Chronical electrical stimulation for treatment of aged voice

Age-related changes of the laryngeal muscles (atrophy) lead to an incomplete closure of the vocal folds and subsequently to a hoarse and breathy voice. In a constantly ageing society preservation of the voice up to higher ages is mandatory as many professionals are depending on their voice (e.g. teachers, call centre agents etc.). However, current therapy concepts speech therapy or surgery of the vocal folds cannot treat the underlying muscular atrophy and provide only symptomatic treatment. In this project we seek to reverse the age-related muscular atrophy by chronical electrical stimulation of the main laryngeal nerves. Based on previous work by our groups we want to perform bilateral stimulation of the laryngeal muscles over a period of 11 weeks in aged sheep. This will be achieved by implantable state-of-the-art microelectronics. Outcome parameters reach from the cellular (muscle fibres) to the anatomical levels (micro CT-scan and 3D-reconstruction) and comprise most importantly functional examinations (vocal fold vibration). This goal can only be achieved by close cooperation of two highly specialized centres. While the working group of Assoc. Prof. Markus Gugatschka from the Medical University of Graz, Austria can manage all tasks of animal surgery, follow-up, assessment of molecular and anatomical features, the group of Prof. Michael Döllinger from the Medical University Erlangen, Germany is specialized on functional examinations. These comprehensive trials are mandatory before entering clinical trials.

Age-related voice changes (presbyphonia) include a hoarse and breathy voice and a significantly reduced vocal capacity. Vocal fold (VF) atrophy, the wasting or thinning of the VF muscles, is the most frequent finding in patients with presbyphonia, with noticeable space between the VF (glottal gap) and curling of VF inwards due to muscle thinning. Current treatment is speech therapy, and laryngeal surgery that modifies the cartilage that houses the VF. However, these therapies do not treat VF atrophy, the cause of presbyphonia. Functional electrical stimulation (FES) is a method that uses electrical current to cause a muscle to contract, either directly or by stimulating the nerve. In a previous study using a sheep model, we implanted an electrode using a minimally invasive surgical approach and showed that one- sided FES of the nerve innervating the VF muscle (thyroarytenoid muscle, TAM) resulted in a significant volume increase of the stimulated TAM, compared to the unstimulated side. In the current project, we used the same approach but stimulated both sides of the larynx to investigate the functional consequences of TAM stimulation. Functional properties of the larynx, as well as effects of the stimulation on the tissue were investigated and compared to unstimulated animals. We found that the stimulated larynges had improved vocal efficiency, which is the ability to sustain voice, compared to the unstimulated larynges. Moreover, the larynges of the stimulated sheep had a reduced glottal gap during voicing and an increase in tissue flexibility, compared to unstimulated larynges. The muscle tissue analysis showed that type II muscle fibers (muscle subunits) were larger in diameter in the stimulated TAM compared to unstimulated TAM and that the muscle fiber composition, important for the function of the muscle, was unchanged. This was also confirmed on the molecular level. These results suggest that FES improves the voicing process for aged larynges or presbyphonia and could therefore be a candidate for presbyphonia therapy.