Comparison of human vocal cord movements during isocapnic hypoxia and hypercapnia.

Respiratory vocal cord movements were analyzed in healthy human subjects during air breathing and in isocapnic hypoxia and hypercapnia. In the majority of experiments, expiratory glottic narrowing was substantially greater during hypoxia than during hypercapnia. Because ventilations were carefully matched under these two conditions, it is concluded that hypoxic stimulation of peripheral chemoreceptors favors expiratory glottic narrowing and leads to a relatively high laryngeal airflow resistance. In contrast, hypercapnia is accompanied by low expiratory laryngeal resistance. Similar rates of expiratory airflow with these two stimuli must be achieved by different balances of the factors that determine this flow.