OBSERVATION AND MODELING OF GLOTTAL BIPHONATION

Digital high-speed camera technique combined with laryngoscopy was use d to observe vocal fold vibration in a normal subject and a patient wi th paralysis of the recurrent nerve who were able to phonate simultane ously at two different pitches. This phenomenon is called biphonation. Previous clinical examinations of biphonation and diplophonia will be compared with our observations. Moreover, we employed a modified two- mass model of the vocal folds in order to fit simulated time series to the high-speed glottograms (HGG) extracted by image processing from t he digital picture sequences. By variation of the model parameters we generated waveforms which showed the characteristic features of biphon ation. We state that the appearance of to independent pitches bases on biperiodic or toroidal oscillations of the vocal folds. The main cond ition for biphonation is a laryngeal asymmetry causing a desynchroniza tion of the vocal fold oscillations which is reinforced by high pitche d phonation, incomplete closure and large subglottal pressure. We stre ss the importance of a combined application of high-speed camera techn ique and model simulations to explain the mechanisms of hoarseness. It is a very successful method to isolate physiological parameters which categorize and quantify vocal disorders.