Gas exchange in the insect tracheal system.

The role of the insect tracheal system in gas exchange during cyclic ventilation is investigated using mathematical models. Three models are presented, one to describe the important elements of gas exchange during each of the three phases of cyclic ventilation. The effects of normobaric hypoxia on gas exchange are then examined, first assuming the initial parameter values set for the tracheal system and, second, assuming conditions of tracheal hypertrophy produced by an increase in the cross-sectional area of the tubes in the tracheal system. An increase in tracheal tube cross-sectional area is an important adaptation to normobaric hypoxia, but only if the tracheae themselves are the primary sites of resistance to gas exchange. Under conditions where the spiracles are the sites of resistance to gas exchange, volume expansion of the tracheae, not an increased cross-sectional area per se, is the important adaptation to normobaric hypoxia.