Physiological measures:

  1. Phonation threshold pressure: the minimum amount of sub-glottal pressure needed to set the vocal folds into vibration. 
    1. Conversational speech:  3cm H20 at low fundamental frequencies to 6cm H20 a high fundamental frequencies.
  2. Maximum phonation time: the longest period of time that an individual can sustain a vowel in one breath.  An adult speaker should be able to sustain comfortable phonation for about 15 to 25 seconds.   Children for a least 10 s. A lack of ability to sustain phonation for the expected amount of time indicates a problem in adequately valving the air stream for speech

Lung Volumes (single lung volumes)

  1. Tidal volume (TV): volume of air inhaled and exhaled during a cycle of respiration; Males: 600-750cc; Females 400cc
  2. Inspiratory reserve volume (IRV): Volume of air that can be inhaled above tidal volume (1500-2500cc)
  3. Expiratory reserve volume (ERV): Volume of air that can be exhaled below tidal volume (1000-2000cc)
  4. Residual volume(RV): Volume of air remaining in the lungs after a maximum expiration and that cannot be voluntarily expelled (1000-1500cc)

Lung Capacities (include two or more volumes)

  1. Vital capacity (VC):  Volume of air that can be exhaled after maximum inhalation (IRV + TV + ERV) Adults: 5000cc
  2. Functional residual capacity (FRC): Volume of air remaining in the lungs and airways at the end-expiratory level (ERV +RV) Adults: 2500-3500cc
  3. Total lung capacity (TLC): Total amount of air the lungs can hold

      (TV + IRV + ERV + RV) Males: 6000cc; Females 5000cc.

  1. If a person can generate a steady stream of air to displace 5cm H20 for 5 seconds, the respiratory system may be sufficient to support speech

Airflow: Normal airflow may range between 50 and 200ml/sec. 

Clinical implications:Steady airflow measures are greater for people with pathology.

Air pressure: The magnitude of air pressure beneath the vocal folds is important in producing vibration and determining the intensity of the sound. Typical pressures beneath the vocal forlsd (subglottal air pressure, lung pressure, or alveolar pressure) range from about 0.3 to 2.0 kPa (one kPa is approximately equal to 10 cm H20) depending on the loudness of the sound.  Pressures between 0.2 and 0.9 kPa would be expected for conversational speech levels.

Clinical implications: Excessive variability in pressures could be associated with poor motor control of the vocal folds or of the respiratory system.

Vibratory Behaviors:

Vibratory behaviors are important in determining the final acoustic output of the vocal folds. Information about the vibratory characteristics can be obtained from stroboscopic examinations, electroglottography, inverse filtering or the oral airflow waveform (flowglottogram), and photoglottography. 

Clinical implication: With pathology, the pattern of glottal opening becomes irregular and distorted as does the airflow pulse.