Mapping the biomechanical properties of the sub-glottal region of the human vocal tract

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Phonation, or our ability to speak, arises from the process of delivering a controlled exhalation of air across the vocal folds (often know as vocal cords). This causes the vocal folds to vibrate, at a frequency that can be controlled by our vocal muscles. The resultant airflow is now modulated and passes into our 'vocal tract', which is in effect our mouth. We then form the modulated air flow into sounds by muscular control of our tongue, lip and other vocal tract features.The starting point for phonation therefore is the oscillation of our vocal folds. As we exhale, the moving passage of air creates a pressure drop; this in turn causes these soft tissues to rise up, until they meet. When full closure occurs the airflow ceases, and the air pressure returns to normal, causing the focal folds to fall back again. It is this cycle, repeated at audible frequencies that creates the initial modulated airflow, that we form into sounds. This process is known as the myoelastic cycle; which was first described by Ingo Titze.Whilst visualisation of the vocal tract is readily achievable superior to the vocal folds, there is very little published data on the impact of low pressure inferior to vocal folds. Recent research has presented strong evidence that vortices form in the sub-glottal region, which will inherently aid closure by reducing the air pressure below the vocal folds.Our recently published work, using data obtained with our partners at Wisconsin Medical Centers presented data that indicated that the elastic properties of the sub-glottal mucosa were non-linear - such that their deformation under low pressure would cause a funnel effect inferior to the vocal folds. This variable deformation could offer support for the vortex theory. The study was carried out using porcine larynges. UKE Hamburg have offered us the opportunity to repeat this study using excised human donor larynges. The purpose of this OTG is to establish and enable the co-supervision of a Dotoral study that will measure and map the elastic properties of the sub-glottal mucosa in human tissue. This data will be made available to other international teams who are actively examining the importance of the aerodynamics of the vocal tract, and how it impacts on our ability to phonate. We will develop mathematical models to explain the data that is measured, and determine if it does support our theory that deformation of the mucosa below the vocal folds results in a funnel shape that promotes the creation of vortices. If our theory is correct then it indicates the importance of this region in giving us the ability to speak.In order to maximise the cost effectiveness of the grant we will also carry out trials of our innovative laser speckle skin analysis device. This has been developed to investigate if laser speckle can be used to detect lesions in skin (e.g. melanoma). We will carry out a series of experiments with excised donor human larynges to determine if laser speckle could also be deployed by phonosurgeons to detect tissue damage in vocal folds that is not visible from the surface. Other international research institutions have expressed interest in applying the laser speckle technique in new areas of research if the UKE study is successful.