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

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.

This research will help to develop our understanding of the importance and properties of the sub-glottal region, that is traditionally hard to visualise. The impact on a patients ability to phonate should this region be damaged will be better understood, enabling more informed choices to be made about intervention. Provision of new knowledge of the role of the deformation of the mucosa inferior to the vocal folds during phonation. This will be relevant to clinicians, medical physicists and engineers researching innovation in medical devices.

The laser speckle study is at early stages. However our initial results on skin are promising, with published results indicating that the technique is capable of visualising hidden lesions. If successful this early study could lead to the development a new diagnostic techniques and a diagnostic tool for use of vocal fold tissue, and other mucosal tissues. Thus we could lead in to a new programme with both medical and commercial impacts. Should our research be successful then will be able to take forward the development of an innovative diagnostic tool (for which a patent is being sought). This will deliver a device that will aid the early, and more precise diagnosis, of vocal fold lesions, and thus directly aid patients. The evaluation of laser speckle as the basis of a new diagnostic tool to visualise hidden lesions. This will therefore be relevant to clinicians seeking innovative diagnostic techniques. We will also be better placed to secure a business partner to commercialise the device. There is an extensive and well serviced pharmaceuticals and medical devices cluster in the East Midlands that we can use to disseminate any emerging medical device.

Finally the development of an international partnership with UKE Hamburg and the potential to develop new international collaborations in the USA and Sweden has the potential to deliver more than one new international collaboration. It will also enable us to promote any new medical device that might arise outside of the UK.