The mechanism of phonation; its pathophysiological aspects

Abstract

The phonatory function of the larynx and its disturbance were discussed on the basis of the author's data of 1) electromyographical observation of the human larynx, 2) radiographical study of the larynx, 3) measurement of the mean subglottal air pressure as well as the vibratory subglottal pressure variation during phonation, and 4) analysis of vocal cord movements during phonation with high speed cinematography. Chief findings are as follows: 1) In cases of recurrent laryngeal nerve paralysis, each electrical activity of the laryngeal muscles appeared in 4 different patterns, i.e. i) silent, ii) fibrillation voltage, iii) complex NMU voltage, iv) normal NMU voltage in compliance with the duration of the paralysis. Even when the normal NMU voltage was observed, the phenomenon of the misdirected regeneration of the paralysed nerve fibers was found in many cases. 2) In cases of unilateral recurrent laryngeal nerve paralysis, the paralysed vocal cord was usually thinner and situated lower than the healthy one. The shape of the subglottic cavity during phonation was rather spheric in the healthy side while it was parabolic in the paralysed side. 3) The subglottal air pressure varied synchronously with the pitch of the voice. The air pressure ascended during the closed phase of the glottis and descended during the opened phase. The mean subglottal pressure was higher in the diseased larynx such as laryngeal carcinoma and recurrent laryngeal nerve paralysis than in the normal one. 4) The vibration of the vocal cords was accompanied by the wave-like movement of the mucous membrane. When the larynx was affected the wave like motion first diminished and disappeared: for example, in the blowing experiment with the excised larynx, when the mucosa was dry the wave like motion disappeared and then the vibration of the vocal cords ceased. The author has put forward the mucoviscoelastic-aerodynamic theory pertaining to vocal cord vibration.