Human vocal cord movements during voluntary hyperventilation.

Using a fiberoptic laryngoscope and video equipment, we studied the respiratory movements of the vocal cords during sustained hyperventilation in 4 normal human subjects. The expiratory narrowing of the glottic airway that occurs in quiet breathing was attenuated during hyperventilation in 7 of 8 experiments, and the pattern of vocal cord movements throughout the breathing cycle closely resembled the patterns previously found in exercise and hypercapnia. These responses were similar during normocapnic and hypocapnic hyperventilation. The similarity of laryngeal movements in voluntary and involuntary hyperpneic states suggests that common brain stem mechanisms may be entrained by both 'behavioral' and 'automatic' ventilatory control systems.