Researchers at the Department of Communication Sciences and Disorders at the University of Iowa are using a rotational shear rheometer from Malvern Instruments to study stresses on the human voice.
Coupled with a piezoelectric driver, this rheometer measures the viscoelastic properties of soft tissue to study how vibration affects laryngeal cells.
The team is also part of the National Center for Voice and Speech (NCVS), a consortium of voice researchers and professionals from institutions across the country.
Dr Sarah A Klemuk, assistant research scientist, said: 'For those who use their voice as a primary tool of trade, knowing how to protect the ability to talk clearly is critical.
'School teachers are the most likely to experience problems - they are two to 32 times more likely to have a voice problem in their lifetime than other professional voice users.
'Our research aims to help professional speakers save their voices,' she added.
We generate sound when our laryngeal muscles draw the vocal cords (now known as vocal folds) together and airflow from the lungs causes them to vibrate.
The exchange of energy between the air stream and the tissue sets the tissue into sustained vibration - a purely biomechanical oscillation of the soft, non-muscular layers of the vocal folds known as the lamina propria.
The ability of the vocal folds to vibrate is therefore directly connected to their viscoelastic properties.
Pathologies such as nodules, polyps, scarring or sulcus are the result of a change in vocal fold viscoelasticity.
Toughened tissues make voicing sound rough, while talking becomes difficult and more difficult for others to understand.
To soften damaged vocal folds or reduce scarring, surgeons use injectables in the lamina propria of the vocal fold.
For these materials to improve voice quality, they must have viscoelastic properties well-matched to the native tissues.
In her most recent paper, Dr Klemuk delivers results demonstrating that accurate measurements of the influence of vocal fold [cord] injectables on viscoelasticity are now possible at physiological frequencies.
She said: 'The rheology system we have set up allows us to gather data on how cells in the larynx respond to vibrations at particular frequencies over time; simulating everything from normal, conversational speech - around 125Hz in males and 200-220Hz in females - to situations of over-use.
'Our results can help steer laryngologists towards selecting the most appropriate injectable in those cases where damage has already been done.
'We also intend to increase our general understanding of how our vocal cords function, so we might develop prevention techniques.
'The rheology is collected using a thoroughly vetted Gemini rheometer, known to be accurate and reliable at low frequencies in the range 0.01-100Hz.
'A specialised piezoelectric drive unit coupled to the rheometer is then applied to multiple samples across frequencies in the range 1-2,000Hz, allowing confirmation of accuracy in the overlapping measurements in the 1-100Hz cross over.
'By characterising the viscoelastic properties of human vocal folds, engineers can optimise the material formulation to suit actual frequencies that humans use in speech,' she concluded.
