressure, speed and eight. Bernoulli's principle states that an increase in the speed of a parcel of fluid occurs multaneously with a decrease in either the pressure or the height above a datum The Bernoulli effect can be illustrated with a Venturi tube. In the convergent zone, liquid ccelerates, and the velocity at the cylindrical throat section is higher The pressure drops as a result of velocity increase according to the Bernouilli equation A fine tube connects the chamber to the atmosphere. Air is automatically sucked into the liquid ream and is well broken into fine bubbles by the highly-turbulent shear flow Liquid flow acceleration can also be realized by mechanical agitation and liquid swirl motion A flow of air through a venture meter. The kinetic energy increases at the expense of the fluid, as shown by the difference in height of the two columns of water Vocal folds from above Coronal section of larynx showing constriction in laryngeal space caused by the vocal folds honation or voicing: product of vibrating vocal folds within the larynx he vocal folds vibrate as air flows in larynx; the Bernouilli phenomenon and tissue elasticity he aintain phonation ernouilli effect states that given a constant volume flow of air or fluid, at a point of constriction ere will be a decrease in pressure perpendicular to the flow and an increase in velocity of e flow he interaction of subglottal pressure, tissue elasticity, and constriction within the airflow used by the vocal folds produces sustained phonation as long as pressure, flow and vocal d approximation are maintained. One cycle of vocal fold vibration as seen through a frontal section. A. Air pressure beneath the vocal folds arises from respiratory flow B. Air pressure causes the vocal folds to separate inferiorly C. The superior aspect of the vocal folds begins to open D. The vocal folds are blown open, the flow between the folds increases, and pressure at the folds decreases E. Decreased pressure and the elastic quality of vocal folds causes the folds to move back toward midline F. The vocal folds make contact inferiorly G. The cycle of vibration is completed  RESONANCE The tendency for a body to vibrate at a specific frequency, based upon physical characteristics of the vibrating body. e.g., Tuning fork, swing INPUT-OUTPUT DIAGRAM TUNING CURVE  INPUT-OUTPUT DIAGRAM Takes more energy to drive swing off its characteristic or resonating frequency (fc) Vibrating body has a natural frequency or natural resonance A body will vibrate at its resonant frequency when it is excited To change resonant frequency, alter length, tension, mass  SOUND 4 basic types: Simple periodic: sound characterized by a single frequency of vibration Complex periodic: sound characterized by more than one frequency of vibration Aperiodic: sound without an identifiable frequency of vibration Mixed periodic/aperiodic: sound with both periodic and aperiodic elements HOW TO MEASURE PHONATION: FREQUENCY Fundamental frequency (f0): Lowest frequency of the complex phonatory source What are changes with age and sex? What are maximum sustained durations? What is the optimal fundamental frequency? What is the habitual fundamental frequency? What is the range of phonation? RATE OF VIBRATION OF VOCAL FOLDS Rate of vibration = fundamental frequency (f0) ~120 Hz for males ~220 Hz for females ~250 Hz for children  HARMONIC SERIES Whole number multiples of the fundamental f0=100 2f0=200 3f0=300 Pitch = psychological correlate of frequency Pitch is ~= f0 in simple harmonic series  HOW LONG CAN YOU SUSTAIN A VOWEL? Vowel Duration by Age 70 Females Males stabilizes Begin 60 decline Duration (seconds) 50 40 30 From Kent, 1994. Reference 20 Manual for Communication 10 Sciences & Disorders. Austin, Pro-Ed. (maximum phonation 0 duration as a function of age 1- 5- 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 4 9 - - - - - - - - - - - - - - - 14 19 24 29 34 39 44 49 54 59 64 69 74 79 84  OPTIMAL F0 The average fundamental frequency at which vocal folds vibrate most efficiently (resonant frequency)  HABITUAL F0 The average fundamental frequency at which an individual’s vocal folds vibrate during normal conversational speech. An octave: interval between one musical pitch and another with double or half its frequency. For example, if one note has a frequency of 440 Hz, the note one octave above is at 880 Hz, and the note one octave below is at 220 Hz. The ratio of frequencies of two notes an octave apart is therefore 2:1. Further octaves of a note occur at 2n times the frequency of that note (where n is an integer), such as 2, 4, 8, 16, etc. and the reciprocal of that series. For example, 55 Hz and 440 Hz are one and two octaves away from 110 Hz because they are 1⁄2 (or 2-1) and 4 (or22) times the frequency, respectively. The number of octaves between two frequencies is given by the formula:  RANGE OF F0 The difference between the maximum fundamental frequency of vibration of modal phonation and the minimal fundamental frequency of vibration (hi-low) About two octaves About.25 octave below optimal f0 About 1.75 octave above f0 So male = about 90 to 360 Hz Female = 190 to 760 Hz DIFFERENTIAL MODES OF VOCAL FOLD VIBRATION Modal phonation Falsetto Glottal fry Vibrato (Whisper) MODAL PHONATION (OR CHEST REGISTER) Phonatory pattern used during normal phonation The pattern used most frequently or modal pattern  VIBRATORY PATTERNS OF VOCAL FOLDS Two simultaneous patterns of vibration make up modal phonation Transverse dimension: antero-posterior dimension Folds open posterior to anterior Close anterior to posterior Vertical dimension Folds open inferior to superior Folds close inferior to superior This is the most consistent mode  FALSETTO Falsetto: Higher range: 350-600 Hz or so Mode shifts: vocal folds become thin & elongated Tense margins & bow shaped Posterior portion is damped, so vibrating margin is shortened Only margins vibrate In falsetto, the extreme membranous edges (i.e., the edges furthest away from the middle of the gap between the folds) appear to be the only parts vibrating Overlap in frequency with modal vibratory pattern  GLOTTAL FRY Lower pitch range Quiet phonation Frequency 30-80 Hz Closed phase = 90% of vibratory cycle Opening & closing = 10% total Syncopated vibration: open and close twice, then closed long time Extremely low subglottal pressure (2 cm H20) Oscillographic comparison of glottal fry (top) and modal phonation (bottom) for the vowel /a/ A VOCAL MODIFICATION: VIBRATO Rapid, small changes in pitch Musical "color“ A “NON-MODE” OF VIBRATION: WHISPER Non-phonatory sound production Non-vibrating folds Slightly abducted and toed in Small chink Turbulence as air passes through constriction Uneconomical Abusive? Tension of mechanism! THEORIES OF VOCAL FOLD VIBRATION MYOELASTIC-AERODYNAMIC THEORY Air stream passes between folds Vibrate as result of elastic quality of tissue interacting with aerodynamic principles embodied in Bernoulli principle Frequency of vibration vary according to tension, mass, elasticity of the tissue Essentially a single mass and spring system  MUCOVISCOELASTIC AERODYNAMIC THEORY: TIETZE Incorporates myoelastic-aerodynamic theory Looks at vocal folds as series of loosely connected masses Acknowledges the loose linkage of the epithelial layer and vocal ligament Accounts for the undulation which results in the phase difference seen during vibration (inferior-superior vibration) NEUROCHRONAXIC THEORY OF VOCAL FOLD VIBRATION Each cycle of vibration is initiated by a neural impulse For 500Hz there will be 500 neural impulses per second Is not the case for humans (proof is that we can’t vibrate our vocal folds without air passing through larynx) IS how cats purr, however! PITCH AND INTENSITY CHANGE  HOW DO WE MAKE THE VARIOUS LARYNGEAL ADJUSTMENTS OF SPEECH? Pitch change Pitch is the perceptual correlate of frequency Intensity change Loudness is the perceptual correlate of intensity  PITCH CHANGE MECHANISM First a necessary concept: Medial compression: force exerted toward the midline which tends to keep vocal folds (VF) approximated Medial compression is a product of the muscles of adduction Lateral cricoarytenoid Oblique and transverse arytenoids More medial compression requires more air pressure to blow VF apart HOW DO WE CHANGE PITCH? As tension increases, pitch increases As mass increases, pitch decreases Muscles that tense will raise pitch Muscles that relax will lower pitch Muscles that decrease length will lower pitch Muscles that increase length raise pitch  MECHANISM FOR INCREASING TENSION Primary mechanism: Cricothyroid pars recta Thyroarytenoid (vocalis) In addition Posterior cricoarytenoid anchors Cricothyroid puts vocal folds into gross posture Thyroarytenoid does fine tuning of tension Geniohyoid elevates larynx WHAT DO FOLDS LOOK LIKE WITH HIGH PITCH? Longer Thin Stiff Rigid  MECHANISM FOR LOWERING PITCH Increase mass per unit length or decrease tension Thyromuscularis pulls thyroid and cricoid together; relaxes vocalis Maybe inferior pharyngeal constrictor pushes on thyroid at notch? Compresses thyroid in anterior-posterior dimension? RESPIRATORY CHANGES DURING PITCH CHANGE To increase f0, increase tension and medial compression necessary Increasing tension requires increased subglottal pressure They co-occur as result of overcoming tension Increased subglottal pressure doesn't increase pitch but is necessary to sustain increased pitch  HOW DO WE CHANGE VOCAL INTENSITY? Two mechanisms acting on: Subglottal pressure Closed phase of vibration  SUBGLOTTAL PRESSURE To increase sound pressure we must increase force of medial compression Increase medial compression via adduction Lateral cricoarytenoid Oblique and transverse arytenoid Thyroarytenoid (thyrovocalis) Cricothyroid (to provide tensing counter active force) Requires greater subglottal effort to overcome Are blown apart more vigorously As subglottal pressure increases, vocal intensity increases  CLOSED PHASE OF VIBRATION CHANGES Opening Closing Closed Conversational Intensity 50% 37% 13% +5dB increase 33% 33% 33% As vocal intensity increases opening phase drops to 33% closing phase drops to 33% closed phase increases to 33% For some people, they will not have increased air flow others will Generally, best ability to change vocal intensity in mid-range of frequency  FLETCHER’S WORK Openin g Close d Closin g Red = High Intensity Blue = Low Intensity  ffect of vocal intensity as shown through electroglottographic trace: The electroglottograph measures impendance across the vocal folds, and the peak represents the closed phase of the lottal cycle. A. Conversational-level sustained vowel. B. High-level sustained vowel  CLINICAL UTILITY Range of phonation Maximum phonation time Vocal jitter Breathiness  RANGE OF PHONATION Normal range is about two octaves Octave is a doubling of frequency Example: my lowest f0 is 133 Hz, one octave up from that is 266HZ Two octaves up (my range) is 532 Hz Range often reduces as result of vocal abuse, pathology Damage to superior laryngeal branch of X vagus  MAXIMUM PHONATION TIME Maximum amount of time a person can systain phonation of “ah” Measure of air costs Vocal nodules, growths cause air wastage Results in shorter duration of phonation About 15 to 25 seconds in adult females About 25 to 36 seconds in adult males Age (yrs.) Female Male 6 11sec 11sec 7 11 12 8 15 13 9 9 11 10 9 10 11 12 13 12 14 17 MAXIMUM PHONATION TIME FROM KENT 30 28 27.52 25 24.48 22.96 22 22 22 21 21 21.18 20 20 20 Maximum duration in seconds 18 17 15 15 14 10 10 10 8 5 0 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 u lt s -7 0 -8 0 -8 9 1 1 1 ad 6 7 8 g un Yo Age in Years  VOCAL JITTER (PERTURBATION) Cycle by cycle variability in vocal fold vibration Expressed as percentage variability relative to mean period Greater jitter = rough voice > 1% = perception of roughness Vocal jitter is sensitive to pathology, health status, etc.  BREATHINESS Indication of inefficient phonation Adds noise to phonation THANK YOU!