Download Voice Quality Measurement: Aerodynamic Methodologies

The Larynx as an Energy Transducer
Voice Quality Measurement:
Aerodynamic Methodologies
•Aerodynamic energy
•Subglottal pressure (SGP) and airflow
•Acoustic energy
•Sound
•Vocal efficiency (VE) (Titze 1992)
Jack J. Jiang, M.D., Ph.D.
Matthew R. Hoffman
University of Wisconsin – Madison
Department of Surgery
Division of Otolaryngology – Head and Neck Surgery
Non-aerodynamic Measurements
•Electroglottography (EGG)
•Evaluates efficiency of larynx
•Ease of phonation
•Is patient producing appropriate level of
sound given the aerodynamic input?
Aerodynamic Parameters
•Airflow, Mean Flow Rate
•Insensitive to open phase of
glottal cycle
•Maximum phonation time
•Photoglottography (PGG)
•Subglottal pressure (SGP)
•Insensitive to closed phase of
glottal cycle
•Laryngeal resistance
•Videostroboscopy
•While able to diagnose several
vocal disorders, cannot provide
information on inputs of voice
production
•Acoustic power / aerodynamic power
•Phonation threshold pressure
Simultaneous
videostroboscopy (top) and
photoglottography (bottom).
Habermann 2000.
•Phonation threshold flow
•Measure parameters at instant phonation starts/ends
•Perceptual analysis
•Subjective, qualitative
Subglottal Pressure (SGP)
•Also abbreviated as Ps or Psub
•Generated by lungs, diaphragm, and intercostal
muscles
Mean Flow Rate (MFR)
•Average airflow passing through the glottis per
second (ml/s)
•Influenced by frequency and intensity
•Drives phonation
•Laryngeal disorders cause increase in MFR
•Important and difficult parameter to measure
•Hoarseness
•Influenced by frequency and intensity
•Normal range of 5-10 cmH2O
•Patients compensate for air leakage due to an
incomplete glottal closure by increasing MFR
1
Laryngeal Resistance
•Pressure = Airflow * Resistance
Invasive Measurement Techniques
•Tracheal puncture (Isshiki 1964)
•Laryngeal resistance = SGP / glottal airflow
•Insertion of pressure transducer through trachea
•Allows for direct measurement
•Measured in units of cmH2O/l/s or cmH2O/ml/s
•Average value = 20 cmH2O/l/s
•Painful, time consuming
•Body plethysmography (Tanaka 1983)
•Body (below neck) is placed in air tight box
•Influenced by many factors
•Thoracic pressure changes are calculated
•Age, gender, laryngeal disorders
•Calculate lung volume
•Complex machine, intricate calibration (Mead 1960)
Invasive Techniques (cont.)
Calculates volume and
pressure changes in the
chest cavity. Hixon 1972.
Noninvasive Measurement Techniques
•Intra-esophageal balloon (Lieberman 1968)
•Measure changes in pressure inside balloon inserted below glottis
•Showed strong correlation to pressure measured directly via
tracheal puncture
•Transnasal pressure transducer (Kitzing 1975)
•Probe with two pressure sensors passed through nose to glottis
•Intraoral (Rothenberg
1973, Hertegard 1995)
•Labial interruption
•Repetition of plosive
/p/
•Creates continuous,
enclosed system
Plots of SGP measured
using a tracheal puncture
(solid line) and an
esophageal balloon
(dotted line) during
speech. Lieberman 1968.
•Pressure is equal at
all points throughout
system
Repetitions of the syllable /b ae
p/. Lines indicate measured Ps
between neighboring labial
interruptions. Rothenberg 1973.
Y-axis = pressure
X-axis = time
Noninvasive Techniques (cont.)
•Mechanical Interruption
Noninvasive Techniques (cont.)
•Kobler, Hillman, Zeitsels,
and Kuo 1998
•Eliminates variability associated
with subject-controlled labial
interruption
•More consistent results
•Can elicit laryngeal reflexes
•Noise created by device can be
distracting to subject
•Novel system combined
endoscopic measurement of
glottal area with
aerodynamic measurement
of pressure and flow
Mechanical interruption.
Bard 1992.
Rising of intraoral pressure
during interruption. Bard
1992.
•Aerodynamic
measurements predicted
glottal area; measurement
confirmed by endoscopy
Relationship between measured areas and
areas predicted through pressure-flow
relationship. Kobler 1998.
Y-axis = predicted area, X-axis = actual.
2
KayPENTAX Aerophone
Currently Available
Aerodynamic Devices
•Labial interruption
•Computer-based data
collection
•Records 22 parameters
•SGP, airflow, acoustic
KayPENTAX 2007.
•Max, min, mean values
•Can be used in conjunction with
stroboscopic or acoustic systems
Rothenberg Mask
•Found volume velocity
waveform at the glottis by
inverse-filtering the volume
velocity waveform at the mouth
Glottal Enterprises MS-110
•Labial interruption
•Measures pressure and
airflow
•Can be combined with Glottal
Enterprises Aeroview or
Waveview software
•Inverse-filtering of oral
airflow
•Displays EGG, mean airflow
and sound pressure level
Pneumotachograph response to
constant airflow. Rothenberg 1973.
Y-axis = mask pressure
Circumferentially vented
pneumotachograph mask. Rothenberg
1973.
•Can be used for singing
voice analysis
MS-110 transducer electronics
system. Glottal Enterprises
2007.
X-axis = air flow
Difficulties in Measuring SGP
•Accuracy
•Must be confirmed through simultaneous direct measurement
•Precision
•High intrasubject variability
•Inability to sustain constant phonation
Current Aerodynamic
Research
•Laryngeal adductor reflex (LAR) response
•120-150 ms after stimulus (Kearney 2005)
•Varying frequency or amplitude between trials
3
Airflow Interruption for detecting PTP
(Jiang 1999)
•Pressure plateau
•Sufficient for equilibration
of supraglottal with
subglottal pressure
•Simultaneous direct
measurement on a
tracheotomy patient
•Subjects phonate constant /a/
•Can measure SGP, airflow,
acoustic output, and PTP
•500 ms mechanical
interruption
•Validation
Airflow Interruption (cont.)
Results of testing the device
in a patient with tracheotomy.
R2 =0.9550.
Y-axis = predicted SGP
X-axis = actual SGP
The airflow interruption system. Jiang 1999.
Incomplete Airflow Interruption (Jiang 2006)
•Measure SGP without stopping flow
A – valve closure. B – rising of supraglottal
pressure. C – phonation ceases. D supraglottal pressure equals the SGP. D
minus C equals the phonation threshold
pressure. Jiang 1999.
Airflow Redirection (Baggott, Jiang 2007)
•Several shorter interruptions (135 ms) to prevent onset of LAR
•Ohm’s Law
•Redirect airflow into a 5 liter tank
•V=IR
•Voltage = Current x Resistance
Two valve interrupter with pneumatic resistor.
Jiang 2006.
•Pressure trace is much more stable than when measured intra-orally or
within small device
•Modified Ohm’s Law as applied to
aerodynamic laryngology
•Subglottal pressure =
Glottal airflow x Resistance
•Incomplete airflow interruption
Exhaust
•Used known resistor and constant
airflow to calculate SGP
•Therefore, can always calculate third
parameter if you know other two
Circuit created by experiment. Impedance of
each output branch of the mouthpiece (Z1, Z2)
is known; airflow (U1, U2) is measured through
each output branch; glottal resistance (ZG) and
subglottal pressure (P) are unknown. Jiang
2006.
Airflow Redirection (cont.)
•20 subjects
•Mean SGP of 6.5 cmH2O
•13 subjects had standard deviations < .5 cmH2O
•Tracheotomy patient
•Simultaneous direct measurement for validation
•Device measured 16.83 cmH2O while tracheal puncture
measured 17.6 cmH2O (4.83% error)
The first plot is the
pressure within the air
tank during the trial with
a tracheotomy patient.
The following plot is
taken from the pressure
transducer directly
measuring SGP.
Y-axis = SGP
X-axis = time
Schematic of the redirection system. Baggott 2007.
Auditory Masking
•Hoffman and Jiang 2007, under
review
•Record stable sample of subject
phonation and play back over
headphones during trial
•Block ambient noise, provide target
pitch
A - Interruption begins. B – Equilibration.
C – Interruption ends. (A-C = 500 ms)
•n = 15; average intrasubject
standard deviation decreased from
1.286 to 0.568 cmH2O (p < .001)
•Facilitated subject maintenance of
a constant glottal configuration
•Necessary for noninvasive
measurement of SGP
Schematic diagram of experimental setup.
4
Reliable Time Constant (Hoffman, Jiang 2007)
•In press
•Simple tests provide information on voice input
•Measure SGP consistently at 150 ms
•Record measurements each clinical visit
•Sufficient time for supraglottal pressure to
equilibrate with subglottal pressure
•Evaluate treatment efficacy
•Eliminates effect of LAR
•Compare 150 ms measurement to
plateau analysis
Applying Aerodynamics to the Clinic
A.
B.
SGP measured at 150 ms time constant.
SGP measured using plateau analysis.
•n = 25; average intrasubject standard
deviation decreased from 1.112 to 0.664
cmH2O (p < .0005)
•Track patient progress / potential of pathology
•Acoustic abnormalities can be masked through voice
training, but patients cannot mask elevated input level
•Provide additional diagnostic parameter
•Validated using mechanical pseudolung
•Known pressure input
•Compare to value measured by device
Pseudolung validation data. R2 = 1.
Conclusions
•Complete picture of vocal health cannot be obtained
without considering the aerodynamic inputs of
subglottal pressure and airflow
Acknowledgements
Included studies and pilot data analysis were supported by
NIH grant number R01 DC008153 from the National
Institute on Deafness and Other Communication Disorders.
•Though many methods have been proposed to
measure SGP, there is still significant room for
improvement
•Accuracy, consistency, ease of measurement
•However, using current techniques will still provide
valuable information
5