Upper Airway Aerodynamics

• Articulators


  Movable structures in the vocal tract that influence how speech sounds are produced
• Resistance


  Opposition to airflow through the vocal tract
• Impedance


  Opposition to the propagation of acoustic energy through the vocal tract
• VP-Nasal Airway Resistance


  • Resistance to airflow through the velopharyngeal port, outer nose, and nasal cavities
  • Affected by status of VP mechanism and nasal airway status
  • Changes with speed of air flow (turbulent is faster and has higher resistance)
• VP-Nasal Acoustic Impedance


  • Opposition to the propagation of acoustic energy through the velopharyngeal port and nasal cavities
  • VP port can be adjusted to influence the degree of coupling between oral and nasal cavities
• VP Closure Forces


  Forces required to close the velopharyngeal port
• VP Function During Speech


  How the velopharyngeal mechanism operates during speech
• Pharyngeal-Oral Flow


  Airflow through the pharyngeal and oral cavities
• Velopharyngeal Airflow

  • Aerodynamic effect of VP
  • Resistance
  • Opposition to airflow through VP port, nasal cavities, outer nose
  • Resistance affected by status of VP mechanism and by nasal airway status
  • Resistance also changes with the speed of air flow
• VP-Nasal Acoustic Impedance

  • Acoustic effect of VP
  • Impedance
  • The opposition to the propagation of acoustic energy
  • VP port can be adjusted to influence degree of coupling between oral and nasal cavities
  • How much sound energy goes through each cavity

  
• VP-Oral Tract Closed


  Sound energy passes nasally, oral cavity acts as acoustic side branch

  
• VP Closure Forces


  • Velum must contact posterior pharyngeal wall with sufficient tightness
  • Different tasks require different levels of compressive force
  • VP closure may be adversely affected by conditions that prevent velar closure muscles from generating sufficient force
• VP Incompetence


  Can result from physiological issues (size of palate or velum, cleft palate) or from usage patterns (very high oral pressures, brass instrument players, stress VPI)
• Palatal Clefting


  • Incorrect fusing of two halves of maxilla
• VP Function During Speech


  • Movement patterns
  • Height variation
  • Gravity
• Velum Movement Patterns


  • Elevate the velum
  • Move lateral pharyngeal wall inward
  • Both (A) and (B)
  • Both (A) and (B) and move the posterior pharyngeal wall forward
• Velum Height Variation in Speech

  • Velar elevation greater for high vowels than for low vowels

  
• Gravity and Velar Elevation

  The position of the body/head relative to gravity influences the resting position of the velum
• Pharyngeal-Oral Lumen Size & Configuration

  • Variation in the lumen of each cavity is a result of adjustments in position of structures lining the airway
• Finite Element Model of Vocal Tract


  • Can use finite element models to e.g., model how cavities change as a result of muscle activation
• Pharyngeal-Oral Airway Resistance


  • Opposition to airflow through tract
  • Greatly affected by changes in vocal tract cross sectional area
  • Length change has a secondary effect
  • Most sensitive to changes in oropharynx, oral cavity, oral vestibule

  
• Variation in IOP with Voicing and Manner

  • Intraoral air pressure (IOP)
  • IOP for Vowels: close to atmospheric
  • IOP for Consonants: greater than atmospheric

  
• Variation in IOP with Age


  • Tend to see higher IOP for children
  • Vocal tract size
  • Comfortable speaking level
• Variation in peak airflow with age and sex

  • Adults > Children
  • Male adults > female adults
  • Recoil forces increase with age and size of lungs
• Pharyngeal-Oral Acoustic Impedance


  • Opposition to movement of energy (sound waves) through vocal tract
  • Affected by changes in cross sectional area of tract

  
• Pharyngeal-Oral Biological Functions: Chewing and swallowing
• VP Port Closed: Nearly all sound energy travels through oral cavity
• VP Port Open: Sound energy travels through oral and nasal cavities
• Cavity with lower resistance will have greater sound energy travel throguh
• Cavities can exchange sound energy
• Low vowels require low compressive force
• Oral consonants such as sibilants or stops require high compressive force
• High vowels tend to have higher compressive force
• Consequences of Palatal clefting

  • Smaller palatal levator
  • Muscle malpositioning
  • Muscle abnormalities
  • Scarring
• People with cleft palates may not be able to exert as much closure force, and it may require significantly more muscle effort to do so, raising possibility of fatigue
• High vowels are more likely to be produced with a closed VP and greater closure force
• Velar elevation is related to tongue position and oral acoustic impedance
• Tethering is likely not responsible for velum height for high vs. low vowels
• Upright posture - gravity acts to lower the velum, needs muscle effort to overcome forces during closing, muscle forces to open velum will be augmented by gravitational pull
• Supine posture - Gravity acts to pull velum toward posterior pharyngeal wall, closure muscle forces augments pull, opening forces work against it