Physiology of phonation by Dr. Farhat Khan

the ppt includes the anatomy of larynx, the physiology of sound production and pathology of vocal cords explaining the myoelastic aerodynamic theory and bernoulli effect in phonation

1. PHYSIOLOGY OF PHONATION Presented by: Dr. Farhat Khan M.S (ENT)

2. Introduction Definition Relevent anatomy Theories of phonation Mechanism of voice production Properties of phonation Changes in voice

3. Portrays our thoughts, emotions , joys and fears Signatures of the individuals Ancient Greeks thought that the voice actually originated in the heart. Human speech requires coordinated interaction of the mouth, pharynx, larynx, lungs, diaphragm, and abdominal and neck muscles. HUMAN VOICE

4. Phonation can be defined as laryngeal motor behaviour used for speech production ,which involves a highly specialised coordination of laryngeal and respiratory neuromuscular control. It is the process of sound production by means of the release of air puffs through glottal opening and closing as a result of the interaction among tissue characteristics and muscular and aerodynamic forces. Definition

5. Phonation, or the production of voice, involves a power source (generator), oscillator( phonator ), and resonance chamber and articulator each with different anatomical parts and specialized roles. Together, these three subsystems produce sound perceived as voice.

6. Articulator Resonator Phonator Generator

7. Laryngeal Anatomy and Structure Location: C3 to C6 Connects pharynx to trachea Cartilages Membranes and ligaments Muscles Nerve supply

8. Cartilages : 9 [3 paired, 3 unpaired]

9. Muscles: 7 Cricothyroid Thyro arytenoid Inter arytenoid Lateral cricoarytenoid Posterior cricoarytenoid Oblique arytenoid Vocalis

10. Intrinsic muscles : act on vocal cord or laryngeal inlet Vocal cord: Abductors- PCA Adductors- LCA,IA,TA Tensors – CT,Vocalis Laryngeal inlet: 1.Elevators Primary Secondary Stylopharyngeous Mylohoid Salphingopharyngeous Stylohyoid Palatopharyngeous Geniohyoid Thyrohyoid Digastric 2.Depressors Stenohyoid Omohyoid sternothyroid

11. Musculature of the Vocal Fold The intrinsic laryngeal muscles- control the position and shape of the folds along with the elasticity and viscosity of each layer. The fibers of the thyroarytenoid muscle run parallel to the vocal ligament. The part of the muscle that borders the vocal ligament is called the vocalis muscle. Contraction of the thyroarytenoid muscle lowers, shortens, adducts, and thickens the vocal fold, bringing the arytenoid and thyroid cartilages closer.

12. When the thyroarytenoid muscle is activated, the length and tension of the vocal ligament are decreased, lowering the pitch of the voice. The vocalis muscle can provide fine control of the tension in the vocal ligaments enabling rapid variation in the pitch. The posterior cricoarytenoid muscle abducts, elevates, elongates, and thins the vocal fold by rocking the arytenoid cartilage posterolaterally . The lateral cricoarytenoid muscle adducts, lowers, elongates, and thins the vocal fold, making the edge of the vocal fold sharp while passively stiffening all layers.

13. The interarytenoid muscle serves to adduct the cartilaginous portion of the vocal folds. The extrinsic muscles of the larynx, mainly the strap muscles, serve an important function of preserving the position of the larynx in the neck.

14. Structure of the Vocal Fold Edge The vocal folds are two infoldings of mucous membrane stretched horizontally across the larynx. The most important aspect of voice production is vibration of the vocal folds that converts aerodynamic energy into acoustic energy. The cross-section of the vocal fold reveals a five-layered structure, with each layer having a different mechanical property. The outer four layers are controlled passively and the innermost layer is controlled both actively and passively.

15. Functionally, the vocal fold acts as three separate layers - The cover (epithelium and Reinke space), The transition (intermediate and deep layers of the lamina propria ) and The body (vocal is muscle ).

16. Nerve supply: All muscles > adductors; except PCA > abductor All muscles are supplied by recurrent laryngeal nerve ; except cricothyroid (strongest adductor) > superior laryngeal nerve

17. Position of vocal cord DISTANCE(mm) NORMAL DISEASE MEDIAN phonation RLNP PARAMEDIAN 1 whisper RLNP INTERMEDIATE (cadaveric position) 3 xxxxx BOTH N PALSY GENTLE ABDUCTION 7 Quite respiration SLNP FULL ADDUCTION 9 Deep respiration SLNP

18. Management U/L RLNP P Hoarseness wait and watch B/L RLNP P P Severe dyspnoea tracheostomy U/L SLNP abd Hoarseness No aspiration No dyspnoea Wait and watch B/L SLNP abd abd Aspiration Aphoneoa No dyspnoea Epiglotoplasty tracheostomy

19. HISTORICAL ASPECT OF PHONATION In 1950, Husson presented the neurochronaxic hypothesis , which held that glottic vibrations were caused by rhythmic impulses in the nerves to the larynx, synchronous with the frequency of the sound produced, so that each vibratory cycle was caused by a separate neural impulse—a physiologically impossible hypothesis.

20. HISTORICAL ASPECT OF PHONATION In the 1950s, van den Berg used high-speed motion pictures to document the motion of the vocal folds during vibration and subsequently reported his theory of the mechanism of phonation; now widely accepted, the myoelastic -aerodynamic theory holds that the interaction of aerodynamic forces and the mechanical properties of the laryngeal tissues are responsible for inducing vocal fold vibration and generating vocal sound.

21. Normal phonation requires that five conditions be satisfied; 1. Adequate breath support 2. Approximation of vocal folds 3. Favorable vibratory properties 4. Favorable vocal fold shape 5. Control of length and tension

22. The process of phonation begins with the inhalation of air, and then glottic closure positions of the vocal folds near the midline. Explanation of phonation is that exhalation causes subglottic pressure to increase until the vocal folds are displaced laterally, which produces a sudden decrease in subglottic pressure. The forces that contribute to the return of the vocal folds to the midline include this pressure decrease, elastic forces in the vocal fold, and the Bernoulli effect on airflow. When the vocal folds return to the midline, pressure in the trachea builds again, and the cycle is repeated. Vocal fold structure determines whether the resulting vibration is periodic or chaotic.

23. The “body-cover” concept of phonation is that the vibration of the mucosa does not correspond directly to that of the rest of the vocal fold. Instead, the “body” of the vocal fold is relatively static, whereas the wave is propagated in the mucosal “cover.” This mucosal wave begins on the inferomedial aspect of the vocal fold and moves rostrally .

24. Helmholtz (1863) showed us that phonation was the product of puffs of air released through the glottis. Voice is produced by a steady flow of air from the lungs, segmented at the laryngeal level into a series of air puffs at a fundamental frequency that generates higher harmonics in the cavities of the upper airway. Which frequencies will be produced with a minimum attenuation will be determined by the configuration of the supra-laryngeal cavities. Acoustic energy concentrations due to cavity resonation are called formant frequencies.

25. Myoelastic -Aerodynamic Theory (Van Den Berg, 1958) Muscular activity rotates and rocks the arytenoid cartilages so that their vocal processes come together in the midline, thus positioning the vocal folds close together or in actual contact. Air pressure increases below the glottis until folds forced apart Air travels faster through the glottis when it is narrow. This causes a local drop in air pressure ( Bernoulli effect ) which causes the folds to be sucked towards each other. The Bernoulli effect, together with the elastic recoil force exerted by the displaced vocal folds, causes complete glottal closure again. The process begins again at step 2.

26. Physics of the Myoelastic -aerodynamic theory of phonation is given by Lieberman (1968) Two forces act on the vocal folds: Aerodynamic-aerostatic forces displacing the vocal folds from their adducted position in preparation for phonation and Tissue forces that act to restore the vocal folds to their adducted position.

27. Bernoulli Effect : Daniel bernoulli , Swiss mathematician and physicist (1700-1782) Inverse relationship Increase in air flow results in air pressure decrease

28. Timcke et al . (1958, 1959) pioneered the frame-by-frame analysis of ultraspeed photographs of the vocal folds during phonation showing the opening and closing of the glottis during each vibratory cycle. In a normal vibratory cycle, glottal width is displayed on the vertical axis, and duration of the cycle is shown on the horizontal axis. Each cycle is divided into an opening, a closing, and an approximation phase. In a normal voice, the vocal folds abduct at a higher rate of speed than they adduct. An equation expressing the ratio of abductor to adductor duration is called the speed quotient (S.Q.):

29. In normal voices, the S.Q. is always less than 1.0, but as vocal intensity increases, the S.Q. increases (i.e., duration of the opening phase is increased). A second measure of vocal fold behavior during the glottic cycle is the ratio of the duration of the open period of the vocal folds to the total period of the cycle, called the open quotient (O.Q.): In normal voice, the O.Q. ranges from 0.6 to 0.8 and increases with vocal intensity.

30. Importance of these measures and the profile of the glottal wave shape is they change with changes in pitch and loudness and when the voice becomes dysphonic. By knowing the configuration of the normal shape and its variants related to pitch, loudness, and various voice qualities, we can use the wave shape to tell us something about how voice is being produced. For example, when the closed phase is long, we assume hyperfunction , and when there is no closed phase, we assume inadequate closure as seen in closed head injuries and breathy asthenic phonation.

31. Vibratory Function of Vocal Fold Mucosa The body-cover theory of vocal fold vibration was introduced by Hirano in 1974. He was one of the first to recognize that the morphologic structure of the vocal folds was central to normal vibration patterns. The theory assumes that the differences in histologic structure and contractile properties result in a five-layered histologic structure that vibrates as a two-layered biomechanical structure. The body, thyroarytenoid, is active, whereas the cover, epithelium, and lamina propria is passive.

32. The cover - pliable, elastic, and noncontractile The body - stiff and has active contractile properties. The body is able to adjust concentration and stiffness of mass. The overall tension is dependent upon the coupling of the cover to the contractile muscular body. The cover is important in its wave-like movement during phonation. Loss of cover movement or mucosal wave is detrimental to vocal quality. During phonation produced at normal pitch and loudness, the body is stiff and the cover loose.

33. The difference in stiffness between the two layers facilitates the mucosal wave. If any of the tissue cover is stiff because of changes in the epithelium, collagen, or elastin , the mucosal wave becomes reduced or eliminated. Conversely, in cases of paralysis when the muscle no longer contracts, the cover movement is aberrant because there is not the underlying stiffness so that the body and cover vibrate as one passive unit. During normal changes in pitch and loudness, the laryngeal muscles act on the passive tissue covering to produce differences in shape and tension.

34. As example, during high pitch the elongated vocal folds stretch the cover leaving only a small margin of tissue free to oscillate, whereas the converse is true for low pitch. These differences in vibratory pattern were primarily determined from high-speed photography done by von Leden and Moore in the 1940s and later by Hirano.

35. Properties of Phonation Sound can be described in terms of the physical properties of its pressure waveform Amplitude Frequency Pitch

36. Amplitude Amplitude of the pressure wave is perceived as loudness or sound intensity The amplitude is largely determined by the force of the transglottal airflow. “Shimmer” or amplitude perturbation

37. Frequency The frequency of the glottal signal is a result of the number of vibratory cycles / sec ( measured in Hz) Function of Vocal fold length Elasticity Tension Mass

38. Pitch Frequency, intensity and spectral properties of sound interact in very complex ways to lead to a given pitch perception. “Jitter” or pitch perturbation It is generally accepted that there are three pitch registers Loft (or falsetto) register Modal (or middle) register Pulse (or chest) register

39. Modal or Middle Register Pattern of phonation used in daily conversation Complete glottal closure occurs Results in the majority of the mid frequency range voice Vocal fold mucosa vibrates independently of the vocalis

40. Loft or Falsetto Register A singing technique that produces sounds that are pitched higher than the singer's normal range Vocal folds are lengthened and become extremely thin Only the edges of the vocal cord vibrate, not the entire vocal cord It is a very common technique in soul music, and has also been made popular in heavy metal Thin, high- pitched voice Voice of mickey mouse is another example of falsetto

41. Pulse or Chest register Also known as strohbass (straw bass) Crackly, popcorn quality of voice Low in pitch, sounds rough Vocal folds vibrate between 30 and 90 hz Frying pan sound of eggs frying (also called glottal fry) Low subglottal pressure Tension of the vocalis is significantly reduced relative to modal vibration, so that the vibrating margin is flaccid and thick The lateral portion of folds is tensed creating thick folds

42. Whistle Register Register above falsetto (flageolet register ) is the highest register of the human voice Up to 2500 Hz in females Product of turbulence on the edge of the vocal fold Not considered a mode of vibration as product of turbulence

43. Attacks Process of bringing vocal folds together to begin phonation, requires muscular action There are three kinds of attacks (or beginning of the each voiced sound) Simultaneous - attack-coordinate adduction and onset of respiration so that they occur simultaneously (i.e. say the word “zany”- you start the flow of air before voicing) Glottal- adduction of the vocal folds occurs prior to the airflow, much like a cough (i.e. bring vocal folds together like you are going to cough- and then say /a/, or say “okay, I want the car.” Breathy- starting significant airflow before adducting the vocal folds (i.e. running speech “Harry is my friend.” the air flow past your lips

44. Termination Process of fold retraction (abduction)

45. Changes in voice

46. Changes in voice Pathological Processes involved in voice disorders Generation of air pressure Glottic closure Vocal fold vibration Voice loudness Voice pitch

47. Generating Air Pressure Pulmonary disease Asthma Subglottic stenosis Paresis of muscles Symptoms Shortness of breath Weak voice

48. Glottic Closure Nerve Paresis Unilateral Recurrent Laryngeal Nerve Bilateral Recurrent Laryngeal Nerve Unilateral Superior Laryngeal Nerve Bilateral Superior Laryngeal Nerve Combined Recurrent & Superior laryngeal Nerve Symptoms Hoarseness Effortful phonation Vocal fatigue

49. Vocal Fold Vibration Vocal fold scar or vocal fold lesions Cysts, nodules, polyps ,papilloma ,vocal fold granuloma Swelling and inflammation (reflux laryngitis, viral laryngitis) Reinke’s edema Paresis, haemorrhage , vascular ectasis Symptoms Hoarseness Effortful phonation Weak voice Speaking voice lower than usual “glottal fry”

50. Voice Loudness Vocal fold scar Paresis Vocal fold lesions: cysts, nodules, polyps, papilloma Vocal fold granuloma Swelling and inflammation (reflux laryngitis, viral laryngitis) Symptoms Unable to project voice Weak voice Voice breaks

51. Voice Pitch SLN paresis Vocal fold scar Reinke’s edema Vocal fold lesions Symptoms Unable to hit high notes Voice breaks

52. Dysphonia Plica Ventricularis Voice is produced by ventricular folds (false cords) Seen in Mimicry Voice is rough, low pitch and unpleasant May be secondary to impaired function of the true vocal cord such as paralysis, fixation, surgical excision or tumors Ventricular bands in these situations try to compensate or assume phonatory function of true vocal cords

53. Androphonia Male like voice in female Low pitch Treatment:type IV thyroplasty

54. Mogiphonia Abnormal voice in front of public Traetment : speech therapy

55. Puberphonia High pitch voice at puberty This condition is only seen in emotionally dependent boys. Non organic cause (functional cause) Clinical diagnosis: GUTZMANN TEST – push thyroid backward and downward

56. Functional aphonia Seen in young females No voice with normal cough sound Larynx – normal Treatment : psychotherapy

57. Non Vocalized Sounds Whisper Whistle

58. REFERENCES Scott brown Thieme book of laryngology Ballenger Kenhub Dhingra

59. THANK YOU