Abstract
The glottis of man, which widens on inspiration, is a choked point on the airway, its lumen even when maximally open being less than that of the trachea. The glottis, however, is not the only point of obstruction, the nose being usually of greater significance, especially in carnivorous species. The nose does not change in calibre during respiration. Experiments were carried out in animals and man, consisting of measurements of intra-tracheal, intra-thoracic, femoral arterial, and right atrial pressures, to determine the effects of normal nasal obstruction of constant presence, increase in nasal resistance, rhythmic obstruction at the glottis, combined nasal and glottic obstruction, and of elimination of nasal resistance and elimination of glottic resistance. As a result of these experiments the early opinion that the pump action on the circulation was due mainly to obstruction at the glottis has proved incorrect, and the main point of resistance is the nose, which offers constant resistance, variable in wide periods of time but not so rapidly as the phases of respiration. It appears that the glottis is the point of fine adjustment.