VOCAL CORD CLOSURE - CAUSE OF UPPER AIRWAY-OBSTRUCTION DURING CONTROLLED VENTILATION

Abstract

Studies of vocal cord function were undertaken in a quadriplegic patient requiring ventilatory assistance and in 2 normal subjects during controlled ventilation in a tank-type respirator. When the patient and the normal subjects relaxed and made no conscious effort to assist the respiratory, the vocal cords closed during inspiration, and a large pressure gradient (12-19 cm H2O) developed across the cords. When the subjects made a slight inspiratory effort (assist mode), the cords opened widely during inspiration. There were large increases in flow and tidal volume in the assist mode compared with passive ventilation. Measurements of transdiaphragmatic pressure and esophageal pressure showed that these variables did not increase with the slight assist. Increases in ventilation during the assist mode appeared to be due to alleviation of inspiratory obstruction at the level of the vocal cords. The same phenomenon was observed in the patient during phrenic nerve pacing. A pacemaker was designed to be triggered by the electromyographic impulse from an accessory muscle of respiration. In this manner, vocal cord opening could be coordinated with the mechanical assist given by the phrenic nerve pacer.