Notes

Outline

How Far Can The Vocal Folds Travel? In Honor of Willard R. Zemlin Ingo R. Titze, Ph.D. Distinguished Professor of Speech Science and Voice The University of Iowa Director National Center for Voice and Speech

20-25%  of the U.S. workforce use voice as a primary tool of trade Teachers Counselors Telephone workers Agents Receptionists Lawyers Ministers, etc.

How do the vocal folds travel? Up and down, and sideways In loops - circles, ellipses, figure 8s

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How far can your vocal folds travel? They are stuck; can’t go anywhere Until they are “pooped” out As far as they want to – no limit With adequate rest, several km a day

Limitations –Overexposure to Tissue Vibration, Resulting in Nodules Polyps Chronic edema Vascular hemorrhages Vocal fatigue

Voice problems in teachers: The primary concern

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Ear-Larynx Two unique organs where tissue is vibrated at high frequencies

Comparative tissue vibration amplitudes Hearing:    low amplitudes (~ 0.001 mm) Voicing:    high amplitudes (~ 1 mm)

Protection of the sounding mechanism (the voice) is as vital as protection of the hearing mechanism (the ear)

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Vibration Dose Depends on Amplitude of vibration Frequency of vibration Duration of vibration

Vibration dose criteria derived from industrial tool use (Griffin,1990) For hand-transmitted vibration Continuous exposure Based on “white finger” and “numbness of hands” responses

Safety limits for hand-transmitted vibration (Griffin, 1990)

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Maximum Vocal Vibrational Doses Less than 17 minutes  of continuous vibration Less than 100,000 cycles of continuous vibration Less than 0.5 joule/cm3 of continuous energy dissipation into heat Less than 0.5 km distance traveled in a cyclic pattern

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Human subject reading task Three males and three female speakers “Goldilocks” bedtime story Monotone, normal, and highly expressive speech (exaggerated intonation and stress)

Average doses per second

Recovery times SHORT TERM restore circulation restore water to tissue remove lactic acid replenish calcium LONG TERM repair extracellular matrix repair blood vessels grow epithelial cells repair basement membrane

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Risk Factors in Vocalization Vibration over-dose Lack of recovery time Poor tissue environment Genetically weak tissue structure Poor vocal efficiency (economy)

Genetics Factors Thickness of mucosa Toughness of skin (epithelial cells), basement membrane, and extracellular matrix Proteoglycan (liquid) composition Vocal fold geometry (length, thickness, left-right symmetry, etc)

Poor Tissue Environment Dehydration Smoke, chemicals, pollens Drugs Inadequate Nutrition

Vocal Economy Factors Optimal adduction (between pressed and sigh) Use of inertive vocal tract  to lower phonation threshold pressure (resonant voice in speech, vocal ring in singing) Warm-up and cool down with low amplitude vibration (semi-occluded vocal tract) Best pitch for required loudness variation (from Voice Range Profile)

Chant Therapy: A pilot study with  Dan McCabe

Two auto-perception ratings (good for teachers) Amount of “effort” used in phonation Quality of “soft” voice

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Expected clinical protocol with teachers

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THE MOLECULAR  UNDERPINNINGS

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How do we engineer tissue that can withstand vibrational forces? Determine a typical amplitude of vibration Convert this amplitude to an equivalent vocal strain Design a bioreactor to impose this strain Allow cells to grow and express themselves in this shaky environment

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Shear deformation of the vocal fold

Calculation of vibrational strain displacement

Numerical estimate of shear strain Amplitude A =1.0 mm  Vibrational Thickness T = 3 mm Strain = 2A/T = 0.6  (60%)

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Vocal fold oscillatory amplitude vs. excess pressure over threshold (data from Titze, 1989)

Dynamic viscosity of the vocal folds (data after Chan & Titze, 1999)

Tissue Engineering Tasks Scaffold design Bioreactor design Rheological testing Gene expression analysis

For bioreactor design, how do we identify the appropriate vibrational forces? Determine a typical amplitude of vibration Convert this amplitude to an equivalent vocal strain Design a machine to impose this strain

Low frequency Forces

Vibrational Forces

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Candidate scaffold materials Synthetic polymer (elastomer) Collagen gel Hyaluronic acid gel Cellulose gel

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Important considerations Cell growth and protein expression Microscopic examination of engineered lattice structure Macroscopic assessment of mechanical properties Cell viability (at least several days)

What’s next? Understand the mechanism of recovery Build recovery times into vocal dose criteria Design auto-perceptive ratings of fatigue and recovery Test the exposure and recovery model on tissue in vitro and on human subjects

Promise for the future Engineered tissue will be used to replace scar tissue or otherwise damaged or weakened tissue (surgically) Engineered vocal fold tissue will be used in laboratory models to optimize vocal fold mechanical properties Teachers and other vocal professionals will be taught to self-monitor and improve their voice production, including the use of appropriate recovery  periods