Effect of intermittent positive pressure application on the bulk modulus of the developing rabbit trachea

Tracheal dimension, pressure-volume relationships and bulk modulus (K) were determined in excised fetal and adult rabbit tracheal segments before and after application of intermittent positive pressure (IPP) which was 0--25 cm H2O pressure, at 30 cycles/min, and for a duration of 60 min. Both tracheal elastic behavior and dimensions underwent dramatic changes following IPP. At 21, 27, 31 days gestation age, the bulk modulus, K, of the rabbit trachea approximated those of the adult control values. However, the adult values of K did not vary significantly after IPP. The associated increase in tracheal dimensions were also related to the maturity of the animal. Significant structural and functional barotrauma is thus sustained by immature airways, and may account for the tracheal deformation frequently observed as a result of IPP.