Comprehensive Study Notes on Semi-Occluded Vocal Tract Exercises (SOVTE)

Introduction to Expert Presenters

  • Dr. Marco Guzman:

    • Affiliation: University of Los Andes (Santiago, Chile) and faculty member at the Summer Vocology Institute (SVI) at the University of Utah.

    • Experience: 10 years of research post-PhD; five years teaching at the SVI regarding the science and application of semi-occluded vocal tract exercises (SOVTE).

    • Laboratory: Managing the voice research laboratory at Universidad de los Andes.

  • Carol Acevedo:

    • Credential: Voice pathologist and doctoral student in Medical Sciences with a Master’s in health sciences research.

    • Experience: Over 10 years working in clinics and hospitals treating voice disorders.

  • Global Context:

    • Dr. Guzman and Carol Acevedo are among the most published authors on SOVTE worldwide.

    • Major worldwide contributors mentioned include Dr. Ingo Titze (University of Utah) and Dr. Anna Maria Laukkanen (Tampere University, Finland).

Defining Semi-Occluded Vocal Tract Exercises (SOVTE)

  • General Definition: SOVTE are voice exercises used for both voice rehabilitation and voice training. They involve lengthening the vocal tract and/or occluding (narrowing) it.

  • Broad Utility: These are currently the most evidence-supported voice exercises in the world.

  • Clinical Caveat: While they are powerful tools, they are not a "treatment" in isolation; they must be taught and used properly to be effective.

  • Primary Goals:

    • Promoting body sensory exploration.

    • Developing vibratory sensations (face, larynx, pharyngeal areas).

    • Achieving the sensation of "easy voice production."

Classification and Categories of SOVTE

  • Categorization by Occlusion Type:

    • Constant Occlusions:

      1. Tube phonation (in air or water).

      2. Water Resistant Therapy (WRT).

      3. Nasal consonant humming.

      4. Kazoo and finger kazoo.

      5. Hand-over-mouth technique.

      6. Lip bass and white bass.

      7. Closed vowels (e.g., /u//u/).

      8. Cup phonation.

      9. Semi-occluded ventilation mask.

    • Oscillatory Occlusions:

      1. Lip trills.

      2. Tongue trills.

      3. Raspberry sound.

    • Transitory Semi-occlusions:

      1. Voiced fricatives like /v//v/ or /z//z/ (consonant tasks).

  • Double Source of Vibration Category:

    • Defines exercises where there are at least two sources of oscillation.

    • Primary source: Vocal fold oscillation.

    • Secondary source: Water bubbles (in WRT), lip/tongue vibrations, or mechanical valves.

    • Examples: WRT, lip trills, tongue trills, and Positive Expiratory Pressure (PEP) devices like the Acapella Choice or the Shaker.

Water Resistant Therapy (WRT) Specifics

  • Materials:

    • Finnish Resonant Glass Tubes: A traditional European option.

    • Flexible Silicone Tubes (LaxVox): A 35 cm length tube with a 1 cm diameter (alternatively, a garden hose can be used).

    • Drinking Straws: Less ideal due to small inner diameters, but functional in air or water.

  • Key Variable: The depth of submersion (usually 2-3 cm for resonance, though the lecture notes 10 cm for high adduction targets) is the main variable affecting physiology.

  • Proprioception: Patients should focus on the "massage-like" sensation in the larynx and the front of the face.

The Physics and Science of SOVTE

  • Nonlinear Source-Filter Interaction:

    • In a linear system, the source (vocal folds) sends input to the filter (vocal tract) to create output (voice).

    • In the nonlinear system utilized by SOVTE, there is feedback from the filter to the source. The shape and occlusion of the vocal tract physically facilitate or hinder the vibration of the vocal folds.

    • Secondary feedback occurs from the filter to the breathing function (e.g., closing lips tightly naturally increases abdominal muscle activation).

  • The Concept of Impedance (ZZ):

    • Impedance is the difficulty to move a system or the lack of response to a stimulus (subglottic pressure).

    • Resistance (RR): Occurs when stimulus and response are in phase.

    • Reactance (XX): Occurs when there is a time delay or advance in response.

      1. Negative/Compliant Reactance: Hinders vocal fold oscillation.

      2. Positive/Inertial Reactance (Inertance): Facilitates vocal fold oscillation.

  • The Inertance Formula:

    • Xi=ρ×LAX_i = \rho \times \frac{L}{A}

    • Where:

      • ρ\rho (rho) = density of air.

      • LL = length of the air column (tube length).

      • AA = cross-sectional area (inner diameter of the tube).

    • Implication: A longer and narrower tube produces greater inertial reactance (inertance), providing higher assistance to vocal fold oscillation.

  • Biomechanical Impacts of Inertance:

    1. Acoustic-Aerodynamic Interaction: Increases skewing of the glottal flow waveform, leading to increased energy in the high-frequency spectrum.

    2. Mechano-acoustic Interaction: Lowers the Phonation Threshold Pressure (PTP).

  • Phonation Threshold Pressure (PTP):

    • Definition: The minimum subglottic pressure (PsP_s) required to initiate or sustain vocal fold oscillation.

    • Significance: PTP is directly correlated with "self-perceived phonatory effort." Lowering PTP via SOVTE makes voicing feel easier.

The Aerodynamic Chain

  • Applying a semi-occlusion creates a chain of physical events:

    1. Increased airflow resistance.

    2. Increased oral pressure (also called "back pressure").

    3. Increased subglottic pressure (PsP_s) as a natural body compensation to maintain phonation.

    4. Increased intraglottal pressure: This pressure between the folds is hypothesized by Dr. Ingo Titze to decrease vocal fold "impact stress" (the force of the folds hitting each other).

Anatomy and Vocal Tract Configurations

  • Raóul Husson (1960) Shapes:

    • Megaphone Shape: Open vocal tract, low impedance.

    • Inverted Megaphone Shape: Occluded lips/long tract, high acoustic impedance. High impedance is generally targeted for voice improvement.

  • The Epilarynx Tube:

    • Narrowing the epilarynx tube (the 2-3 cm tube right above the vocal folds) increases inertance and creates a "metallic" or "twangy" voice quality.

    • This is often used by singers (classical and Contemporary Commercial Music/CCM).

    • Instruction to students: This cannot be taught via biomechanical verbal instructions. It must be learned via trial and error paying attention to acoustic output.

Clinical Rationale for SOVTE Selection

  • Goal-Based Application:

    • Hypofunctional/Hypoadducted (e.g., Paralysis or Paresis): The clinician wants to increase vocal fold adduction. High resistance SOVTE (e.g., WRT with 10 cm submersion) are used to increase the contact quotient.

    • Hyperfunctional/Hyperadducted (e.g., Nodules, Polyps, Cysts, Edema, Muscle Tension Dysphonia): The clinician wants to decrease impact stress and adduction. Lower resistance exercises (e.g., lip trills, straws in air, or WRT at only 2-3 cm) are preferred to promote easy oscillation without increasing inflammation.

Practical Application Workshop (Carol Acevedo)

  • Distinction between Exercise and Task:

    • Exercise: The SOVTE itself (e.g., straw phonation).

    • Phonatory Task: The sound produced (sustained pitch, glissando, melody, message di voce).

  • Vertical Vocal Tract Configuration:

    • Involves a low laryngeal position, high velum, and wide pharynx.

    • Usually perceived by users as providing "more massage" and "easier voice" during SOVTE.

  • Glissandos:

    • Used for stretching and contracting vocal folds.

    • Instruction: Switch from chest to head register smoothly; pushing is a sign of incorrect execution.

  • WRT Setup:

    • Use a transparent bottle to monitor depth.

    • Keep the bottle vertical.

    • Wide diameter tubes (approx. 1 cm or 0.5 inch) produce more massage-like sensations than narrow straws.

Questions & Discussion

  • Q: How do you narrow the epilarynx level on its own?

    • A (Dr. Guzman): You don't use biomechanical instructions. It is impossible to control that part of the throat consciously via verbal cues. Use trial and error and focus on the "metallic" or "twangy" resonance output.

  • Q: Why does a wider tube feel more difficult to produce bubbles than a narrower straw?

    • A (Dr. Guzman): A narrower tube has more airflow resistance, meaning you have to push harder. Users usually feel narrower tubes are "harder" to push through. If a user feels a wide tube is harder, it may be due to differences in submersion depth or personal breath coordination.

  • Q: Is there a time limit on these exercises for someone with a voice disorder? (Referencing the 3-second rule in swallowing therapy)

    • A (Dr. Guzman): No standardized second count exists. The rule is: perform the task only as long as it feels 100% "easy." As soon as any effort is felt, the patient must stop. Never push until the end of a breath just for the sake of duration.

  • Q: What is the impact of tube length versus diameter?

    • A (Dr. Guzman): Research by Dr. Andrade shows that relative changes in diameter affect oral back pressure significantly more than relative changes in tube length. Therefore, a clinician should prioritize variety in straw diameters over variety in lengths.