Narrowing of glottis opening in humans associated with experimentally induced bronchoconstriction

An index of the separation of the vocal cords during tidal breathing was obtained in humans; the area of the glottis opening was assessed from photographs of the vocal cord taken on inspiration and expiration via a fiber-optic bronchoscope. The index of glottis width was calculated from the area by dividing it with, as reference, the anteroposterior diameter of the glottis, a relatively invariant measurement of the glottis during breathing. Both inspiratory and expiratory glottis width decreased after histamine had been inhaled (dose range 2.4-9.6 mg) or injected intravenously (dose of 4 micrograms/kg), being associated with a reduction in forced expired volume in 1.0 s. Histamine, which acts directly on smooth muscle or bronchial irritant receptors, is unlikely to have directly caused contraction of the striated laryngeal musculature or to have stimulated receptors above the vocal cords. The narrowing of the glottis opening observed in humans may represent a reflex narrowing of the glottis in association with a reduction of intrapulmonary airway caliber.