The Significance of This Research
According to the National Institute of Deafness and Other Communications Disorders (NIDCD), voice dysfunction affects approximately 7.5 million people in the U.S. every year.2 Educators have a high incidence of voice dysfunction, and others who are commonly affected include doctors, nurses, attorneys, performers, and salespeople. Typically these problems result from vocal fold (VF) paralysis of one (most common) or both (a more rare condition) of the vocal folds due to overuse of the voice.
Additional causes for voice dysfunction include physical trauma to the larynx, viral infections, neurological diseases, cancers, inflammation and nodules or growths on the vocal folds. Symptoms of vocal fold paralysis can be distressful and disruptive to daily life, and may include hoarseness, difficulty breathing, choking when eating, coughing, and shortness of breath, among others.
Challenges in Studying Human Phonation and Voice
Human phonation and voice are unique to each individual. Voice is how we inform, persuade, inspire, express ourselves, and connect with others. When there is damage to the mechanics of the human voice, disruption in other areas of life can ensue, including the ability to continue working and flourish in social situations.
Upon breathing, the vocal folds open, and upon swallowing, they close. The ability to speak results from the interaction of aerodynamic forces, fluid dynamics and structure of the vocal folds, which vibrate as they allow air to pass through, resulting in speech.
The study of human phonation and voice is challenging, as the larynx and vocal folds are difficult to visualize and access. Studies of excised canine larynxes provide useful information but have their limitations. Physical models created of various substances can mimic the complex tissue layers, and aerodynamics and physical structure of the larynx and surrounding structures. However, it is difficult to translate data from these models to actual conditions of human physiology. Computational modeling has the potential to model phonation problems with all their complexities.3
Current Treatment of Vocal Disorders
Many vocal problems resolve within a year, with intervention by otolaryngologists (physicians and surgeons specializing in conditions of the head and neck) and speech-language pathologists, who can help patients with exercises and improved breathing techniques to make the voice stronger. If symptoms do not improve within a year, surgery may be the next option.
One surgical procedure involves insertion of an implant into the patient’s paralyzed vocal fold in order to hold the vocal fold in proper position. “This is a very uncomfortable procedure for the patient,” Zheng said. “It is performed in the operating room using only local anesthesia, as the surgeon wants to ensure the implant is in the proper position and the patient can speak.”
The NIDCD reports that it is common for these implants to require repositioning in an additional surgery in up to 25 percent of cases.4 This results in more discomfort for the patient as well as increased healthcare costs.
Steps to Discovery with Tecplot 360
The research of Zheng and his colleagues has the potential to alleviate the drawbacks of today’s treatment of vocal disorders. Tecplot 360 is the only visualization tool that he and his colleagues use to perform patient-specific modeling of human phonation and speech. Their ultimate goal is that one day, three-dimensional, computational flow dynamics modeling will enable scientists and surgeons to predict the proper size and configuration of vocal implants, making anesthetized surgery possible for patients, with fewer repeat surgeries required. Zheng highlighted that there are three phases to visualizing the model and the result.
- Phase 1: Researchers reconstruct a patient-specific model from the patient’s CT (computerized tomography) scan and then put the model into Tecplot 360 to check mesh quality.
- Phase 2: Researchers conduct numerical simulations to replicate the process of voice production. They then visualize the results using Tecplot 360, analyze intermediate results, and further debug the cases.
- Phase 3: Researchers analyze all results from the simulation and again use Tecplot 360 to create illustrations and animations for use in published journals and presentations.
The Power of Tecplot 360
Tecplot enables us to view the 3D vortex structure, the glottal jet flow and the movement of the glottis. The animation shows the iso-surface of swirl strength of the glottal airflow, the corresponding vibration pattern of the glottis, and the time history of flow rate in a patient-specific, computational model of the human larynx. These observations greatly enhance our understanding of the fundamental mechanism of voice production.
Although research data is very promising to date, Zheng notes that several more steps in the research process are required before a clinical trial can be conducted.
1. Xudong Zheng, assistant professor in the Department of Mechanical Engineering at the University of Maine, is working with his colleagues, Dr. Qian Xue from the University of Maine, Dr. Rajat Mittal from the Johns Hopkins University, and Dr. Steven Bielamowicz (MD) from the George Washington University Hospital to more fully understand the impact of fluid dynamics and the complex physics of human phonation and speech. Zheng received his Ph.D. in May of 2009 in Fluid Mechanics, Thermal Science and Energy, from The George Washington University in Washington, D.C. where his dissertation focused on the biomechanical modeling of vocal fold vibration and glottal flow aerodynamics during phonation. Previous studies included obtaining an M.S. degree in Aerospace Engineering from The Academy of China Aerospace Science, Beijing, China, and a B. S. in thermal power engineering at the Beijing University of Aeronautics and Astronautics.[/pl_alertbox]
2. NIDCD website: www.nidcd.nih.gov/health/statistics/vsl/Pages/stats.aspx, accessed 09/25/2013
3. Rajat Mittal, Byron D. Erath, and Michael W. Plesniak. Fluid Dynamics of Human Phonation and Speech. The Annual Review of Fluid Mechanics. 2013. 45: 437–67. fluid.annualreviews.org
4. NIDCD website: www.nidcd.nih.gov/health/voice/pages/vocalparal.aspx, accessed 09/25/2013