Tracheal Constriction in the Dog

Balloon and tambour recordings frequently revealed spontaneous, slow, rhythmic constrictions of tracheae in anesthetized dogs. Strong contractions were also induced in previously quiescent tracheae by asphyxia and, to a somewhat lesser degree, by rebreathing. Varying degrees of hypoventilation, achieved by regulation of the rate or stroke volume of a respiration pump (open-chest preparations) were, likewise, paralleled by corresponding degrees of tracheal constriction. Furthermore, a direct relation was demonstrated between the concentration of CO 2 in the inspired air and the degree of tracheal constriction. The induced contractions could be prevented or, once produced, abruptly relaxed by sudden overinflation of the lungs. The significance of these mechanisms is briefly discussed.