Time course of laryngeal aperture response to expiratory resistance loading in humans

Expiratory laryngeal restriction in normal humans is augmented immediately following expiratory flow resistance loading applied to the mouth. The time course of this increased narrowing reflects the dynamics of the physiological stimuli that govern laryngeal control during expiration. Lung volume, expiratory airflow and upper airway pressure are possible factors influencing the larynx, and a comparison of their dynamics with those observed for laryngeal narrowing during control and loaded expirations ought to indicate the possible contribution of each source. We examined the dynamics of lung volume, airflow and laryngeal aperture subsequent to single breath applications of small flow resistance loads (2 and 5 cm H2O.L-1.sec) in 3 subjects using video image analysis techniques to define accurately the laryngeal aperture variation with time. The earliest deviation of the loaded expired volume time course from the control trajectory lagged the earliest occurrence of a significant increase in laryngeal narrowing with the larger load. Augmented laryngeal narrowing occurred simultaneously with deviation of the expired flow from the control trajectory. The responses to the smaller load were noisier, but were consistent with the hypothesis that information other than lung volume modulates the early laryngeal response to these loads, and receptors responding to the rate of change of lung volume (airflow) and/or upper airway pressure may be involved.