Phonation and Laryngeal Mechanics - Study Notes (copy)

Phonation: Sound Source for Speech

• Phonation is the production of voiced sound by using air under pressure to generate phonation; acoustically it creates the sound source for speech that can be perceived and heard.
• Functions of the larynx include: voiced sounds = phonation; voiceless/non-phonation; vocal pitch; loudness; voice quality; as well as biological roles such as holding breath, swallowing, and coughing.
• Location: larynx sits on top of the trachea and sits between the upper and lower respiratory tracts; it controls passage between the tracts and protects the airway.
• In sum: the larynx produces acoustic events for speech and has important biological roles.

Laryngeal Framework and Supporting Structures

• Framework includes the cricotracheal membrane and the hyoid bone, providing support and muscle attachments.
• Hyoid bone:
  • Only bone in the body not attached to another bone.
  • Movement: forward and up, backward and downward movements assist in phonation control.
• The laryngeal framework encases laryngeal structures and provides muscle attachments and airway protection.

Vocal Folds (True Folds) and Related Structures

• True vocal folds (vocal folds) are the sound source; glottis is the variable space between the vocal folds.
• Vocal folds consist of vocal ligaments and thyroarytenoid muscle; located between each arytenoid and along the midline of the thyroid cartilage.
• Shape: triangular; in adults, length is just under a certain anatomical measure (text contains missing data here).
• Appearance: true folds appear white bands in a living larynx; real color closer to pink.
• False vocal folds (ventricular folds): located above true vocal folds; contain mucous glands that lubricate true vocal folds and do not produce phonation; ventricular dysphonia is a rough, hoarse sound due to disease.
• Aryepiglottic folds: located at the lateral border of the epiglottis; muscle embedded within folds pulls epiglottis down.
• Cuneiform cartilages are embedded within aryepiglottic folds and may be visible as small lumps or tubercles.
• Quadrangular membrane: spans from the lateral border of the epiglottis to the arytenoids; upper edge forms part of the aryepiglottic folds.
• Supraglottal cavity: space above the true vocal folds; also known as the vestibule.
• Laryngeal ventricle: small cavity between the false and true vocal folds; lined with mucous membranes to keep folds moist and lubricated.
• Subglottal cavity: space below the true folds, just above the trachea.
• Piriform sinus: a space on the outer side of the quadrangular membrane.

Joints and Movement: Abduction, Adduction, and Pitch Mechanisms

• Cricoarytenoid joint: allows complex rocking and sliding movements of the arytenoids relative to the cricoid; movements control vocal fold position for inhalation, voiceless sounds, and voiced sounds.
• Cricoarytenoid: abduction moves folds away from midline to permit inhalation and voiceless sounds.
• Adduction moves folds toward midline to produce voiced sounds and protect airway during swallowing.
• Cricothyroid joint: between cricoid and thyroid; enables complex rotation and sliding; responsible for high pitch when contracted (increased tension and length changes).
• Arytenoid movement changes vocal fold length and tension; essential for phonation and airway protection.
• In sum: Aryteno- and cricoarytenoid joints allow changes in vocal fold position and length, enabling phonation and airway protection.

Glottal Configuration and the Glottal Cycle

• Glottis is a variable space between the vocal folds; configurations change with laryngeal adduction/abduction.
• Breathing states and glottal configurations:
  • Quiet breathing: minimal posterior cricoarytenoids activity before inhalation; results in a medium glottis.
  • Forced inhalation: large glottal muscle activity (posterior cricoarytenoids) to widen the glottis.
  • Voiceless sounds: glottis abducted (open), air flows through the glottis with no significant obstruction.
  • Voiced sounds: glottis adducted (partly to fully closed) to impede airflow briefly, creating voiced sound; posterior cricoarytenoid and other adductors involved.
  • Whisper: glottis narrow or small triangular opening at the back; air flow resistance is high but without vocal fold vibration.
  • Breath holding: adducted glottis, trapping inhaled air.
• Glottal cycle stages:
  • Stage 1: Prephonation
  • Stage 2: Phonation (closing phase): glottis narrow during exhalation; exhaled air pressure builds; when superior pressure rebounds, glottis begins to open from bottom to top.
  • Opening: glottis opens; exhaled airflow resumes; glottis closes again.
• In sum: the complete glottal cycle involves repeated adduction and abduction with medial compression by adductor muscles; this generates the sound source (phonation).
• Medial compression: the muscular force that brings vocal folds toward the midline; maintains a constant alveolar pressure to produce a steady glottal cycle and a continuous sound wave.
• Phonation is the result of repeated glottal cycles producing an acoustic event.

Phonation Threshold Pressure (PTP) and Hydrodynamics

• Phonation threshold pressure (PTP): the minimal alveolar pressure needed to initiate a glottal cycle; depends on desired loudness.
• Example given: minimum ~3 cm H2O corresponds to approximately ~15 dB SPL: PTP \,\approx\, 3\ \text{cm H}_2\text{O} \approx 15\,\text{dB SPL}.
• Observations: glottal cycle can be initiated with small alveolar pressure changes; louder speech requires higher pressure and different pressure dynamics.
• For louder speech, increased medial compression and higher alveolar pressure are required to maintain a stronger glottal closure and faster glottal cycles.

Vocal Pitch (Fundamental Frequency) and Its Life-Span Changes

• Vocal pitch is determined by glottal vibrations or the number of glottal cycles per second (fundamental frequency, F_o).
• Typical values:
  • Male: F_o \approx 125\,\text{Hz}
  • Female: F_o \approx 225\,\text{Hz}
• Changes across the life span (puberty onward):
  • In males, F_o drops dramatically due to longer and thicker vocal folds.
  • In females, F_o drops somewhat for similar reasons.
• Why changes: thicker vocal folds lower vibration frequency; thicker folds and changes in vocal tract length/shape influence resonance.
• After age 68, changes continue due to aging effects on vocal fold tissue and geometry.
• Summary: pitch changes with vocal fold length, thickness, and tissue properties across the life span.

Pitch Control and Laryngeal Tension/Compliance

• Goal: cycle pitch control by changing duration and rate of glottal cycles; changes in compliance alter voice quality and pitch.
• Mechanism overview:
  • Change vocal fold length and tension to alter glottal cycle length and tension via cricothyroid and thyroarytenoid muscles.
  • Tension increases pitch; compliance (stiffness) decreases pitch if cycles lengthen or shorten depending on muscle action.
• Two mechanical scenarios:
  • High pitch: longer, shorter opening/closing durations with greater tension; more compliant? Actually, higher pitch typically corresponds to longer, stiffer vocal folds and shorter opening/closing durations.
  • Low pitch: shorter, thicker, more relaxed folds with greater opening/closing durations; lower fundamental frequency.
• The higher the tension and shorter the opening/closing durations, the higher the pitch; the opposite results in lower pitch.
• Overall: pitch is controlled by laryngeal tension, muscle activity (thyroarytenoids, cricothyroids), and the resulting glottal cycle dynamics.

Loudness (Perceived Intensity) and Aerodynamic Forces

• Loudness is the perceptual correlate of vocal intensity/amplitude; linked to alveolar pressure and glottal closure dynamics.
• Conversational speech typically uses about 25\% of vital capacity above resting volume; loud speech uses more air volume and pressure.
• Whisper: no phonation; aperiodic turbulence; airflow becomes turbulent; no sustained phonation.
• Relationship to glottal dynamics:
  • Medial compression increases with loudness, increasing alveolar pressure and exhaled air velocity, leading to a stronger glottal closure and louder sound.
  • In loud speech, higher subglottal pressure and greater glottal closure create larger amplitude vocal fold vibrations.
• Potential voice health concerns: extended loud phonation can temporarily damage vocal capabilities due to sustained aerodynamic forces if not managed properly.
• Summary: loudness depends on inspiratory/expiratory dynamics, medial compression, and subglottal pressure; changes affect acoustic output and vocal health.

Acoustic Characteristics and Voice Quality

• Voice quality describes perceptual attributes of the voice beyond pitch and loudness, including:
  • Breathiness: easy air escape; high-volume air vibrations; e.g., morning voice.
  • Strain: tense vibratory patterns; roughness and breathiness.
  • Roughness: hoarseness, irregular vibratory patterns with possible high air flow.
• Common pathologies affecting voice quality:
  • Vocal nodules: callous-like growths from constant voice use.
  • Laryngitis: inflammation of laryngeal tissues.
  • Laryngeal cancer: related inflammatory changes.
• Endoscopy and aeromechanical observations:
  • Endoscopy provides perceptual level observation of the larynx from above by inserting a device through the oral or nasal cavity.
  • Oral route uses a rigid endoscope; high-speed imaging (2000–5000 frames/s) can be applied to record laryngeal activity; a rigid system may interfere with natural speech.
  • Aeromechanical measures provide information about laryngeal air flow and laryngeal airway resistance; important for assessing laryngeal integrity.
  • Laryngeal airway resistance is determined by the aeromechanical state of the larynx and airway.
• Acoustic observation integrates with endoscopic and aeromechanical data to visualize laryngeal function and measure related parameters.

Pharyngeal Cavity and Velopharyngeal Mechanism

• Key structures: velum (soft palate), velopharyngeal mechanism, and the pharyngeal cavity.
• Velum (soft palate): attached to the palatine bone, palatine aponeurosis, and tendinous sheet around the velum; acts with the pharyngeal walls to regulate opening between the oral and nasal cavities.
• Velopharyngeal mechanism: essential for shaping sounds by closing the passage between the velum and the posterior pharyngeal wall; controls nasal resonance and oral-nasal coupling during speech.
• Velum movement and velopharyngeal closure influence nasalization and resonance of vowels/consonants, critical for sound quality and intelligibility.
• Related spaces:
  • The velopharyngeal port is the opening that must be closed during most non-nasal sounds.
  • The velopharyngeal mechanism affects ongoing resonance and sound radiation through the oral cavity.
• The velopharyngeal mechanism plays an essential role in shaping sound and maintaining intelligibility, particularly for non-nasal phonemes.

Subglottal and Supraglottal Spaces: Summary of Spatial Anatomy

• Subglottal cavity: space below the true vocal folds, just above the trachea.
• Supraglottal cavity (vestibule): space above the true vocal folds; includes the vestibule and aryepiglottic structures.
• Piriform sinus: outer side spaces adjacent to the laryngeal inlet near the quadrangular membrane; relevant in swallowing and certain resonance effects.
• These spaces contribute to articulation, resonance, and phonation dynamics via aerodynamic coupling and acoustic filtering.

Connections to Foundational Principles and Real-World Relevance

• Laryngeal biomechanics connect anatomy (joints, membranes, and muscles) with function (phonation, airway protection, and swallowing).
• The glottal cycle demonstrates the coupling between respiration (air pressure), muscle control (adductors/abductors), and acoustics (sound production).
• Understanding PTP and vocal fold tension helps explain why loudness changes require more subglottal pressure and how fatigue or pathology can alter phonation thresholds.
• Pitch control via cricothyroid and thyroarytenoid muscles illustrates how small changes in tension and geometry affect fundamental frequency and voice quality.
• The interplay between velopharyngeal function and nasal resonance shapes speech acoustics, crucial for intelligibility and pronunciation in languages with nasal sounds.
• Endoscopy and aeromechanical measures provide complementary perspectives: perceptual (quality) vs. physiological (airflow and resistance) assessments—important in clinical voice evaluation and therapy.

Summary of Key Formulas and Quantitative Details

• Phonation Threshold Pressure relation (example):
  • PTP \approx 3\ \text{cm H}_2\text{O} \approx 15\ \text{dB SPL}.
• Fundamental frequency estimates:
  • Fo \approx 125\ \text{Hz} \text{ (Male)}, \quad Fo \approx 225\ \text{Hz} \text{ (Female)}.
• Loudness and airflow relationships are governed by alveolar pressure and medial compression, with higher pressure and greater compression producing louder phonation.
• High-speed imaging referenced: up to about 2000-5000\ \text{frames/s} for detailed observation of rapid laryngeal events.
• Vital capacity references:
  • Whisper: ~10-15% above resting vital capacity.
  • Conversational speech: ~25% above resting vital capacity.
  • Loud speech: greater air volume and pressure, with increased aerodynamic forces.

Practical and Ethical Implications

• Vocal health considerations emphasize the importance of proper phonation technique to avoid overuse injuries (nodules) and laryngeal inflammation.
• Clinical assessments (endoscopy and aeromechanical measures) aid in diagnosing voice disorders and guiding therapy while balancing safe observation with natural phonation tasks.
• Understanding velopharyngeal function is essential for diagnosing and treating resonance disorders (nasality) in speech.