A study on production mechanism of pathological voice

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The contribution of the vocal folds vibration pattern to voice quality has been investigated mainly on normal subjects. Because tools we have been applying to monitor the vibration is stroboscope and the stroboscope can give the idea of the vibration pattern when the vibration is regular. However, in case of pathological voice, there are no guarantee that the vibration is regular. It is rather natural to assume that the vibration is irregular. In order to understand the production mechanism, it is essential to have a special tool with high temporal resolution. We have been developing the high speed digital imaging system which allows us to monitor the vocal fold vibration with up to 9000 frame per sec. By utilizing this system, we could visualize the pathological vibration pattern seen in the vocal folds with some lesions. We investigated the production mechanism of the diplophonia which we sometime experience in laryngeal palsy cases. In diplophonia case, the vocal fold on each side v … More ibrates with different frequency. As a result, complete glottal closure is observed periodically resulting in the fluctuation of the acoustic amplitude. Since the amplitude fluctuation is quasi-periodic, we percept two different pitch. One is the fundamental frequency and the other is the modulation frequency. Another puqqling pathology is spasmodic dysphonia which is supposed to be dystonia on the vocal folds. Acoustic impression of the voice uttered by patients with spasmodic dysphonia is expressed as strained, creaky, intermittent and so forth. Those pathological voice quality is heard periodically. We monitored the vibration pattern at the moment of the abnormal voice. The vibration cycle has a long closed period and short open phase with small excursion of the vocal fold. This vibration produces the low tone and very rough impression which is similar to the acoustic impression of the vocal fry. We suppose that the pathophysiology of spasmodic dysphonia is hyperadduction of the vocal folds resulting in the tight glottal closure which suggest the therapeutic idea to weaken adduction force of the folds by injection of botulinum toxin. Less