oa Editorial [Hot Topic: The Origin of Human Voice Production within the Larynx: The Interaction between Air Flow - Tissue Dynamics - Resulting Acoustical Signal (Guest Editor: Michael Dollinger)]

Voice research is a scientific area, which becomes more and more interesting not only for medical interested scientists or medical doctors but also for other scientific areas like mathematicians or engineers. Most of the communication disorders are due to a disturbance in voice due to laryngeal diseases. Voice is generated in the larynx by the two oscillating vocal folds. The oscillation range of the vocal folds is between 100 Hz and 300 Hz. They are the sound source and constitute the carrier signal for information being transferred through speech. A healthy voice (the acoustical signal) is generated by symmetric and periodic vocal fold oscillations. It is widely held that vocal fold vibration irregularities lead to an impairment of the acoustical voice signal (i.e. hoarseness). Although, this description sounds like an ordinary and easy to understand procedure, the understanding of basic principles of voice production is rather difficult and needs for highly interdisciplinary research approaches. Aims and scope of the given review article series are as follows. Clinical assessment of laryngeal diseases is performed by direct (i.e. endoscopic laryngeal imaging) or indirect (i.e. acoustic and aerodynamic) assessment techniques. However, detailed quantitative knowledge about interrelations between acoustic signal, dynamics of the voice generator, and applied airflow is still in its infancies. Here, the difficulties are due to the limited space within the larynx. Hence other analysis approaches have been developed yielding entire new insight in the process of voice production. The content of this mini hot topic review will first give an overview on up to date clinical assessment techniques, their abilities as well as their limitations (Ziethe et al.). This review yields the conclusion, that most of the assessment techniques only describe the disease but do not give information on laryngeal interrelations. Revealing interrelations in in vivo human experiments is rather impossible due to the very limited space within the larynx. Consequently, efforts on analysing interrelations based on in vitro human and in vivo/in vitro animal experiments are performed due to their vicinity to human in vivo behaviour (Dollinger et al.). In these experiments, relations between stimulation (e.g. muscle tension, air supply) and effect (e.g. dynamics, signal quality) can be analysed in detail. However, due to the reduced reproducibility of in vitro/in vivo experiments, synthetic models based on experience in in vitro experiments are successfully applied and analysed (Kniesburges et al.). Complementary and to verify findings, sophisticated numerical models like 2D-FEM or 3D-FVM models were developed (Alipour et al.). To bring artificial synthetic and numerical models closer to reality in vitro experiments applying rheometers or bio-ractors have been lately engineered to increase the knowledge on tissue attributes of epithelium and muscle, or to gain more insight into local differences on the vocal fold surface (Goodyer et al.). Most of the voice research is focused on “normal” voice production but not on processes occurring during singing voice. The last review article (Kob et al.) will show that this topic yields entire new challenges and that we are just at the beginning of understanding how singing voice is generated. All the proposed methods have the goal to increase our understanding on voice physiology and production within the larynx. In future, improvements for clinical treatment like conservative therapy, surgery or voice rehabilitation are expected.