Laryngeal resistance to respiratory airflow in humans.

Although vocal cord adduction has been observed during expiration, measurements of absolute values of resistance changes in man have not been reported in the literature. The authors measured resistance to translaryngeal respiratory airflow in inspiratory and expiratory phases of the respiratory cycle of four healthy, awake men during nasal breathing. It was found that, during quiet breathing through a decongested nose, translaryngeal resistance was 1.245 cm H2O/L per second in expiration and 0.354 cm H2O/L per second in inspiration (.005 < P < or = .01), for a percentage of approximately 25% and 50% of extrathoracic expiratory and inspiratory resistances, respectively. Voluntary hyperventilation decreased expiratory resistance, and a partial nasal obstruction abolished the statistical difference between translaryngeal inspiratory and expiratory resistance. These results are in agreement with previous observations of vocal cord movement and are consistent with an expiratory braking effect on airflow.